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VDA-Recommendation 4955/2 1 Edition September 1999

VDAVDMA

"CAD/CAM" Working Groupin the VDA-Raw Material Committee (VDA-AK "CAD/CAM")

Scope and Quality of CAD/CAM data

4955

This recommendation serves the purpose of defining fundamental, common requirementson the quality, the scope and the control of CAD data.

This recommendation supplements the VDA recommendation 4950 "Exchange ofCAD/CAM data".

It represents the project results of the VDA working group "Scope and quality of CAD/CAMdata", as well as of the VDMA working group “ Communication and quality of design data“.

Edition 1 October 1993Edition 2 September 1999• Field of application has been expanded to include (VDMA, ODETTE)• Surface criteria revised and newly added, Solid's criteria added• General, system and user specific tolerance information added• System neutral specifications for check programs integrated (Chapter. 3)• Forms revised, examples for the use of forms removed

VDA-AK "CAD/CAM"Audi, Becker Group, Behr, BMW, Bosch, Brose, Continental-Teves, DaimlerChrysler, Delphi, Flachglas, Ford,Freudenberg, GETRAG, Happich, Hella, Iveco, Johnson Controls, Karmann, Keiper, Knecht, Kostal, Krupp-

Hoesch Automotive, Küster Automobiltechnik, MAN, Mannesmann Sachs, Mannesmann VDO, Opel, Pierburg,Porsche, Sekurit, Siemens, VW, Wabco, Webasto, ZF

VDMA-AK "Communication and quality of design data“Allgaier, Audi, AWB, Paul Beier, Benteler, BMW, Claas, Fagro, Krupp Drauz, Werkzeugbau Laichingen,

Läpple, MAN, Meleghy, Müller Weingarten, Thyssen-Nothelfer, Rath, Schuler

Publisher:Verband derAutomobilindustrie e.V. (VDA)Westendstraße 61Postfach 17056360079 Frankfurt/M. GermanyTelefon: +49 (0)69/97507-0Telefax: +49 (0)69/97507-261

Verband deutscher Maschinen- undAnlagenbau e.V. (VDMA)FG PWZ (DPV) im VDMALyoner Str. 1860528 Frankfurt/M. GermanyTelefon: +49 (0)69/6603-1251Telefax:

Copyright:Reproduction for distribution

(only the complete document)expressly allowed!

Comments to: [email protected]

VDA-Recommendation 4955/2 -2- Edition September 1999

Summary of the VDA aids for exchange of CAD/CAM data:

VDA-Recommendation4955

Scope and qualityof CAD/CAM data

Check program

VDA-Recommendation 4950Agreements concerning the exchange

of CAD/CAM data

(Liability of CAD data)

VDA-Recommendation 4951Remote data transmission of

CAD/CAM data

ENGPARTENGDAT

Neutral interface definitions

STEPVDAISVDAFS

VDA-Recommendation4952

Raster data exchange

VDA-Recommendation 4961Arrangements within the bounds of

Simultaneous Engineering(SE check list)


Contents

0 Introduction 4

1 Application of the recommendation 6

2 Data quality ......................................................................................8

2.1 General ..............................................................................................8

2.2 Data categories ...............................................................................13

2.3 Geometric data quality ....................................................................142.3.1 Wire geometry ...................................................................................142.3.2 Surface...............................................................................................192.3.3 Bounded surfaces, Face ...................................................................262.3.4 Composite surface / Surface groups, topology .................................292.3.5 B-Rep Solids .....................................................................................312.3.6 Drawing elements .............................................................................33

2.4 Organisation data quality ...............................................................342.4.1 Administrative information / Model name...........................................342.4.2 Model structuring................................................................................342.4.3 Drawings ............................................................................................352.4.4 Solids .................................................................................................36

2.5 Supplementary agreements............................................................402.5.1 CAD system parameter / tolerances .................................................402.5.2 Data quantities ...................................................................................432.5.3 Version CAD system..........................................................................432.5.4 Technological detail............................................................................43

2.6 Data scope .......................................................................................432.6.1 Scope of 3-D CAD data models.........................................................432.6.2 Exemplary production specific additions............................................442.6.3 Scope of CAD drawings ....................................................................46

3 Data check .......................................................................................473.1 General ..............................................................................................473.2 Fundamental conditions..................................................................483.3 Mathematical geometry checks (Summary) ..................................493.4 Organisational model checks.........................................................663.5 Structuring of the protocol data record ........................................67

4 User aids ...........................................................................................704.1 Further Information sources...........................................................704.2 Limit recommendations for check programs Version 1..............714.3 Limit recommendations for check programs Version 2..............72

Attachment1 Definitions of terms2 Comparison of the element types in

STEP/IGES/VDAFS and various CAD systems3 Form: Agreements concerning data quality


0 Introduction

Preface

Rationalisation as well as quality assurance efforts in the automobile and supplyindustry have led to the fact that, through the utilisation of CAD/CAM systems,drawings and physical models are no longer sufficient as a medium for productdepictive/descriptive data. Instead, the 3-D CAD data models, i.e. Faces, Volumemodels have consequently evolved as the principal information carrier in the mod-ern process chains for vehicle development.

The exchange of CAD models require a joint understanding not only of the CADmodel structure but also with regards to the required data quality.

The purpose of this document is to make possible an agreement which takes intoconsideration the quality requirements imposed upon a CAD model. Such anagreement should be concluded for every exchange of data within the automobileindustry. It should be published under the keyword “VDA CAD/CAM data qualityagreement”

This recommendation should be adopted by your company and customised toyour own particular requirements. It should also be adopted by the CAD/CAMsystem manufacturer as well, where it could intermediately contribute to an im-provement in the system.

The main users of this document would be the responsible personnel for CAD dataquality at each company, developers of quality assurance programs, as well as thevarious end users of CAD systems and data.

When reaching such an agreement, it is important that all users of the variousCAD data models are involved. This would comprise amongst others, personnelfrom styling, production, quality control and purchasing. This will ensure that theagreement is accepted and understood.

Over and above this, the partners have to come to an agreement concerning theform of the data communication. This agreement takes place normally before theconclusion of a “Quality of data agreement”. This higher ranking “Data exchangeagreement” will not be commented upon here. The competent document for thispurpose is the VDA recommendation 4950 “Agreement for the exchange ofCAD/CAM data”.

The VDA recommends that the sender of the data should be made responsible forcompliance with the data quality agreement. The VDA recommends further that,besides other information, all business agreements should contain references toboth these agreements. These should include penalties to be imposed by viola-tions, since these could possibly lead to enormous expense through loss of time,additional effort and inferior qua lity.

An important result of such data quality agreements is the universal understandingfor maintaining the data quality demanded or respectively, the consequences re-sulting by non-compliance.

Introduction


Several statements/suggestions to data quality:

• CAD models are utilised internally (within the company) as well as also exter-nally (after an exchange of data). The VDA recommends studies and agree-ments in both areas, as well as for harmonising both.

• “Sufficient” or “good” data quality is dependent upon the utilisation purpose. Itcan be sufficient for the one purpose (e.g. for concept release), however, foranother purpose, it can be completely insufficient (e.g. for production release).

• The model structure as well as the performance/marking of change conditionsare of special significance. Both shall be easily recognisable and understand-able.

Contact persons

The VDA homepage will (shortly) be available for questions and suggestions, inInternet: http://www.vda.de . As long as this is not the case, please direct yourcommentaries and suggestions to: [email protected]. Further contacts andsources of Information may be found in chapter 4.1.

Associated documents

Documents which are related to the source of supply (VDA Recommendation, etc.)may be acquired from the information sources according to chapter 4.1.

Terms

We have endeavoured to utilise “system neutral” terms (e.g. bounded surface,unified surface groups, etc.) even when occasionally, system specific terms areusual (e.g. Face, Volume, etc.). A glossary as well as a summary of the mostly re-quired geometrical terms may be found in the attachment.

Introduction


1 Use of the recommendation

The VDA recommends all companies to conclude Data exchange agreements in ac-cordance with the VDA recommendation 4950 and Data quality agreements corre-sponding to this document (VDA 4955), together with individual company specificrules and standards.These agreements may have different fields of application. An agreement might ap-ply to only one particular part, whereas another might be applicable to a group ofparts within a project. A fundamental agreement at company level could represent agood beginning and can form the basis for subsequent agreements.

Those involved (sender and recipient) should agree upon the following conditions:

• The category of the data quality using the “Data quality form”. This agreementshould be a part of the fundamental development and supply contract,

• That the sender is responsible for the content and for the quality of the CAD data,

• That the recipient shall check the received data in particular with respect to com-pliance with mutual agreements,

• That the sender shall be informed if deviations occur and that he is subsequentlyresponsible for forwarding corrected data.

Chapter 1: Application of therecommendation

Principle of the exchange of CAD/CAM data:

Firm / Department B (Recipient)

Firm / Department A (Sender)

CADQuality

assurance

CADDB

Data exchangeagreement

incl.CAD quality

CADQuality

verification

CADDB

Feedbackas “confirmationof contents” or

“order forimprovements

CAD model and docu-mentation of the quality


Procedural instructions:

For the conclusion of a data quality agreement we recommend the utilisation of theform for data quality (see attachment 3) as follows:

1. Start by stipulating the project partner (sender and recipient) who will be respon-sible for the quality of the CAD data, as well as the area of validity covered by theagreement (project/component part). Together with the datum, this informationshall represent explicit “fundamental specifications” for multi-sided agreements.

2. Stipulate then the intended use of the CAD data which is to be supplied. Often,several intended uses must be stipulated, where possible, listed in chronologicalorder. Only then is it meaningful to stipulate the associated quality criteria on oneform, however, it can also be more understandable to employ one form per in-tended use. At this point, one can use the categories (criteria and characteristics)according to chapter 2.2. Where possible, also give deadlines or time intervals forthe delivery of models in the required quality.

3. Classify then each intended use of a model/geometry type, where required, thedrawing type as well as additional stipulations (e.g. for the degree of detailing).

4. Then mark in the left hand column the affiliated quality criteria for the respectiveintended use which the sender and recipient have jointly assessed to be required.Please do not mark wholesale all criteria as being required, but concentrate onthe really important “minimum” requirements. A detailed description of the criteriamay be found in chapter 2.

5. Adopt then the limiting values for the “promoted” criteria as recommended orjointly stipulate other values. Utilise the lines if need be, also for a short justifica-tion, this will be useful during the utilisation by “third parties”.

6. With the exchange of CAD models the exchange of models with the status “workin progress” is necessary and common. Observance of the agreed criteria is to bestrived for, even for this model; however, this can perhaps (temporarily) not bepossible. For this reason, as a preliminary stage to “observing obligations”, the“documentation obligation” for data quality, which is permanently in existence, willbe defined. For this, the appropriate criteria shall be marked with a cross in theright column titled “fulfilled”, as indicating “observance of minimum documenta-tion”, and then turned over by the sender to the recipient (within the bounds of theusual confirmation of exchange of data) parallel to the CAD model. As an alterna-tive to this, there is also the possibility of employing the check program for thedocumentation (corresponding to chapter 3).

At the present time, it is not foreseen that this form will be used for a feedback, inform from a confirmation or error message, from the recipient.

It is requested, not only for reasons of quality assurance mechanisms accord-ing to ISO 9001, that in the case of company overlapping data exchanges it isimperative to use the VDA-Recommendation 4950 “Data exchange agreement”.

Chapter 1: Application of therecommendation


2 Data quality

This chapter describes the quality criteria for users of CAD systems. The user shallthereby be placed in a position which enables that person to develope a suitable(CAD quality orientated) design method, to conclude a “Data quality agreement” andto sensibly employ check programs.

2.1 General

The quality criteria is described in the following manner:A Problem description describes the criteria and the possible problems with an ex-change or during subsequent work upon the CAD data. An Illustration shall pictori-alize this description. The Solution proposal offers the user a recommendation forthe (interactive) resolution of the problem.

Concrete limits for the relevant criterion shall be arranged between the partners.Fundamental principles for this are contained in Chapter 4: User aids and companyspecific standards.

2.1.1 Branches of the data quality

Healing Methods

Data exchange User knowledge/Training

Check program CAD system routines

One of the principal influencing variables by the generation of data quality is the ap-plied method of CAD design. A design method that is attuned to the product, mate-rial manufacturing process as well as to the utilised CAD system is the basis forqualitative high-quality CAD data, which can be used in subsequent processes with-out having to rework the data.

Poor quality data causes numerous different reactions and problems in the varioussubsequent processes, e.g. by radiusing, by the generation of N/C machine pro-grams, by the exchange of data, by the generation of (STL-) models or FEM grids.

The impartment of knowledge regarding these consequences, the meaningful designmethods, as well as about the possibilities and limitations of the utilised CAD systemsare the principle building blocks of a successful training for the CAD user.Current, process orientated user knowledge is for this reason just as essential forthe generation of qualitative high grade CAD data.

Chapter 2: Data quality


The phenomenon of poor data quality is, for the most part, independent from the util-ised CAD system. However, a large potential for generation of such can also unfortu-nately be found in the CAD system routines. System internal procedures and algo-rithms, e.g. for sectional view operations, projections or for the generation of offsetscan lead to incorrect geometry that remains unnoticed or is even ignored by the user.

The three previously mentioned influencing variables with respect to data qualitymake Check programs necessary and logical, in order to permanently and criticallyinform the user about the quality generated by him. There are already a whole row ofappropriate check programs that conform to the first version of this recommendation.These programs make it possible to avoid the initial errors and their subsequent de-velopment to larger sources of problems, if they are used early and regularly enough.

Poor data quality can become a problem, especially in the case of a data exchangewhen this takes place between different CAD systems via neutral interfaces, or whenthis occurs between the same systems, however, with different levels of accuracy.This can lead to changes of geometry, loss of design requirements (e.g. positioncontinuity) or also to loss of geometrical or topological elements. Quite a few systemsuppliers therefore, rely on automatic repair mechanisms ("Healing") against situa-tions involving the import of bad/poor geometry. These mechanisms can be helpful,but are not recommendable for unrestricted/unchecked application, since they par-tially change or add new, possibly incorrect geometry.

Solution approach / Recommendation:

The recommendation endeavours to provide the definition of quality criteria, to makeavailable comparable check programs for as many CAD systems as possible andalso for neutral formats (especially STEP) and also to harmonise the accuracy andlimit values.The responsibility for the development of applicable design methods and for thetraining of the user lies with each individual business.

Within the focus of the CAD system suppliers, data quality at the present time is sub-ordinate or limited in respect to its influence over subsequent processes. This hasbeen proven above all by the results of the check programs during examinations ofthe generation and exchange routines.

Aimed at the system suppliers, this recommendation is an appeal for preferen-tial consideration with respect to the data quality, combined with the offer ofco-operation.

Only a co-operative, comprehensive initiative involving all the enumerated disciplinescan guarantee the data quality and reliably avoid the effort needed for rework/doublework or system constraints (OEM with respect to supplier).



2.1.2 Principles for Data quality

Product description, liability:Basis for work within the process chain will be the 3-D CAD data model instead of theconventional drawing.

The CAD model describes at each decisive stage the product which has to be pro-duced.

All aids required for the depiction of a product (physical models, Cax models, draw-ings, other graphical documentation) will be derived from a CAD model and shallcontain a remark indicating its CAD source (system name, version etc.).

The principle liability of 3-D CAD models and the fundamental conditions applying tothem are stipulated in the VDA recommendation 4950 “Agreement for the exchangeof CAD/CAM data“. The liability in the sense of the law will not be handled here, sinceit is a part of other contracts between the partners.

Complexity of the CAD model:An essential principle behind the generation of CAD models is to use as few and assimple geometrical elements as possible without thereby limiting the form or thefunction of the component part. “Simple” CAD models hold less problem potential forsubsequent processing and allow themselves to be more easily changed.

Engineering changes:The change services must take place on a CAD system according to scheduleddeadlines. The valid change status of the data must be recognisable and compre-hensible.

Depiction:The 3-D CAD data model describes the product in its real size (in the scale 1:1). 3-DCAD data models as well as associated derivations (e.g. drawings) must conformwith one another. (Exceptions: standard part geometry, table drawings.)

(Geometrical) Clarity:The CAD data model may not contain multiple/repeated definitions of geometry data(exact identical elements).

Structure:The CAD model structure and its documentation are essential quality criteria of CADdata.

Exchange scope:

The scope of the CAD/CAM data model which has to be exchanged must conform tothe requirements specified in the joint agreements.



Process chain:Various phases exist within the development and manufacturing process chainswhich place different requirements on the geometrical and organisational data qualityas well as on the scope of the data. These phases have a logical interrelationshipwith respect to their common end product (“parts that fall or are ejected from the pro-duction tool, or assemblies”). CAD data must be explicitly relatable to its intended usein the respective phases.

The process chain for “Automobile body sheeting” is a perfect example to illustratethis.Geometry design stage Process phase Intended use/ (acc. to Chapter. 2.2) Release

The contemplation and consideration of the complete process chain is extremely dif-ficult for the individual, since the particular process phases are often set-up with anindependent organisation and at several locations (i.e. affects several firms). None-theless, the individual should be aware of what bearing his contribution has on thequality and cost of the product, as well as on the success and the effort of the follow-ing stations. Therefore, the integration of the particular process phases must havepriority over the individual optimisation.

Continuity:Once started CAD process chains are not allowed to be interrupted.


Manufacturingprocess

quality control

CAD1

CAD1CAD2 / CAD3

CAD1

CAD1

Product release “Free for production”means “free for methods“ intool and plant manufacturing

Acc. to method acceptance (throughcustomer and generator) status:“Free for FM design” and“Free for NC programming”

Acc. to acceptance of casting blueprints(through customer and generator) status:“Free for generation of casting model”

Acc. to acceptance of casting model(through customer and generator) status:“Free for casting = casting”

Acc. to acceptance of the FM-design (through customer andgenerator) status:“Free for production”

CAD1CAD2CAD3

CAD1CAD2CAD3

Component /Product

Method

Production meansCasting blueprints

Casting model

FM designcompletion

Castingproduction

NC pro-gramming

By acceptance (through customer and gen-erator) of parts that fall/are ejected from thetool: “Free for delivery to the customer”


Design methodology:A design methodology describes the (systematic and recursive) procedure of theCAD user during the design of a component part/operation equipment. Quality prob-lems can be avoided from the start through appropriate design methodology. Thedesign methodology is, among other things, dependent upon the CAD system beingutilised.

Completeness:Completeness of a CAD model is on hand when the joint agreements concerning theexchange scope have been observed. On the other hand, this means that a completeCAD model can only be expected/demanded when an appropriate scope has previ-ously been stipulated.



2.2 Data categories

The categorisation of CAD data shall serve the purpose of classifying criteria andcharacteristics into a comprehensible and easily remembered group of 3-D CADmodels.

There are various approaches for a categorisation, i.e. the splitting up into “compo-nent parts” and “operation equipment” (for the production of components), in miscel-laneous process chains (dependent upon materials or of production methods), in“visible” and “non visible” parts, or conforming with the development stage (concept,agreements, release, detailing, etc.).

Here, the working group recommends a combined, “two dimensional” classification.

The columns describe the category of service requirements on the data quality; thelines describe the “design stage” of the geometry according to the process phases.

Geometry which is relevant to styling/design count as class A-category parts, i.e.“View” - Surfaces for body parts (metal und synthetic materials).

Function relevant geometry, such as frame parts or aggregate/major components,count as class B-category parts.

“Design stage of the geometry based on an example of the process chain “Automo-bile body sheet“:

Class A Class BZero geometry sharp-edgedCAD0Zero geometry radiusedCAD1Production geometry with worked in toler-ancesCAD2Production geometry subject to material andprocessCAD3


Zero geometry

Production geometry

Surface model withtheoretical edges

(sharp-edged)CAD0

Surface modelradiused

CAD1

Surface model withworked intolerances

CAD2

Surface modelsubject to

material and processCAD3


2.3 Geometrical data quality

The geometrical data quality provides information about how and with which ex-actness geometry elements shall be generated, so that the subsequent usability ofthis element within the process chain is possible.(A definition of technical terms can be found in the attachment.)

2.3.1 Wire geometry

Points, curves and lines are regarded as part of the wire geometry. They serve, forexample, as a geometry aid for the generation of faces and solids, as contours forNC programming as well as in drawings.

2.3.1.1 Tiny elements, tiny segments

Problem description: Elements, that fall short ofa particular size, by particular geometrical opera-tions (i.e. scaling, generation of offsets), by theexchange of data (in a system of lesser accuracy)or through further processing (NC) can lead to in-valid, degenerated elements and therewith togaps. The reworking of these elements mean aconsiderable increase in effort. These elementsoften occur involuntary not only through radiusingbut also through "closing mechanisms" duringbridging of small gaps or by overlapping.

Recommended solution: Make tiny elementssuperfluous through an appropriate extension (ex-trapolation) of the elements to be joined and de-lete, or respectively, enlarge the tiny elements andshorten correspondingly the elements to be joined.


Example: Tiny elements/segments


2.3.1.2 (By approximation) Identical elements

Problem description: By miscellaneous geometricaloperations or through copying external geometry intothe model, (approximately), identical elements canoccur that unnecessarily enlarge the space require-ments of the model and cancels out the explicitness ofthe element, i.e. the validity of this element. Identicalelements, also known as double elements, often im-pede the automatic recognition of continuous curvedlines or impede NC and FEM operations, for example.Also elements which lay completely in a larger elementare considered as identical.

Recommended solution: Deletion of one of the double elements. Thereby, it isimportant to take care as to which of the double elements shall be deleted.

2.3.1.3 Continuity

A curve path consists of one or more individual curves with, if appropriate, severalinternal sections (segments). Generally there are continuity requirements whichhave to be fulfilled on the borders of the segments and curves. These are positioncontinuity (G0), building upon that, tangential continuity (G1) and after that, curva-ture continuity (G2).

Position continuity (G0)

Problem description: The first and most importantcontinuity is the “Position continuity”, i.e. the transitionof curves and curve segments without gaps and/oroverlapping. A discontinuity of the position endangersfollow up operations that build upon the unity of curvepaths, especially after scaling and transfer within asystem environment of high accuracy.

Recommended solution: Position discontinuity are tobe rectified by limiting the affected curves to one an-other within the tolerances for identical elements. Apossible, necessary extension of one or both elementsby insertion of a small fill-piece (possibly a tiny ele-ment) is preferential.

Example: Identical elements


Example: Position continuity of curves


Position / Tangential continuity (G1)

Problem description: Tangential continuity(with specified position continuity) means thekink free transition of two curves without achange in the tangential angle. A tangentialdiscontinuity is generally visible and can befelt. In a fully rounded model this generallyoccurs unintentionally. At the same time,there can also be intentional design neces-sitated tangential discontinuities (e.g. cham-fers/bevels, character lines).

Recommended solution: Interactively cor-rect the curves by creating them anew withidentical tangential conditions or round offwith an additional curve with suitable tangen-tial specifications (i.e. round off two straightswith a radius).

Position / Tangential/Curvature continuity (G2)

Problem description: Curvature continuity(by a given position/tangential continuity)means parity of the curvature radius at thecontact point and thereby, the harmoniouscurvature transition of two curves. Curvaturecontinuity of curves are normally only re-quired by the contour description of compo-nent parts with special functions (cams,worms, etc.), or by stylistic elements.

Recommended solution: Replace the af-fected elements through elements with suit-able curvature conditions at the ends; e.g.neighbouring elements, which in each casehave constant curvatures (straight lines, cir-cles, etc.), shall be replaced through freeform curves.

Example: Tangential continuity


Example: Curvature continuity of a curve


2.3.1.4 Polynomial degree

Problem description: The degree of thePolynomial depiction for a curve segmentdetermines the number of degrees offreedom (variance) of a curve. The higherthe degree, all the more greater the com-plexity of the curve. Curves with highpolynomial degrees are susceptible forunintentional/unwanted curvature andtherefore, where appropriate, must be ap-proximated when changing to anotherCAD system, i.e. approximated within thebounds of a tolerance. In both cases, thisgenerally means a worsening of dataquality.

Recommended solution: High polyno-mial degrees (e.g. > 9 degrees) should beavoided. Practical experience has shownthat polynomial degrees up to 6 degreeshave proved to be the best. Unnecessarycurves should be meaningfully subdivided,i.e. dependent upon the curvature, individ-ual curves with smaller degrees.

2.3.1.5 Waviness in a planar curve

(Due to the upwards compatibility of the check programs this criteria has been adopted from ver-sion 1 of VDA4955; in the meantime, for practical purposes it barely has any meaning!)

Problem description: A waviness, i.e. a number ofalgebraic changes on the curvature of a free formcurve is often unintentional and perhaps critical forfollowing operations, e.g. by the generation of anOffset.

Recommended solution: Analyse the tangentialand restart point conditions of the curve and cleanup, or where necessary renew. Also, analyse thecreated faces of intersecting curves and correctwhere necessary.

Example: Polynomial degrees of curves

Example: Waviness planar curves


change of sign


2.3.1.6 Self penetration/intersection

Problem description: A self penetration/intersection(the existence of an intersecting point of a curve withitself) is in each case unintentional, i.e. it has no de-sign purpose. This error causes problems with othergeometrical operations, such as the generation ofoffsets or faces, as well as with NC programming.

Recommended solution: Self penetration resultingfrom faulty development of offsets (offset distance islarger than the inside radius), or projections (three-dimensional curves in oneplane) are to be avoided wherever possible. Retroactively regenerate the curvescorrectly!

2.3.1.7 Multiple knots

(For reasons of completeness this criteria has been included; meanwhile, in practice it barely hasany meaning!)

Problem description: A knot vector is re-quired for the definition of NURBS and B-Spline curves. This defines, amongst otherthings, the number of the curve segmentsand the continuity of the transitions be-tween the individual curve segments. Theknot vectors are defined through a seriesof real numbers. Individual knots can bepositioned on top of one another, this isthen called “Multiple-weighting of knots” orshort, “Multiple knots”. Curves with closeneighbouring knots can be changed intheir internal continuity characteristicsthrough knots coinciding with one anotherduring the transfer into another system en-vironment set with coarser tolerances!

Example of a knot vector of a NURBS-curve of 3 degrees:(0.0, 0.0, 0.0, 0.0, 0.3333, 0.3334, 1.0, 1.0, 1.0, 1.0)

Knot tolerance < 0.0001: - Curve consists of 3 curve segments,- internal segment transitions are G2 constant

Knot tolerance > 0.0001: - Curve consists of 2 curve segments,- internal segment transition is not G2 constant

Recommended solution: Generate curves anew with sufficiently large enoughknot clearances.

Example: Self penetration

Example: Multiple knots



2.3.2 Surface

Surface is the name given to the basis faces of acomponent part that can protrude beyond the actualcontours of the part. These faces are generallybounded through “simple” mathematical boundarycurves and usually serve as a surface for thebounded surfaces with complex edge curves.

Surfaces can be composed of several segmentfaces called “Patches”. These can be bound to-gether within the bounds of internal tolerances forposition and gradients. Depending upon the num-ber of segments (n, m) of the boundary curve, asurface is formed from a group of (n) times (m)patches.

2.3.2.1 Tiny elements, Tiny segments

Problem description: Faces or face patches whichfall short of a particular extent in at least one pa-rameter direction, can result in degenerate, defectiveelements by changes in the system or in the toler-ance range, or lead to gaps in the topology throughtheir suppression or deletion.The reworking of these elements require a consider-able effort.

In addition, tiny elements raise the storage requirements, the effort required tomake changes and duplicates the dangers of continuity problems. They often oc-cur through system automation without the user even wanting it. The automaticclosure of gaps in the case of data importation from foreign systems is alsoamongst the causes.

Further, it is applicable that the length relationship oftwo neighbouring segment edges (one parameter di-rection within a surface) should not be smaller than1:100 (“relative patch size”) for facepatches/segments. Such size ratios are a sign of poorpartitioning and increases the effort required to makechanges.

Recommended solution: Tiny elements should beavoided or made superfluous through suitable en-largement and divisioning of the neighbouring ele-ments and then subsequently deleted.

Example: Surface with boundedsurface

Example: Tiny element/segment


Example: relative patch size

Edge curves

n x m Patches


2.3.2.2 Tiny segment edge

Problem description: A Face segment (Patch) withexact one segment edge below a tolerance (“quasi-triangular patch”) can lead to non defined normals inthe case of a change in the system or tolerancerange.

Recommended solution: Take care manually forsegment edge sizes larger than the tiny element tol-erances or describe by means of a three sided,bounded face.


Problem description: Identical/Double ele-ments unnecessarily increase the storage re-quirements and cancel out the explicitness,i.e. the validity of these elements. They ob-struct the handling of these models, e.g. theautomatic creation of the topology. It is under-stood that elements which lie within one largeone are also identical.

Recommended solution: Delete doubleelements. Thereby, ensure that “the required”element is retained.

Example: Tiny segment edge


Example: Approximation of ident. surfaces


2.3.2.4 Continuity

Problem description: Similar to the conti-nuity of curves, the position / tangential / andcurvature continuity of surfaces are of con-siderable importance for their qualities asbasis geometry (i.e. for bounded surfaces orintersection curves). Since surfaces gener-ally protrude beyond the actual contours ofthe part and therefore, transitions from sur-faces into the edge do not or only seldomexist, only the continuity of the face seg-ments (patches) by naturally bounded sur-faces will, therefore, be examined and noted.

Recommended solution: Naturally bounded surfaces with discontinuity of thepatches must be corrected or newly generated via suitable fundamental condi-tions.


Problem description: The degree of thepolynomial depiction for every patch deter-mines the number of degrees of freedom(variance) of a face. A too high polynomialdegree can lead to oscillations, or in thecase of a reduction in the degree throughapproximation, to a deterioration of the dataquality with respect to faithfulness of form,storage requirements and continuity.

Recommended solution: Avoid high poly-nomial degrees (i.e. > 9) wherever possible.Avoid unnecessary complex surfaces orsensibly divide them, for example, into indi-vidual surfaces with smaller degrees de-pendent upon curvature. Practical experiencehas shown that polynomial degrees up to approximately 6 degrees have proved tobe the best.

Example: Position continuity

Example: Tangential continuityExample: Position continuity Example: curvature continuity


Example: Polynomial degree of surfaces


2.3.2.6 Waviness

(Due to the upwards compatibility of the check programs this criterion has been taken over fromversion 1 of VDA4955; at the present time however, in practical operation it is graphically interac-tively checked!)

Problem description: An unintentionalcurve trend of a surface is possibly critical forthe styling and following operations such asfor example, NC processing.

Recommended solution: Correct surface orgenerate anew with suitable fundamentalconditions (degree, edge curves or restartpoints).

2.3.2.7 Minimum curvature radius

Problem description: In order to guaranteethe ability to mill a face, the curvature radiusof a face must not fall short of the givenminimum at any position, as otherwise le-sions can occur on that face during the workprocess (milling). The minimum curvature ra-dius of the face also limits the maximumclearance of an Offset face.

Recommended solution: Faces, which re-main under the given minimum curvature ra-dius, must be created anew, e.g. through ap-proximation or smoothing.

Example: Waviness

Example: minimum curvature radius



2.3.2.8 Angle between the boundary curves of surfaces

Problem description: If the angle betweentwo neighbouring boundary curves of a sur-face are less than the minimum angle ormore than the maximum angle, this can re-sult in undefined normals in the cornerpoints.

Recommended solution: The surfaceshould be divided (e.g. star-shaped from thecentre of the surface in 3 faces) or enlargethe surface and generate the required areaas a face.

Should it be the case that, despite a criticalangle, the normals on the edge of the faceand in the corners are defined, then thesecases can be ignored if the recipient of thedata is in agreement.

2.3.2.9 Reversal of normals

Problem description: Generally, the normalvectors of a surface are shown uniformlyfacing either into the component or out of itin every one of their points. Occasionally,deviations from this behaviour have beenascertained at the edge of surfaces, throughwhich, for example, damage to the workpiece can occur, since the tool can cut intothe face.

A special case of the folded down/flippedover normal at an edge can often be foundat the tip of a “quasi” triangular patch. This isespecially the case when two boundarycurves, which are diverging upon a point,slightly project beyond the point of intersec-tion.

Recommended solution: Faces, where thevectors for normals have been turnedaround, should be newly created (under spe-cial consideration of the tangential conditionsat the periphery). In the case where a vectorat the tip of a triangular patch is flipped or turned around, the tip (within the boundsof admissible gaps and tiny elements) can be "cut-off", so that the new, fourthedge of the patch receives an admissible length. Alternatively, a three sidedbounded face with correct normals can be generated.

Example: Angle between edge curves

Example: Reversal of normals



2.3.2.10 Patch numbers/ partitioning

Problem description: An unreasonable, highnumber of patches within a surface is generallya sign of unfavourable complexity or size of asurface. This occurs, for example, through apoor approximation of a face of higher degreeto that of lower degree, or through the amal-gamation of areas with completely differentcurvatures in a face

Recommended solution: Partition surfaceswith large curvature differences. A surface withharmonic curvature distribution and a largenumber of (smaller) segments can be replacedwhere necessary through surfaces with mean-ingful, higher degrees.

2.3.2.11 Unoccupied Patch Rows

Problem description: The area of a facewhich is occupied by a bounded face can, inindividual cases, be so small that whole rowsof patches are unoccupied. These unoccupiedpatch rows unnecessarily use up valuablestorage space and generally can be erasedwithout any problem.Via this criterion, the surfaces which do notserve the purpose of defining bounded sur-faces and therefore are most likely to be su-perfluous, will also be found.Sometimes the unoccupied face domains arestill required in subsequent process steps.Their reconstruction is then time consumingand only approximately possible. For this rea-son, no general recommendation will be madeconcerning the elimination of unoccupied patchrows.

Recommended solution: If required, divide the surface along an appropriatepatch border and delete the superfluous part: Delete completely unoccupied sur-faces entirely.

Example: Patch distribution

Example: unoccupied patch rows




(For reasons of completeness this criteria has been included; in the meantime, for practical pur-poses it only has any meaning in special cases with respect to the exchange of data!)

Problem description: As is the case forNURBS and B-Spline curves, a knot vectorfor every parameter direction will be re-quired for the definition of NURBS and B-Spline faces. These define the number ofthe face segments in the parameter direc-tions u and v and the continuity of thetransitions between themselves. The knotvector will be defined through a monotoneseries of real numbers. Individual knotscan also be identical, these are known as“multiple weighting of knots” or simply”multiple knots”.

After transferral into another system envi-ronment with coarser tolerances, it is possi-ble that close neighbouring knots can beidentical there and consequently, the internal continuity within the face can bechanged in an undesirable manner!

Recommended solution: Generate faces anew with a larger and thereby possi-bly smaller form change, or, if appropriate, delete.

Example: Multiple knots



2.3.3 Bounded surface (Face)

Clearly defined faces, also called “Bounded surface“ or simply “Face“, describe thegeometrical surface of an object, if appropriate, inclusive of holes, indenta-tions/recesses or similar, on the surface that forms the basis with the (randomcomplex) boundary curves which are projected upon it. It is understood that theboundary curve is an endless continuous curve.

This association between surfaces and bounded surface leads to the fact that agreat deal of quality criteria are principally applicable for both and are here nolonger accounted for (polynomial degrees, curvature, internal continuity), or corre-spondingly, must be applied to the bounded surface (tiny elements, identical ele-ments). Additionally, special criteria are applicable for the edge curves of thebounded surface.

Tiny elements

Problem description: Faces, which fall short of aparticular dimension, can lead to invalid, degener-ated elements and thereby to gaps, especially withcertain geometrical operations (e.g. scaling forma-tion of offsets), during the exchange of data (in asystem with inferior exactness), or by subsequentprocessing (NC) The reworking of these elementsmeans a considerable increase in effort is re-quired. These elements occur often unintentionallythrough radiusing.

Recommended solution: delete minimal boundedsurface or enlarge and adapt the neighbouringelements accordingly.

Tiny edge curves

Problem description: The boundary curves of abounded surface are generally made up of severaledge curves. Edge curves which fall short of a par-ticular dimension, can lead to invalid, degeneratedelements especially during the exchange of data (ina system with inferior exactness). Because of this,the bounded surfaces, as well as perhaps any topol-ogy which is on hand can be lost.

Recommended solution: Consolidate the edgecurves with bordering edge curves for a newbounded surface, or delete/enlarge the tiny edgecurves and rectify the connecting elements appropri-ately.

Example: Tiny bounded face

Example: Tiny edge curve



2.3.3.3 Continuity of boundary curves

Problem description: In the case of a discontinuity ofboundary curves, gaps and overlapping of their seg-ments lead to difficulties during the definition of thebounded surface, while angle of bends and curvatureleaps can, for reasons of design, be intentional.

Recommended solution: Newly demarcate the endsof boundary curves to one another within the tolerancesfor identical points. Thereby, the adaptation of thecurve end is preferential to inclusion of tiny segments!

2.3.3.4 Penetration or contact of boundary curves

Problem description: Penetration or contact ofboundary curves, caused by using values lower thanthe minimum distance tolerance, can lead to invalidfaces (loss of face definition) and to loss of integrity ofa topology by a change in the tolerance environment.This criterion covers the penetration/contact of ex-tremities with extremities, extremities with inner and in-ner with inner boundary curves.

Recommended solution: Enlarge the space betweenboundary curves, remove loops and, where necessary,partition faces or consolidate boundary curves.

2.3.3.5 Proximity of boundary curve to surface

Problem description: Boundary curves with too largea distance to the surface (normal or laterally) preventthe correct definition of the bounded surface. They re-quire that the projection onto the surface be per-formed once more in systems or environs of greaterexactness.

Recommended solution: Create curves, that are al-ways within the range of tolerances of identical ele-ments, as sectional curves or projections, or wherenecessary, generate anew.


Example: discontinuity ofboundary curves


Example: Penetration/contactof boundary curves external-internal

Example: Proximity of boundarycurves to surface


2.3.3.6 Parallel path within a boundary curve

(For reasons of completeness this criteria has been included; in the meantime, for practical pur-poses it barely has any meaning!)

Problem description: Boundary curves thatare not parallel can lead to unwanted selfpenetration and face degeneration in somesystems,.

Recommended solution: If necessary, par-tially reverse the direction of rotation and rec-reate bounded surface.

2.3.3.7 (Proportional) Number of segments in boundary curves

Problem description: An unproportionallylarge amount of segments within a boundarycurve raises the risk of tiny elements as wellas discontinuity and impedes makingchanges.

Recommended solution: Correct or replaceboundary curves and recreate the boundedsurface with them.

Example: Direction of rotation ofboundary curves

Example: Segment distribution ofboundary curves



2.3.4 Composite surface / Surface group, topology

Neighbouring, bounded surfaces, which together form a particular part or completesurface of an object, are called composite surfaces/surface groups or topology.Within a topology, special requirements apply regarding the faces in the boundarycurves:

2.3.4.1 Continuity

Problem description: In accordance withthe definition, bounded surfaces and theirassociated formations describe the surfaceof component parts and operation equip-ment. Thereby, the continuity of the boundedface has a special significance among eachother.

Position continuity, i.e. “continuous” transi-tion of bounded surfaces within a topology isthe most important quality characteristicwithin every surface group. A permissiblediscontinuity that is within the bounds of thetolerance, can lead to a loss of the topologyin the case of a change in the system or inthe range of tolerances, or can cause somesystems to perform an automatic correction(Healing). Because of this, unintentionalchanges or new (tiny-) elements can occur.

Tangential or curvature discontinuity could have an effect on the ability to mill theobject or on the surface quality.

Recommended solution: In the case of gaps by face transitions, the affectedfaces should be generated anew with common boundary curves. Thereby, thefundamental conditions for tangential or curvature continuity must be observed.

Example: Position continuity



2.3.4.2 Junctions

Problem description: It is important for the topological ex-plicitness of a surface that every inner face edge must haveone explicit neighbouring face, i.e. may not have more thanone neighbouring edge and thereby is free from bifurca-tion/junctions. It is however admissible that a face edgeborders on several neighbouring face edges one after theother (“T-type butt joint”).

Recommended solution: Remove superfluous faces.

2.3.4.3 Alignment/orientation of similar normals

Problem description: The uniform orientation ofthe face normals within a topology is necessary, forexample, for the determination of machining direc-tion by milling, for hatched depictions, as well as forascertaining through the geometry the capability forejecting the part from the tool, or for the definition ofthe touch direction by measuring.

Recommended solution: Where necessary, “re-version“ of individual face normals so that all facenormals are topologically uniformly oriented, i.e.“away from the material“.

2.3.4.4 Knife edges

Problem description: If the angle of the tangentialplanes between neighbouring bounded surfaces onthe common edge is too small, then sharp edges orrecesses occur. Such areas are not realistic andcannot be produced. They arise, for example,through subtraction of a cylinder from a cube

Recommended solution: check the design


Example: T-butt joint

Example Orientation of normals

Example: Knife edge


2.3.5 B-rep solids

2.3.5.1 General criteria for B-rep solids

Problem description: By the transfer of solids via neutral interfaces (e.g. STEP) aso called B-rep (Boundary representation) will be transferred. This is, as the namealready indicates, the description of the solid through its bounded surfaces (Faces)which represent the direct surface. These faces lay the basis for surfaces andboundary curves. Hence for solids, the quality criteria for a closed (unified) groupof faces are also applicable. The criteria 2.3.2 till 2.3.4 are correspondingly appli-cable for the bounded surfaces of a solid, inclusive its surfaces, and boundarycurves, i.e. distance of bounded curves to the surface.

Recommended solution: See under 2.3.2 to 2.3.4. During the correction of sol-ids, care shall be taken to ensure that an enclosed group/association of faces re-mains preserved.

2.3.5.2 Tiny elements

Problem description: Solids, which fallshort of a particular dimension in two direc-tions in space, should be avoided. Depend-ent upon the interface and the system inter-nal parameter for the degree of accuracy,these elements can cause problems or belost during the exchange of data. Often,these elements may also occur unintention-ally during the modelling process (i.e. inter-section of two solids, which only slightlypenetrate each other) and are not able to beproduced.

Recommended solution: When the system parameter is adjusted and correctlyset up to the receiving system, then an error message/warning should appear al-ready during modelling if these tiny solids are generated due to intersec-tion/overlapping or penetration. This error source can be eliminated most simplythrough displacing or enlarging the affected elements. If appropriate, remove tinyelements entirely, or make superfluous by enlarging the neighbouring elementsand the tiny elements can then be deleted.

Example: Solid tiny element



2.3.5.3 Distance Vertex - Edge

Problem description: B-rep solids consistof the topological elements Vertex, Edgeand Face, which are assigned to the geo-metrical elements Points, Curves andBounded surface.The point which belongs to a Vertex mustlie within a stipulated tolerance on thecurve which is a part of the correspondingedge. Should the distance between thepoint and the curve exceed this value, thenthe solid is defective.

Recommended solution: If possible, project the point onto the curve, otherwisegenerate anew.

2.3.5.4 Distance Vertex - Face

Problem description: The point which be-longs to a Vertex must lie within a stipulatedtolerance on the associated bounded sur-face. Should the distance between the pointand the face exceed this value, then thesolid is defective.

Recommended solution: If possible, proj-ect the point onto the face, otherwise gener-ate anew.

Notice: The distance Edge - Face will already have been checked through the cri-terion 2.3.3.3 “Proximity of boundary curve to surface”.

Example: Distance Vertex - Edge


Example: Distance Vertex - Face


2.3.6 Drawing elements


Problem description: Drawing elements that fall short of a particular measurecan lead to invalid elements, due to degeneration, during the exchange of datainto a system environment of lesser accuracy.

Recommended solution: Delete tiny elements. Should dependent elements (di-mensioning, hatching) be on hand, these should be isolated prior to the deletion.


Problem description: It can happen that during the generation of a drawing,identical elements can unintentionally arise (i.e. several lines of varying or equallength over one another) which unnecessarily enlarges the space requirements ofthe model. Identical elements, also called double elements, often hinder, for ex-ample, the automatic recognition of continuous curve paths.

Recommended solution: Delete identical elements. As long as the elements areexactly identical they can be deleted without any problem. Where several ele-ments of varying length lie above one another, then, under certain circumstances,it is more meaningful to discover the longest element and delete the shorter ones.

2.3.6.3 IGES conformable texts

Problem description: During the generation of texts and dimensioning, specialcharacters and mutated vowels (Umlauts), as well as “ß” can lead to transferralproblems. A too high number of text characters (>70 per line) as well as multi-linetexts can lead to losses during transfer and are for that reason to be avoided orrespectively, a special agreement reached concerning the problem.

Recommended solution: Special characters and vowel mutations (Umlauts), aswell as “ß” are to be replaced (e.g. ä through ae; ß through ss). Texts with morethan 70 characters shall be split up into several individual texts. Multi line textsshall be replaced by several single line texts.

2.3.6.4 Polynomial degree / order

Problem description: Curves with high polynomial degrees must, where neces-sary, be approximated during a change-over to another CAD system, i.e. approxi-mated within the bounds of a stipulated tolerance and perhaps divided up. If it isthe case that the receiving system is only able to process curves with a particularmaximum polynomial degree, it is possible that these curves could be falsely in-terpreted or ignored.

Recommended solution: Compare polynomial degree of the curves with givenmaximum value and, if appropriate, approximate through a curve of lesser degree,however with more segments, under consideration of the specified tolerance.

Chapter 2: Data qualityChapter 2: Data quality


2.4 Organisational data quality

In the case of criterion concerning the organisational data quality, a “recommen-dation” for the implementation will be given instead of a “proposed solution”.

2.4.1 Administrative information / Model name

Problem description: There is a requirement for the exchange of administrativeinformation (e.g. change index, change description, material information, releasestatus, release date, generator, project, etc.). The model name can contain limitedinformation concerning contents and status.

Recommendation: The model name should fulfil a stipulated convention. It caninclude for example component/project numbers and designation, data type,change index, release date generator, etc.Further administrative information can be agreed upon and attached to the CADmodel in other suitable and transferable forms.

2.4.2 Model structuring

Problem description: The model structuring is an essential prerequisite for theclarity of the CAD 3-D data model. It allows the safe and speedy reduction of themodel contents to a useful exchange scope.

Recommendation: The model structure shall fulfil the following requirements:

• It must be recognisable, comprehensible and firmly allocated to the CAD datamodel,

• It must be supplied with the data in accordance with the rules concerning dataquality documentation during the exchange of said data.

• It should be able to differentiate between auxiliary geometry and essentialproduct geometry (i.e. wire, face and solid geometry),

• It should be able to differentiate between right / left / centrical areas of the ge-ometry,

• It should be able to reproduce logical relationships such as functions, assem-blies or similar,

• It should be able to differentiate between changeable and non-changeablecontents.

2.4.2.1 Coordinate system(s)

Problem description: In order to guarantee an explicit spatial association, CADgeometry’s shall be transferred in relationship to a stipulated coordinate system.

Recommendation: The binding standard reference is, for example, the vehicle orengine coordinate system, dependant upon part.



Additional coordinate systems are allowed (e.g. for tasks pertaining to productionor quality assurance). Should the geometry be transferred to one of these coordi-nate systems, then its relationship to the reference coordinate system must be ex-plicitly documented and capable of being exchanged over interfaces.

2.4.2.2 Changes

Problem description: The speedy and complete recognition of changes is of ab-solute importance for the recipient. In contrast to the drawing sector, for 3-D mod-els there are no standardised identification methods and elements. Because ofthis, it is all the more important that a mutual agreement is reached between thepartners concerning an applicable identification procedure before the transfer ofdata.

Recommendation: A description of the changes shall be delivered with the data.The position of the change shall be identified (e.g. colour, layer structure, etc.).Ensure that the transfer of the identification marking can take place with a neutraldata format. The changes shall be integrated into a complete component part, i.e.not only the changed geometry shall be transferred. Every approved and releasedchange shall receive a new change index. This index shall conform to that of theassociated drawing. Change or release status respectively, shall be recognisablein the model name.

2.4.3 Drawings

In this position, performance criteria shall be described which affect especially thegeneration of CAD drawings as technical documentation.

2.4.3.1 Views

Problem description: In order to allow the recipient to perform subsequent workwithin the system, beyond just the plotting function, there are particular rules whichare to be observed during use of the structure element “View”.

Recommendation:• The view frames (vertical boundary level) have to be within the drawing frame.• Drawing elements shall be generated in the “view”, inwhich they are depicted.• Views with detail sections / enlargements have the same source (zero point,

reference point) as the original view.• Views can be scaled; the geometry itself however may not be scaled!

2.4.3.2 Referencing of 3-D models in drawings

Problem description: A number of CAD systems (i.e. CATIA V4 “Transparency”)allow the building up of drawings without a separate 2-D geometry through projec-tion of the 3-D geometry in the drawing plane.



Recommendation: At the beginning of a project the partners involved shouldreach a mutual agreement as to whether the drawing shall consist exclusively oftrue drawing elements or whether views shall also be allowed on the 3-D model. Inboth cases, the 3-D CAD model is binding for the exact description of the compo-nent part. Discrepancies between the 3-D CAD model and the drawing are implic-itly to be avoided.

2.4.3.3 CAD source notice

Problem description: Drawings (e.g. Plots) often contain no reference concern-ing their CAD source data record. Because of this, the feedback of changes (e.g.in the tool manufacture) to the 3-D CAD model is made all the more difficult.

Recommendation: Drawings must include a CAD source reference (name ofsystem, version, storage address 3-D CAD model, part / drawing index etc.).

2.4.3.4 References on external data bases and libraries

Problem description: During the exchange of geometry’s, symbols, etc. fromexternal libraries, the visibility/usability of such by the recipient shall be assured.

Recommendation: By the utilisation of, for example, symbols, drawing frames orstandard parts from external data bases either• an explicit reference regarding the existence of such references shall be given

and the exchange of the library shall be discussed or• assure the complete disbandment of this structure.

2.4.4 Solids

2.4.4.1 Capability for regeneration

Problem description: Solids will not always be brought up to date in a number ofsystems, rather they must be explicitly regenerated. Solids that are not capable ofbeing regenerated, cannot be processed further. Should the solid not be in a re-generated condition, then it could be that modifications have been carried outwhich possibly have not yet been taken into consideration in the build up of themodel.

Recommendation: The regeneration of the solid shall be carried out in the sys-tem that was used to generate the solid. Where necessary, error mes-sages/warnings that appear, or the automatic suppression of incorrect operations,shall be carefully checked and, through suitable measures, eliminated or respec-tively, avoided.



2.4.4.2 Derivability of other geometrical forms

Problem description: It is important to be able to derive other geometrical formsfrom solids during the design process and in the process chain. A prerequisite forthis is the capability for faultless regeneration.

2.4.4.2.1 Edges / individual faces

Problem description: The derivation of edges and individual faces of a solid willbe required during the whole design process. It often forms the original or auxiliarygeometry for further designs.

2.4.4.2.2 Closed (encompassed) surface groups

Problem description: The derivation of a closed surface group is often necessarywith an exchange between different CAD/CAM systems. The surface depiction isjust as much required for CAD/CAM systems which are not able to process solids.

Recommendation: Should it be the case that other geometry forms (2.4.4.2.1 and2.4.4.2.2) could previously not be derived, then it is quite probable that this is dueto errors that occurred during generation which must be found and corrected.

2.4.4.3 Development of solids

2.4.4.3.1 Preference for canonical elements

Problem description: If it is possible to describe a geometry through canonicalelements (e.g. a cylinder, cube, sphere, torus, profile or a rotational solid with ca-nonical contours, i.e. contours that are configurated for example out of arcs of acircle and straight lines), this depiction best fulfils the design requirements. A solidwhich has been generated in this manner is generally much easier to modify.

Recommendation: Critically check solids and their generating contours as towhether canonical elements have actually been used wherever this was at all pos-sible. Where necessary, replace non canonical elements with canonical ones.

2.4.4.3.2 Preference for form features

Problem description: The technology of the form feature comprises the descrip-tion of the geometry and in addition, includes its constructive significance (e.g.bore instead of cylinder). This can also include technological parameters (e.g.material data). Form features simplify changes and make the development of themodel more understandable.

Recommendation: Critically check solids as to whether form features have actu-ally been used wherever this was at all possible, if appropriate make up for this.



2.4.4.3.3 Preference for solid functions by hybrid models

Problem description: Many CAD/CAM systems offer the possibility to convertface models into B-rep solids. By this procedure, a solid body is formally created,however, this is not so easily modified in comparison to one which is configuratedfrom features or base solids that are controlled by parameters.

Recommendation: Critically check solids as to whether solid functions have actu-ally been used wherever this was at all possible, if appropriate make up for this.

2.4.4.3.4 No bypassing of the history

Problem description: Often a history is required for later modifications on solids(“History of origin”).

Recommendation: The subsequent inclusion of a “History of origin” is not possi-ble. The deletion of a history is therefore strongly to be avoided.

2.4.4.3.5 No utilisation of superfluous (auxiliary) geometry

Problem description: Elements that do not contribute anything to the geometryreduce the transparency, can lead to problems during the execution of modifica-tions and unnecessarily increase the amount of data.Unnecessary geometry is for example:• Auxiliary geometry “without children” i.e. geometry that is not required for the

development of solids,• A body will be completely taken up by a second one,• A body lies outside of a second one and will therefore be subtracted from it,• not utilised, faded out design steps (e.g. ”dead branches”).

Recommendation: Solids and their generating contours shall be critically checkedto determine whether only the necessary geometry for the design is on hand.Where appropriate, delete auxiliary geometry.

2.4.4.3.6 No (unintentional) cavities

Problem description: A solid should not include any unwanted cavities. Cavitiesoften occur unintentionally during modelling, they make the solid unnecessarilycomplex and increase the amount of data. Also, intentional cavities could possiblybe irrelevant for the recipient of the data (for model section analysis, for example).

Recommendation: Critically check solids to determine whether any unwantedcavities are on hand and, where appropriate, delete.



2.4.4.3.7 Systematical development

Problem description: Through a systematical development of the solid manyquality problems could be avoided. In addition, the data model would be easier tomodify.

Recommendation: Right from the beginning, solids should be structured and builtup systematically.

2.4.4.3.8 Reduction of the degree of detailing (Features)

Problem description: It can be meaningful to remove certain operations from thesolid (e.g. remove all filleting and all form bevels/slants) in order to perform instal-lation analyses, FEM calculations or a reduction of the data quantity. This shouldaccordingly be taken into consideration during the development of the solid.

Recommendation: Where necessary the solid should be appropriately modified.

2.4.4.3.9 Multi-body solids

Problem description: In the case of a number of CAD systems, solids can con-sist of several bodies, i.e. a solid consists of a collection of at least two disjunctivebodies (not touching each other). These so called multi-body solids cannot behandled by all CAD systems and are therefore to be avoided.

Recommendation: The individual bodies should, in each case, be converted intoan individual solid, e.g. in that one cancels/undoes the unification operation. After-wards, one solid will exist per body. This will occur automatically during a transfervia STEP.

2.4.4.3.10 Multi-solid parts

Problem description: A part is defined here as a CAD file at operating systemlevel. A number of CAD/CAM systems can not handle several solids in one part,but expect in each case only one solid per part. This can lead, for example, toproblems during the exchange of data should one want to transfer complete as-semblies.

Recommendation: In each case, the individual solids should be stored in a sepa-rate part. Assemblies will be transferred as a consolidation of individual parts.



2.5 Additional agreements

2.5.1 CAD system parameter for exactness / tolerances

Problem description: System parameter, as well as the concept of their utilisa-tion and influence, control the mathematical algorithm of CAD systems and deter-mine therewith the characteristics of the geometrical elements such as:

• Identity• contact / connection / continuity• unity

These characteristics, on the other hand, have an immediate influence on thetransfer results, i.e. the success of the transfer during the exchange of data.

For a better understanding of the recommendations at the end of this chapter ashort description of the essential exactitude parameters and strategies will be pro-vided in the following sections.

2.5.1.1 (system neutral) Definition of the exactness parameter

The following listed parameters (with various designations and values) for mathe-matical operations are used in all known CAD systems. Some systems establishthe minimum element size and the maximum gap via the same parameter. Not allsystems allow or recommend the manipulation of the parameter through the user.

minimum element size: describes the extent of the smallest element which canbe imported or generated from a random geometrical operation,maximum gap: describes the maximum distance between elements, up to whichunity or uniformity of geometrical or topological elements will still be adopted (e.g.gaps between curve sections of an endless curve or between a solid edge and theassociated corner point).maximum model size: Describes the extent of the largest element or the greatestdistance between two elements which can be generated or imported from anygeometrical operation. Dependent upon the CAD system, these sizes will be inter-preted in the coordinate system as extent and also as position (coordinate).Maximum angle: describes the maximum authorised angle between two vectors,up to which parallelism or tangency will still be adopted.



2.5.1.2 Accuracy strategies / philosophy

The major portion of CAD systems that are employed in the automobile industrythroughout the world are based on at least one of the following accuracy concepts:

Relative or dynamical tolerance: Accuracy is continuously adapted by the sys-tem. Thereby, for example, the smallest element or the largest gap is in proportionto the greatest model expansion. Should the component part grow, then the small-est element that may be generated will grow correspondingly and the allowed gapalong with it. Thereby, the development (reduction) of the accuracy is unidirec-tional, i.e. non-reversible. Small elements that were allowed at the beginning of thedesign will later possibly not be allowed, even if a large element, that has beengenerated in the meantime, will be deleted again (e.g. Pro/Engineer during theadjustment for relative accuracy).Adjustable absolute accuracy: A constant accuracy that can be adjusted withinthe system by the user at the beginning or also during modelling. Thereby, thesmallest element, the largest gap, as well as any further parameters will be de-fined, with a corresponding effect on the maximum size (e.g. CATIA V4, CADDS5,Pro/Engineer when adjusted to absolute accuracy).Fixed absolute accuracy: An accuracy that is fixed within the system and whichcannot be adjusted by the user (e.g. IDEAS).Tolerant accuracy: Thereby, an absolute accuracy will be set by the user; how-ever, from case to case, that means for example, from boundary curve to bound-ary curve, various rough accuracy’s can be “tolerated” without the geometrical ortopological element becoming invalid. (e.g. Unigraphics and other CAD systemswhich are based on the parasolid core).

2.5.1.3 Results of the accuracy investigation

A VDA/ProSTEP team gathered the following experience during a joint project withvarious system suppliers entitled “Examination of the effects of the exactitude con-cept and the value on modelling and the exchange of data”:(See chapter. 4.1 for information sources regarding the results and individual test scopes)

Results with respect to modelling:(of a Solid with diverse, sometimes extremely small elements and curvatures)

In all four CAD systems which were investigated, it was possible to generate thetest part with absolute accuracy, with a value of accuracy below the smallest ele-ment.

During the ensuing internal check it was discovered that the least modelling prob-lems and the lowest amount of errors occurred when the smallest accuracy toler-ance for minimum element sizes and maximum gaps was chosen.

The study concerning the effects of these values of accuracy on the maximummodel size was, up until now, not carried out, but is being planned.



Results with respect to the exchange of data:

With the employment of similar CAD systems, the exactitude problem reduces it-self to the use of different values of accuracy. In neutral interface formats, eitherthe specification of the various/dynamic exactitude parameters are not possible(IGES, VDAFS) or their correct application/evaluation is not guaranteed (STEP). Acheck or revision of the STEP standard as well as an appropriate extension of theSTEP processor tests are being planned.A valid Solid can be transferred with every system pairing using the following pro-cedure: 1. Modelling with absolute accuracy (e.g. ½ times the smallest designelement), 2. Output of this value in the STEP file (UNCERTAINTY _MEASURE _WITH_ UNIT) and 3. Reading-in of the STEP file with this modelling value.On the other hand, it has been determined that in only one case was it possible totransfer a valid solid using the standard procedure, (Standard procedure: 1. Mod-elling with standard accuracy (with this test part, sometimes impossible to createerror free), 2. Output of the calculated exactitude in the STEP file, 3. disregard ofthis exactness and instead, reading-in own standard exactitude).

Resulting recommendation:

The usage of absolute accuracy (if this is possible) is recommended to the usersof all CAD systems when modelling,

The users of CAD systems with "tolerant modelling" are recommended to utilisethis possibility only up to the agreed “inexactitude”.

The value of the accuracy to be set should orientate itself according to the follow-ing formula. Automatically generated elements (which, for example, are causedthrough miscuts or miscurvatures) orientate themselves automatically on the sametolerance, but most certainly must be regularly examined and if appropriate,should be corrected.

Tolerance value = smallest to be designed element size / X(X=2 till 12, dependent upon CAD system; In test: Tolerance = 0,004 to 0,01 mm with 0,02 assmallest element)

The data exchange partners should stipulate an appropriate tolerance value withinthe framework of the data exchange agreement (see form in attachment 3),

The issue of this value in neutral format shall be guaranteed,

and/or the Import of CAD data from external "foreign" systems with this agreedvalue shall be guaranteed.

One should implicitly refrain from making any (temporary) change to the tolerancevalue (variable accuracy) in order to set the CAD system up to be "toleranter" for acritical operations.



2.5.2 Data quantities

An agreement shall be reached between the exchange partners concerning themaximum exchange file size (measured in megabytes), the interface format aswell as the choice of the data carrier.

2.5.3 Version of CAD system

Especially by the exchange of native data, the version status of the CAD systemutilised must be agreed between the partners. A change in the version must beannounced as early as possible (several months prior).

2.5.4 Technological information

Problem description: Technological information, among these, for example, fall,material, surface, quality, tolerance or assembly information, are, similar to that ofthe change information, at the present time not standardised in 3-D CAD datamodels.

These types of technological information are, however, often a component part ofthe CAD model.

Recommendation: Provided that they are not immediately, explicitly and transfe r-ably linked with the geometry, then they are to be depicted in the drawing.

2.6 Data scope

It is essential to conclude an agreement to satisfy the demands for an adequateand necessary information obligation in the individual phases of a process chain.This agreement is essential for the determination of the data scope. Amongstother things, it should define the geometry, the description, the design stage andshould set the degree of details for the associated geometry as well as for miscel-laneous documentation (drawings).

Important here are the details with respect to the intended use. They describeswhether the exchanged data record depicts a piece part, a model section for thepurpose of analysing function/layout, an assembly (ZSB) or similar.

A form has been drafted for the support and documentation of this agreement (seeattachment 3).

2.6.1 Scope of 3-D CAD data models

2.6.1.1 Depiction of the material side, inside / outside

Problem description: In some departments of vehicle and component develop-ment not all upper surfaces/material sides will be depicted (e.g. by constant mate-rial thickness).



Recommendation:In this case, the direction of material to a designed face has to be identified at asuitable place through a line (vector) normal to the face. The line length, for exam-ple, shall be 100 times the material thickness and shall point in the direction of thematerial. For better clarification it is recommended that a text and sectional view isadded.

The partners have to come to an explicit agreement regarding which side is to bedesigned.

2.6.1.2 Filleting/chamfers

Problem description: The execution of filleting on a 3-D CAD model has sub-stantial influence on the effort (time) expended for generation and modification, aswell as on the size (in MB).

Recommendation: In surface modelling, all radii and chamfers that influence theform or function are always to be carried out.

Individual agreements are possible and are to be documented in the 3-D CADmodel. (The following rule applies to the CAD drawing: All radii are to be describedexactly.)

Representative standard values are for example:for sheet metal body parts: all radii > 3 mmfor major components: all radii > 1 mmfor chamfer: chamfer length > 1 mm

2.6.2 Representative production specific additions

2.6.2.1 Drillings

Problem description: Not only the theoretical but also the virtual resulting ge-ometry can be essential for the description of a drilled hole. The most importantthing here is the comprehensibility of the intended design.

Recommendation: The depiction of a drilled hole in wire and surface models isrecommended as follows:

Centre (breakthrough point of the centre line through the face), axis and circle withnominal diameter, as well as the curve on the face shall be presented. The depthof the bore hole shall be depicted through the centre point and an additional pointon the drilling axis.



2.6.2.2 Holes, indents, stiffening corrugations in sheet metal parts

Problem description: Similar to that for drilling, both the theoretical as well as thevirtual resulting geometry can be essential. Also, here, the comprehensibility of theintended design is most important.

Recommendation: Holes without collars and free pressings (punch) shall be de-scribed with a 3-D outline on the face.In the case of holes with collars, the collar has to be described; by indentations,the indents have to be described.In any case, it must be guaranteed that the untrimmed surface is reproducible.

2.6.2.3 Flange areas, folds/flutes on sheet metal parts

Problem description: Since flange areas and folds/flutes are generally fasteningor contact areas, a symbolic or hinted at depiction is not sufficient.

Recommendation: In a complete surface model, flange areas and folds/fluteshave to be described entirely with faces and explicitly identified.

2.6.2.4 Spot welds by sheet metal parts

Problem description: In the case of the manufacture of sheet metal parts, theintended position of the joining points on the unfinished object plays an importantpart.

Recommendation: Spot welds on sheet metal parts have to be depicted in the3-D CAD model.

2.6.2.5 Methods plans for body work sheet metal parts

Problem description: Methods plans for the manufacture of body work sheetmetal parts describe, besides the geometry (intermediate forms that are createdduring processing), also necessary parameters such as, for example, work align-ments.

Recommendation: By methods plans, the depiction of the work alignment shallbe carried out as lines and the instructions on swivel points as coordinate systems.Both shall be appropriately marked.



2.6.3 Scope of CAD drawings

During the arrangements for the drawing scope, a distinction should be made be-tween drawings, reduced drawings and info drawings:

Drawing: This term describes the technical drawing in conventional, classicalsense according to DIN 199. The corresponding drawing “represents an object inits intended finished condition”; whereby, “in its depiction and with subsequentdetails, it takes into account in a certain manner particular view points of the pro-duction”. To summarise, this means that for us, the fabrication of a product basedon such component part drawings is possible.

In addition to this, an assembly drawing shows functional connections and, to acertain extent, the spatial relationship of several component parts to one an-other.This type of drawing must satisfy the quality criteria agreed upon.

Reduced drawing: The contents (scope) of supplementary CAD drawing datamay be reduced appropriately under the prerequisite that a complete description ofthe component part through a 3-D CAD data model is ensured. This reduced CADdrawing data together with the associated 3-D CAD data model represents the li-able CAD data model. In this connection, it must be guaranteed that by means ofboth these descriptive forms it is possible to produce the relevant component part.Both these types of descriptive forms must satisfy the quality criteria agreed upon.

Information drawing: Information drawings are incomplete, in certain cases, non-scaled depictions of products or component parts. They serve only the purpose ofsupplying information and generally does not fall under any release procedures, orany change services and must not undergo any quality checks. In consideration ofdata quality, the drawing used to make an offer is, for example, also considered tobe an information drawing.

An individual working group in the VDA task group CAD/CAM are involved at thepresent time with establishing concretely and in detail the reduction of drawings.



3 Data checks

This chapter describes checkable quality criteria, which the working group believecan be performed through a program, for developers of check programs and repairprocesses.

3.1 General

A comparison of the data check with other disciplines and the extent of influenceof the data quality was undertaken in the introduction to Chapter 2.

Accordingly, external check programs are required without delay (and quiteprobably not only transitionally) for the control of the generated CAD data. Thedata check takes place through the designer (as “obligation to be performed at ha-bitual place of work” [jur.]) and should be carried out as early as possible andregularly. A “Batch version” of the check program makes the integration in anautomated process possible (i.e. archiving, data exchange, etc.). The “accep-tance” of the various check programs through the responsible working group forthis recommendation shall assure, among other things, the correctness of the re-sults of the check program and the uniformity of the control protocol.

The automated correction of quality deficiencies (“Healing”) is controversial.Healing is not always possible and can lead to unintentional changes in the ge-ometry. The correct generation is, therefore, in all cases to be given preference.Nevertheless, Healing can be an enormous help by the correction of incorrectmodel depictions. The working group has therefore expressed their approval forthe use of healing in individual cases under the following check criteria.

If healing is to be employed, then its employment at the point where the data wasgenerated/sent should always be favoured over that of the (automatic) healing onthe recipient side.

Chapter 3: Data check


3.2 Fundamental conditions

• The following listed implementation suggestions, i.e. implementation within theframework of a check program or for the automatic correction (Healing), are tobe taken literally as being just that, only suggestions. They represent a possi-ble solution, without any claim to priority by the implementation.

• The check program shall be taken as being only a rough check of the CADmodel. The execution of a finer check is the task of special programs.

• A reference concerning interactive correction of quality deficiencies is logicaland desirable, but not obligatory.

• An optional automatic correction (“Healing”) of quality deficiencies shall beconfigurated through the user, the same as for every other change of the startmodel (e.g. addition of element names, check results, protocol file name, etc.),to be selectable, comprehensible and when possible reversible (“UNDO”).

• Healing possibilities are no obligation disciplines of the check program, but ifon hand will be “carried out”.

• The check programs should be able to run on the supporting hardware plat-forms of the respective CAD system and the relevant current operating systemversions. Where necessary, by versions/release changes of the “basic soft-ware” the check programs must be promptly made/kept runnable.

• The check program must not only be capable of running interactively but alsoas a background process. One should refrain from the use of the “UNDO” pos-sibility “in Batch”.

• The check program shall be structured in modules and the part checks must becapable of being carried out by the user individually or in any combination.

• Limiting values and other basic values of the part checks should be suggestedvia a configuration file, must be capable however of being changed in the dia-logue.

• A selection/limitation of the check scope (with regards to the elements of themodel) must be possible, but at the same time also be capable of checking ab-solutely all elements.

• The writing of the protocol of the check run, inclusive information concerningfaulty elements, takes place in a protocol record (see also Chapter 3.5).The relationship between the protocol record and the CAD model must be rec-ognisable (i.e. the protocol record name must be included in the CAD modeland/or the CAD model name must be included in the protocol record).

• The affected, faulty elements must be explicitly identifiable.



3.3 Mathematical geometry check

Summary of the criteria which is capable of being checked per program(incl. details regarding the version of the stipulation, VDA 4955 V1 or V2; “+”: was expanded

Definition inChapter

Criterion Checkchapter

Abbreviationin Table 4.2

Version

2.3.1 for Curves 3.3.12.3.1.1 Tiny elements, Tiny segments 3.3.1.1 M1 V12.3.1.2 (approximation) identical elements 3.3.1.2 M2 V1+2.3.1.3 Continuity 3.3.1.3 M3a, M3b, M3c V12.3.1.4 Polynomial degree 3.3.1.4 M4 V12.3.1.5 Waviness in planar curves 3.3.1.5 M5 V12.3.1.6 Self penetration 3.3.1.6 C7 V22.3.1.7 Multiple knots 3.3.1.7 M6 V22.3.2 for Surfaces 3.3.22.3.2.1 Tiny elements, Tiny segments 3.3.2.1 M1 V12.3.2.2 Tiny Segment edge 3.3.2.2 SU8 V1+2.3.2.3 (approximation) identical elements 3.3.2.3 M2 V12.3.2.4 Continuity 3.3.2.4 M3a, M3b, M3c V12.3.2.5 Polynomial degree 3.3.2.5 M4 V12.3.2.6 Waviness 3.3.2.6 M5 V12.3.2.7 Min. curvature radius 3.3.2.7 SU9 V12.3.2.8 Angle between edge curves of surfaces 3.3.2.8 SU10 V22.3.2.9 Reversal of normals 3.3.2.9 SU11 V22.3.2.10 Patch amount / distribution 3.3.2.10 SU12 V12.3.2.11 Unoccupied patch rows 3.3.2.11 SU13 V12.3.2.12 Multiple knots 3.3.2.12 M6 V22.3.3 for bounded surfaces (Faces) 3.3.32.3.3.1 Tiny element 3.3.3.1 M1 V12.3.3.2 Tiny edge curve 3.3.3.2 M1 V22.3.3.3 Continuity of boundary curves 3.3.3.3 M3a V22.3.3.4 Penetration/contact of boundary curves 3.3.3.4 F14 V12.3.3.5 Proximity of boundary curve to surface 3.3.3.5 F15 V22.3.3.6 Parallel path within a boundary curve 3.3.3.6 F16 V22.3.3.7 (ass.) No. of segm. in a boundary curve 3.3.3.7 F17 V22.3.4 for Topologies 3.3.42.3.4.1 Continuity 3.3.4.1 M3a, M3b, M3c V12.3.4.2 Junctions 3.3.4.2 T18 V22.3.4.3 Alignment/orientation of similar normals 3.3.4.3 T19 V12.3.4.4 Knife edge 3.3.4.4 T20 V22.3.5 for Solids 3.3.52.3.5.1 General criterion for BRep (2.3.2 to 2.3.4) 3.3.5.1 M1-T20 w/out C7 V22.3.5.2 Tiny element 3.3.5.2 M1 V22.3.5.3 Distance to Vertex-Edge 3.3.5.3 SO21 V22.3.5.4 Distance to Vertex-Face 3.3.5.4 SO22 V22.4.4.3.4 No bypassing of History 3.3.5.5 SO23 V22.4.4.3.5 Superfluous (auxiliary ) geometry 3.3.5.6 SO24 V22.4.4.3.6 (unintentional) cavities 3.3.5.7 SO25 V22.4.4.3.9 Multi-Body-Solids 3.3.5.8 SO26 V22.4.4.3.10 Multi-Solid-Parts 3.3.5.9 SO27 V22.3.6 for Drawings 3.3.62.3.6.1 Tiny elements, tiny segments 3.3.6.1 M1 V12.3.6.2 (approximation) identical elements 3.3.6.2 M2 V1+2.3.6.3 IGES conform texts 3.3.6.3 D28 V12.3.6.4 Polynomial degree 3.3.6.4 M4 V1



3.3.1 Criteria for wire geometry

3.3.1.1 Tiny elements, Tiny segments

Problem definition: Elements, whose extent is smaller than a stipulated accuracywill be marked.

Check scope: All curves according to the list in attachment 2.

Implementation suggestion: Expansion of the elements/segments via the dis-crete length (line = length, circle = circumference, etc.) or approximate: Distributeequally 10 points along the visible part of the element/segment taking into consid-eration the parameterisation and then the chord length may be calculated from theresulting traverse paths. Should this chord length be smaller than the stipulatedaccuracy, then the element will be marked.

Healing: Optionally the marked tiny element may be deleted, as long as it is notrequired for the development of higher ranking geometry. In this case a noticeshould be given out.


Problem definition: Determination by approximation all identical wire and contourgeometry of similar and different element types as well as different extents.

Check scope: Curves according to the list in attachment 2, with the exception ofUV-curves and face curves.

Implementation suggestion: Geometrical comparison of the co-ordinates of 5points equally distributed along the smallest curve length, including the startingand end points. In practice, this approximate examination has proved to be satis-factory.

Healing: Optionally, all identical elements can be deleted except for a small rest (ifappropriate, the largest), as long as they are not required for the development ofhigher ranking geometry or are in possession of references to other elements.Analytically described elements should be given preference for retention.

3.3.1.3 Continuity

Problem definition: To be checked are the continuity in location/position, gradientand curvature of individual curves in relationship to their segments, or per appro-priate elements of combined curve paths. The continuity of non-combined curvepaths cannot be checked due to missing data concerning the relationship toneighbouring geometry.



Check scope: Curves according to the list in attachment 2, with the exception ofanalytical wire geometry and surface curves (will be carried out separately).

Implementation suggestion: Position continuity: End or Starting points of neigh-bouring curve segments, or topological neighbouring curves will be checked forsufficient distance with the aid of a 3-D “intercept tolerance” TOL1, starting fromone of the points. Where these exceed the tolerance they will be marked.

Tangential continuity: Under the prerequisite that position continuity is given, thetangential angle in the adjacent end point of the segment or curve may be deter-mined. Should its difference lay above an angle tolerance TOL2, the affected ele-ments will be marked.

Curvature continuity: Under the prerequisite that point and tangential continuity isgiven, the curvature radii in both will be determined. If the relative difference of theradii lies above a curvature tolerance TOL3, the affected elements will be marked.

Healing: The working group has no recommendation for automatic correction.


Problem definition: A check shall be made to determine whether the polynomialdegree of a curve exceeds the pre-set upper limit.

Check scope: Curves according to the list in attachment 2, with the exception ofanalytical wire geometry and UV-curves

Implementation suggestion: Determine the polynomial degree on the basis ofthe mathematical description and compare with the pre-set limits. Elements withhigher polynomial degrees will be marked.

Healing: Approximation within the bounds of the accuracy for identical elements.This can possibly cause an increase in the number of elements/segments.

3.3.1.5 Waviness in planar curves

Problem definition: The waviness of a planar curve shall be checked through thenumber of sign changes along the curvature over its visible range.

Check scope: Curves according to the list in attachment 2, with the exception ofanalytical wire geometry.



Implementation suggestion: The simplest way of acquiring the number of signchanges is through approximation, in that the curvature shall be calculated from arow of curve points (e.g. dependent upon a polynomial degree of 3-9 per seg-ment). One can rate a curve as being wavy if, for example, the number of signchanges within a segment is >1 or within a triple segment >2.

In order to avoid marking an almost linear curve with only minimal curvature diffe r-ences as being wavy, the change of signs of the curvature should only then betaken into account if the sum of the curvature on both sides of the change of signsis larger than a variable lower limit, e.g. 1/1m .


3.3.1.6 Self intersection

Problem definition: Intersection of two different curve segments and self inter-section of one segment shall be found.

Check scope: Curves according to the list in attachment 2, with the exception offace curves (takes place by implication through naturally bounded surfaces orseparately as a boundary curve of a face).

Implementation suggestion: Attempt to exclude self intersection with the aid ofdisjunctive envelope boxes. Should the envelope boxes intersect one another, oneshould try envelope boxes around smaller sections and cautiously work ones waytowards possible intersections through the bipartitioning process, or totally excludethem.



Problem definition: The knot vectors of NURBS curves should be examined tosee whether two knots within a variable tolerance can be considered as beingidentical. The curve should be marked.

Check scope: NURBS curves.

Implementation suggestion: Read-out knot vectors and then compare knot va l-ues.




3.3.2 Criterion for surfaces

3.3.2.1 Tiny elements / Tiny segments

Problem definition: Face and Face patches whose extent in at least two oppos-ing directions are smaller than the stipulated tolerance, will be marked (“Patchstrips”). Likewise, patch strips whose “smaller” extent in proportion to a neigh-bouring patch is less than 1:100 (“Patch strips”) shall be marked.

Check scope: Faces according to the list in attachment 2, with the exception ofplanar surfaces.

Implementation suggestion: Taking into consideration the parameterisation, 10points will be distributed equally on each of the four boundary or segment curvesand the chord length then calculated from the resulting traverse paths. Should allfour chord lengths or two opposing chord lengths be smaller than the stipulatedtolerance or smaller than 1%, in regard to a neighbouring segment, the elementwill be marked.

Healing: Make elements superfluous by combining with neighbouring elementsand/or delete.

3.3.2.2 Tiny segment boundary

Problem definition: Faces and Face patches whose extent is smaller in one pa-rameter direction than a stipulated tolerance will be marked.

Check scope: Faces according to the list in attachment 2, with the exception ofplanar surfaces.

Implementation suggestion: Taking into consideration the parameterisation, 10points will be distributed equally on every boundary or segment curves and thechord length then calculated from the resulting traverse paths. Should exactly onechord length be smaller than the stipulated tolerance, the element will be marked.



Problem definition: Determination by approximation all identical, naturallybounded surfaces of similar and different element types as well as different ex-tents.

Check scope: Faces according to the list in attachment 2.



Implementation suggestion: Geometrical comparison of a dot matrix of sufficienthigh number including the corner points of the (smaller) face with the others. Thisimplementation suggestion is not sufficient in every case; however, from practicalexperience, almost always enough.

Healing: Optionally, all identical elements can be deleted except for a small rest (ifappropriate, the largest), as long as they are not required for the development ofhigher ranking geometry or in possession of references to other elements. Analyti-cally described elements should be given preference for retention. The visibilitystatus of the remaining elements shall be examined and corrected where neces-sary.

3.3.2.4 Continuity

Problem definition: To be checked are the continuity in location/position, gradientand curvature of individual, naturally bounded surfaces in relationship to theirsegments. Elements as well as location of the discontinuity shall be marked.

Check scope: Faces according to the list in attachment 2, with the exception ofanalytical faces and face cut-outs/sections.

Implementation suggestion: Position continuity: The parity of two neighbouringsegment boundaries will be checked at a variable number of points. Should themaximum gap lay above a gap tolerance TOL1, the affected patch boundariesshall be marked and the maximum gap depicted.

Tangential continuity: Under the prerequisite that position continuity is given, thetangential angle of two segments along the common border will be determined ona variable number of points and a calculation of their difference. Should the maxi-mum difference in the angle lay above an angle tolerance TOL2, the affectedsegment boundary shall be marked and the maximum kink/flaw depicted.

Curvature continuity: Under the prerequisite that position and tangential continuityis given, the curvature radii of two segments along the common border will bechecked at a variable number of points. Should the maximum relative curvaturedifference lay above a curvature tolerance TOL3, the affected segment boundaryshall be marked and the maximum curvature difference depicted.



Problem definition: A check shall be made to determine whether, in at least oneparameter direction, a polynomial degree of a surface does not exceed the pre-setupper limit.

Check scope: Faces according to the list in attachment 2, with the exception ofanalytical faces and face cut-outs.



Implementation suggestion: Determine the polynomial degree on hand from themathematical description and compare with the pre-set limiting value. Elementswith a higher polynomial degree will be marked.

Healing: Approximations within the bounds of tolerances for identical elements.This can possibly cause an increase in the number of elements/segments.

3.3.2.6 Waviness

Problem definition: The waviness of a naturally bounded surface shall bechecked through the number of sign changes along the length of the Isoparameterlines u = u1...u = un und v = v1...v = vm.


Implementation suggestion: It is easiest to determine the number of signchanges along the length of an isoparameter line, in that the face curvature is cal-culated on hand from a row of points, where necessary, dependent upon a poly-nomial degree of approx. 3-9 per parametric line. Note: (Face curvature mentionedhere means - normal curvature of the face in the direction of the curve). A facewith more than three changes of sign along the total length of a parametric line ormore than one within one of its segments would be rated as being wavy.

In order to avoid marking an almost planar face with only minimal curvature differ-ences as being wavy, the change of signs of the curvature should only then betaken into account if the sum of the curvature on both sides of the change of signsis larger than a variable lower limit, e.g. 1/1m .


3.3.2.7 Minimum curvature radius

Problem definition: Ranges of naturally bounded surfaces in which the curvatureradius is less than a given value shall be found and marked. Places, in which thenormal to a face is not defined and where also no curvature radius can be deter-mined, should especially be marked.


Implementation suggestion: Determine the maximum positive and negative cur-vatures on hand from a variable number of face points (e.g. n times m intersec-tions of isoparameters) and compare every time with the limiting value.




3.3.2.8 Angle between the boundary curve of surfaces

Problem definition: A check shall be made to see whether the angle between theboundary curves of naturally bounded surfaces lie within the critical range around0° or 180°.

Check scope: Faces according to the list in attachment 2, with the exception offace cut-outs/sections.

Implementation suggestion: Determine the angles between the tangents of theneighbouring boundary curves and compare with the specified tolerance TOL.Mark transitions of smaller TOL° or larger 180-TOL°.


3.3.2.9 Reversal/inversion of normals

Problem definition: Ranges of naturally bounded surfaces in which a big localchange in the difference of the normal angle has been ascertained, shall be ex-amined and marked.

Check scope: Faces according to the list in attachment 2, with the exception offace cut-outs.

Implementation suggestion: Generate the 4 corner normals of the face segmentand a normal in each of the parametric centre points of the four edges as well asin the centre of the face and make a comparison within each group. Thereby, thelargest angle difference may not exceed a specified value (e.g. 170°). So thatfaces with constant changes in the normals (e.g. cylinder jacket face) will not bemarked the specified value may be changed to 120°.


3.3.2.10 Patch amount / distribution

Problem definition: Determine surfaces with a high number of patches and markaccordingly.


Implementation suggestion: Determine the number of patches on each surfaceand compare with the stipulated value.




3.3.2.11 Unoccupied patch rows

Problem definition: Determine surfaces with unoccupied patch rows and markaccordingly.

Check scope: Faces according to the list in attachment 2, with the exception offace cut-outs/sections.

Implementation suggestion: For every outside boundary curve of a boundedsurface, the patch rows of the surface upon which the boundary curve lies will bemarked. If, after this test, there are patch rows in u or v direction which have notbeen marked, then the surface will be marked as being incorrect/faulty.

Healing: Optional removal of the unoccupied patch rows, i.e. reduction of the sizeof the surface.


Problem definition: The knot vectors of a B-Spline or NURBS face in u and v di-rection should be examined to see whether two knots within a variable tolerancemust be considered as being identical. The face should be marked.

Check scope: B-Spline and NURBS faces.

Implementation suggestion: read out knot vectors and compare the knot valueswith the tolerance.




3.3.3 Criterion for bounded surfaces


Problem definition: Bounded surfaces, which fall short of a particular size will bemarked.

Check scope: Trimmed faces according to the list in attachment 2.

Implementation suggestion: Calculate the face contents of the bounded surfaceand compare with a pre-set minimum value.

Healing: Delete element and adapt (topological) neighbouring elements

3.3.3.2 Tiny curves

Problem definition: Boundary curves, whose extent is smaller than a pre-set tol-erance will be marked

Check scope: Boundary according to the list in attachment 2.

Implementation suggestion: Calculate the curve length of the boundary curveand compare with a pre-set minimum value.

Healing: Delete the elements and trim the neighbouring boundary curves, or com-bine/consolidate with a neighbouring curve.

3.3.3.3 Continuity of boundary curves

Problem definition: The boundary curves of bounded surfaces shall be checkedfor gaps or overlapping of their segments respectively, as well as among eachother.

Check scope: Trimmed faces or respectively, their boundaries according to thelist in attachment 2.

Implementation suggestion: End or Starting points of neighbouring curve seg-ments will be checked for their proximity to one another with the aid of the toler-ance TOL1, starting from one of the points. The point where the tolerance is ex-ceeded will be marked.




3.3.3.4 Intersection or contact of boundary curves

Problem definition: All bounded surfaces in the model will be checked whether,within a set tolerance, the face curve paths that form the boundary intersect them-selves or whether face curve paths of a bounded surface interpenetrate or havecontact with one another.


Implementation suggestion: Boundary curves (face curve paths that form aboundary) are on hand in the parametric space of the surface (UV-curve, 2-Dcurve) and/or in 3-D space (3-D curve). The most suitable medium for checkingthe intersection or contact of the boundary curve with itself or with other boundarycurves of the same surface is the UV-curve. For the check, the curve will be parti-tioned into sufficient distinct polygon segments so that the exactness of thesepolygons lay somewhat under the pre-set control tolerance. Should segments thatare not neighbours come nearer to one another than the check tolerance, then acontact or an intersection respectively, has occurred. This process will also be car-ried out for boundary curves opposed to each other. The projection of the con-tact/intersection points onto the surface will be marked.


3.3.3.5 Proximity of boundary curves to the surface

Problem definition: The boundary curve bounded surfaces shall be checked withregards to the proximity to appurtenant surfaces. A check should also be madewhether the boundary curve extends beyond the parameter range of the surface.

Check scope: All edges that form the boundary of a bounded surface and the ap-purtenant surface. In many CAD systems the bounds of bounded surfaces are de-fined in the parameter range of the surface. For these CAD systems it only makessense to determine the distance to the surface if the boundary curve has a refer-ence to a relevant 3-D curve.

Implementation suggestion: Distribute points along a boundary curve at ameaningful distance from one another and then project them onto the surface.Should the distance of a point to the projected point be larger than the stipulatedtolerance, the boundary curve will be marked. If, over and above that, a projectedpoint extends beyond the parameter range of the surface, the distance to theboundary curve of the surface will be determined and the boundary curve marked.

Healing: Optional projection, as long as the surface must not be extrapolated.



3.3.3.6 Rectified/Equiaxial rotation within a boundary curve

Problem definition: Connected boundary curves shall be checked for their recti-fied/equiaxial sense of rotation. Elements with a sense of rotation working in theopposite direction (minority) shall be marked.


Implementation suggestion: For every enclosed curve path of the boundary, acheck will be made to see whether, for every individual curve end point, the startpoint of the following curve lies nearer than its end point.

Healing: Generate bounded surfaces anew through new orientated boundarycurve(s).

3.3.3.7 (Reasonable) Segment amount in boundary curves

Problem definition: Identify and mark boundary curves with (adjustable) higheramount of segments.


Implementation suggestion: Determine the number of segments of everyboundary curve and compare with the specified value.




3.3.4 Criterion for surface groups, topologies

3.3.4.1 Continuity

Problem definition: In order to determine the continuity of a structure createdfrom bounded surfaces, the topological association of these faces must first of allbe determined, where necessary, established, in case this has not been fulfilledthrough topology elements. Details concerning “Topology generators” will not becarried out here. With the help of these specified or generated “nominal relation-ships”, the continuity of the topology will then be checked with regard to loca-tion/position, gradient and curvature. Elements as well as the location of disconti-nuity shall be marked.

Check scope: Open and enclosed/endless groups according to the list in attach-ment 2.

Implementation suggestion:

The continuity will be checked based upon the common face edges:

Position continuity: The parity of two common boundary curves will be checkedagainst a variable number of points. Should a discovered gap lay above a gap tol-erance TOL1, the affected face boundary will be marked.

Tangential continuity: After passing the position continuity check, the tangency an-gle or normal angles of two faces in the common boundary curve will be checkedat a variable number of points. Should an angle difference that is consequentlydiscovered lay above an angle tolerance TOL2, the affected boundary curve willbe marked.

Curvature continuity: After passing the point and tangential continuity checks, thecurvature radii of two faces in the common boundary curve will be checked at avariable number of points. Should a relative curvature difference that is conse-quently discovered lay above a curvature tolerance TOL3, the affected boundarycurve will be marked.


3.3.4.2 Junctions

Problem definition: The topological consistence, i.e. explicitness and the unity ofsurface groups, as well as the absence of junctions shall be checked. The locationof multiple junctions shall be marked.

Check scope: Unified groups according to the list in attachment 2.



Implementation suggestion: Find the junctions via a comparison of the boundarycurves of the individual faces. A boundary curve may have per section a maximumof one other boundary curve that is completely or only partially congruent.

Healing: Remove the “superfluous” face from the closed surface group, so long asit can be explicitly identified.

3.3.4.3 Orientation of similar normals

Problem definition: Every face of the group shall be checked as to whether theneighbouring faces have the same orientation of the normals. By contra orienta-tion, the faces of least amount (minority) shall be marked. Should the definition ofthe topology element allow the pre-setting of a particular direction/orientation, thena check will be made to see whether all the normals comply with this orientation.

Check scope: All trimmed faces of open and enclosed (unified) groups accordingto the list in attachment 2.

Implementation suggestion: For all neighbouring face pairs, the middle point onthe common curve shall be examined. Normals directed in the opposite direction(minority) and normals that are contrary to that stipulated will be marked.

Healing: In the case of closed/unified groups, align all normals to the outside(“away from the material”) or to the inside (“towards the material”), it is optionalunder open groups whether the minority is reversed or not.

3.3.4.4 Knife edge

Problem definition: The faces of a composite surface whose angle between thetangential planes on a common boundary curve (or parts thereof) show propertiesof a minute angle of nearly 0 degrees shall be marked .

Check scope: Surface groups/ composite surfaces according to the list in attach-ment 2.

Implementation suggestion: Independent of the face types and curvature, cal-culate the angle between the tangential planes at a number of restartpoints/fulcrums. Mark all angles found that are around 0 degrees

Healing: The working group has no recommendation for automatic correction



3.3.5 Criteria for solids

3.3.5.1 Utilisation of the check criteria 3.3 .2 to 3.3.4 on solids

Problem definition: The whole of all bounded surfaces of the solid forms a sur-face group. This shall be examined in accordance to the criteria laid out in 3.3.4.Every individual face of the surface group is to be checked in accordance to thecriteria in 3.3.3. The individual faces in turn are the basis/foundation of the surface.These are to be checked in accordance to the criteria laid out in 3.3.2.

Check scope, Implementation suggestion: see under 3.3.2 to 3.3.4.


3.3.5.2 Tiny elements by Solids

Problem definition: Solids, whose expansion in two spatial directions is smallerthan a stipulated tolerance will be marked.

Check scope: Solids according to the list in attachment 2.

Implementation suggestion: The enveloping rectangular solid will be calculatedfrom the maximum expansion in the three main directions of the solid (e.g. mainaxis of inertia). Should the extension of the rectangular solid be smaller in two co-ordinate directions than the defined tolerance, the element will be marked. In addi-tion, the volume of the solid will be calculated and ascertained whether it falls shortof a stipulated minimum value for the volume.

Healing: Optionally, the marked tiny elements may be deleted, as long as they arenot associatively connected with other geometry. In this case a notice should begiven out. The capability for regeneration of the changed solid must be guaran-teed!

3.3.5.3 Distance Vertex - Edge

Problem definition: If the distance between Vertex and Edge exceeds a specifiedtolerance value then Vertex and Edge shall be marked.


Implementation suggestion: Geometrical proximity calculation.

Healing: Projection of the Vertex onto the correct corner point.



3.3.5.4 Distance Vertex - Face

Problem definition: If the distance between Vertex und Face exceeds a specifiedtolerance value then Vertex and Face shall be marked.


Implementation suggestion: Proximity calculation.

Healing: Projection of the Vertex onto the Face.

3.3.5.5 No bypassing of the history

Problem definition: It should be ascertained whether solid components in theform of B-Reps (Boundary representations) were imported into the existing modeland, if appropriate, mark them.

Check scope: Solids according to attachment 2.

Implementation suggestion: Utilisation of the CAD internal analysis tools.

Healing: The working group has no recommendation for automatic correction

3.3.5.6 Superfluous (auxiliary) geometry

Problem definition: Solid elements that are no longer on hand (e.g. cut-off com-ponent part areas, “dead branches”) are to be identified and marked.Identify and mark material additions in component part areas, which are alreadyfilled with material (e.g. addition of a ball/sphere fully in a rectangular solid), with-out the component part changing in any way.Identify and mark geometrical elements which have no logical relationship to solidsthat are on hand.

Check scope: Closed/Unified groups and solids according to attachment 2.


Healing: Optional deletion of all elements which are included in another elementand elements that are not related to the solid. The capability for regeneration ofthe changed solid must be guaranteed!

3.3.5.7 (Unintentional) Cavities

Problem definition: Solids which are fully contained in another one and which areto be subtracted from it, shall be identified and marked.

Check scope: Closed/Unified groups and solids according to attachment 2.




Healing: The marked cavities can be optionally deleted.

3.3.5.8 Multi-Body-Solids

Problem definition: Solids from the addition of disjointed components shall beidentified and marked.



Healing: Optional, undo and create individual solids.

3.3.5.9 Multi-Solid-Parts

Problem definition: A determination shall be made as to whether several solidsare on hand in the existing model and, where necessary, to mark them.



Healing: Optional, divide into several CAD models of the same name with con-tinuous numbering index (e.g. flange will become Flange_1, Flange_2, etc.).

3.3.6 Criterion for drawings


Problem definition: Identify and mark drawing elements which are less than aparticular dimension.

Check scope: Curves of the drawing range according to the list in attachment 2.

Implementation suggestion, Healing: see 3.3.1.1.


Problem definition: Equalise approximated identical drawing elements and iden-tify and mark different element types.

Check scope: Curves of the drawing range according to the list in attachment 2.

Implementation suggestion, Healing: see 3.3.1.2.



3.3.6.3 IGES conformal texts

Problem definition: Find and mark texts with non IGES conformal fonts.

Check scope: Texts (not dimensions)of the drawing part.

Implementation suggestion: Examine texts for fonts unlike ISO fonts 1001-1003.

Healing: Optionally replace texts. The space requirement due to the transforma-tion (e.g. vowel mutation ä in ae) can become larger. Because of this the format-ting can get lost.

3.3.6.4 Polynomial degrees of drawing elements

Problem definition: A check shall be made as to whether the polynomial degreeof a curve exceeds the pre-set upper limit.

Check scope: Spline and offset curves of the drawing range according to the listin attachment 2.

Implementation suggestion: Determination of the polynomial degrees on handfrom the mathematical description and compare this with the pre-set limits. Ele-ments with high polynomial degrees will be marked.

Healing: Approximation within the bounds of the tolerance for identical elements.This can possibly cause an increase in the amount of elements/segments.

3.4 Organisational check of the model

The definition and checking of organisational quality criteria (e.g. the assignmentof layers, designation conventions, etc.) will be described in the next version of thisVDA Recommendation. Until that time, the organisational model check will be re-stricted to a model statistic in the control protocol.



3.5 Structure of the protocol record file

The protocol record file shall be easily understandable for the user and wherepossible, uniform for all CAD systems or check programs respectively. The proto-col record is divided into three essential sections (see chapters 3.5.1 till 3.5.3).

The protocol record shall be capable of being evaluated through the program. Forthis reason, the edition takes place in form from keywords in connection with de-scriptive texts. This can be arbitrarily long and will be concluded through the nextkeyword. The keyword is constituted from a free configurable but fixed characterchain (here: **) which is placed in front of the actual keyword. The descriptive textcan be structured through free configurable information separators (, or ;).

The line length of the protocol record file shall be limited to 80 characters.

A short description of the changes made in comparison with the specifications forthe VDA4955 version 1 can be found in the chapter 3.5.4.

3.5.1 Model structure

The checked model shall be described in this first section of the protocol record fileand general information concerning the contents of the model issued.

**Keyword Description

**BEGIN_MODELSTRUCTURE**KNOT Source computer**DIRECTORY Source directory**MODEL Name of the checked model**CHANGE last storage/change date**USER User of the last change**CAD-SYSTEM Source system incl. version**OP-SYSTEM Operating system incl. version**BYTE Size of the model in Bytes**COMMENT Contents of the internal model description (ifavailable)**STANDARDS Listing of the internal model graphics and ex-actitude

standards, etc.**TYP List of the utilised element types incl. theirnumber**COLOR List of the utilised colours incl. number of ele-ments**STRUCTURE List of the utilised structure elements (i.e. Layer,Set, etc.

incl. number and/or name) including the number of theelements lying in / on them

**END_ MODELSTRUCTURE



3.5.2 Summary of the control run and check results

In this second section a rough summary in table format concerning the check willbe given. This table must be capable of being optionally stored in the CAD model.

The columns "Par.1" to "Par.3" depict the set limits, column "sel. Ent" contains thenumber of checked elements, "vio. Ent" cites the number of defective elements.

The list of the criteria must always be completely entered.

- with "sel. Ent" means: criterion switched off,0 with "sel. Ent" means: no element selected/found,0 with "vio. Ent" means: no defective elements found.

25 characters !4 CH !9 CHAR. !9 CHAR. !9 CHAR. !9 CHAR. !9 CHAR.=80

**BEGIN_OVERVIEW_CHECKRESULTCriteria !Short! Par.1 ! Par.2 ! Par.3 ! sel. Ent ! vio. EntTiny elements !M1 ! ! ! ! !ident. elements !M2 ! ! ! ! !G0-Continuity !M3a ! ! ! ! !G1-Continuity !M3b ! ! ! ! !G2-Continuity !M3c ! ! ! ! !...etc. to...IGES conform. texts !D28 ! ! ! ! !**END_OVERVIEW_CHECKRESULT



3.5.3 Detailed test results / visualisation

The implementation of the check results (e.g. with regards to the degree of detail-ing, structure, details about element designations, etc.) is left up to the individual,since it is very much dependent on the system and usually, dependent upon theprogram for the visualisation of the check results. The detailed check result shouldbe framed within the protocol data record file, with the following keywords:**BEGIN_DETAILS_CHECKRESULT**END_DETAILS_CHECKRESULT

A visualisation of the defective elements including the location of the error must bepossible. Thereby, the capability should be offered to zoom onto the defectiveelement or the location of the error.

An additional text description of the errors should be capable of being displayedduring the visualisation.

The possible conversion of temporary elements for the depiction of the errors (e.g.points, vectors by angles, etc.) in permanent elements is occasionally very helpful,but is not obligatory.

Possible recommendations for interactive correction or healing possibilities withthe appropriate "UNDO" possibilities should be offered in association with thevisualisation of individual errors.

3.5.4 Changes compared to VDA4955 version 1

- STRUKTUR changed to STRUCTURE.

- Keyword LINETYPE from **MODELSTRUCTURE was deleted

- The section "Violate Entity" and "Criterions" were deleted, since both werejudged to be more confusing than helpful during the application of the checkprogram V1

- Description/Definition of the visualisation was added (in 3.5.3).



4 User aids

The following listed user aids provide an incomplete and “living” collection ofproven procedures that have been given approval by the working group.

4.1 Further sources of information(without claim to completeness or relevance to the current situation; random sequence)

4.1.1 www.odette.org (ODETTE Homepage)

4.1.2 www.vda.de (VDA Homepage)www.vda.de/public/schrift4.htm (direct to the recommendation,

at the present time not yet Dialog-/Download capable)

4.1.3 www.prostep.de/BP (ProSTEP GmbH, "Best Practices" for STEP utilisation, etc.)

4.1.4 www.ceg.org ("CATIA implementation group", IG CATIA user FZG manufacturer)

4.1.5 www.zulieferer.bmw.de (BMW-CAD-Homepage)

4.1.6 www.tandem.mercedes-benz.com (DaimlerChrysler-CAD-Homepage)

4.1.7 www.vw-zulieferer.de (VW-CAD-Homepage)

4.1.8 extranet.audi.de (AUDI-CAD-Homepage)

Chapter 4: User aids


4.2 Limit recommendations for check program of version 1(for two essential component categories in the manufacture of vehicles)

Criteria(possibly applicable for severalgeometry types)

Alwayscheck!

Class A Class B

1 Polynomial degree 11 11

2 minimum curvature radius, flip over

X 0,5 mm 0,5 mm

3 Waviness of planar curves not allowed not allowed

4 Waviness of faces not allowed not allowed

5a Continuity G0 (position) X 0,01 mm 0,02 mm

5b Continuity G1 (gradient) 0,1° 1°

5c Continuity G2 (curvature) - -

6 Synonymous orientation of normals

X Must be Must be

7 Absolute / relative patch size 0,02 / 1/100 0,02 / 1/100

8 max. amount of patches 200 200

9 Identical elements X 0,001 mm 0,02 mm

10 Tiny elements X 0,02 mm 0,02 mm

11 Face boundary curve X 0,01 mm 0,02 mm

12 Unoccupied patch rows not allowed not allowed

13 Non IGES fonts not allowed not allowed

14 Model structure meaningful,retraceable,documented

meaningful,retraceable,documented

• The limits and minimum criteria listed here (always check the columns!) arerecommendations which can be replaced at any time through suitable, bilateralagreements.

• In order not to overtax the check program and the user, the check scope, i.e.the number of criteria to be checked, shall be kept as small as possible.

• The points in time when the check takes place should occur as early as possi-ble in the process chain (draft and offer/tender phase) and should be regularand often. At fundamental stages of the development (forwarding of data, re-lease, archiving, etc.), the agreed upon data quality must be established anddocumented.

• The data quality and its documentation is an “obligation to bebrought/performed” [juristic term] by the creator/sender.



4.3 Limit recommendations for check program of version 2(for two essential component categories in the manufacture of vehicles)

Criteria(possibly applicable for several geometrytypes)

Alwayscheck !

Class A Class B

M1 Tiny element/segment

M2 (approx.) ident. elements

M3a Continuity G0 (position)

M3b Continuity G1 (grade)

M3c Continuity G2 (curvature)

M4 Polynomial degree

M5 Waviness

M6 Multiple knots

C7 Self penetration of curves

SU8 Tiny segment edge

SU9 min. radius, non defined Normals

SU10 Angle between edge curves

SU11 Reversal/inversion of Normals

SU12 Patch amount/distribution

SU13 Unoccupied Patch rows

SU13Angle of the boundary curves.

F14 Penetration or contact of boundarycurves

F15 Distance of boundary curves to Sur-faces

F16 rectified/equiaxial sense of rotation ofboundary curves

F17 Segment amount in boundary curves

T18 Junctions

T19 Equal orientation of Normals

SO21 Distance Vertex-Edge

SO22 Distance Vertex-Face

SO23 Bypassing History

SO24 Superfluous (auxiliary) geometry

SO25 Unintentional/unwanted cavities

SO26 Multi-Body-Solids

SO27 Multi-Solid-Parts

D28 IGES configuration texts
