Lattice3D – White Paper 3.03.05

Keys to Understanding and Comparing 3D File Formats and their

application to 3D Publishing

Authored by Lattice3D Technical Division The 3D Publishing market – in which 3D data is published by 3D-aware applications in a variety of media - is estimated to exceed $500 million in 2005. Through 3D Publishing the large amount of existing Computer Aided Design (CAD) or Digital Content Creation (DCC) 3D model data is repurposed for use in downstream applications. As a result, the industry has seen a rapid move to the release of various 3D formats that extend the use of existing 3D data. With these releases, 3D data can now be used not just for viewing by supply chain members, but also directly used in downstream applications such as 3D customer manuals, 3D online training, 3D assembly instructions, 3D parts lists, 3D design review, 3D technical documents, 3D manufacturing communications, 3D assembly process definition, 3D quality assurance, 3D packaging design, 3D websites and more. Companies now have to decide which 3D format to use or standardize on. This paper is designed to present the differences between formats in a way that makes this decision easier and more straightforward. As of early in 2005, many 3D publishing formats are available: XVL by Lattice3D, JT/Open by UGS, CGR from CATIA, DWF by Autodesk, U3D from the 3D Industry Forum (3DIF), X3D from the Web3D Consortium, a voxel based format by nGrain, and many intermediate formats by translator and viewer companies such as Elysium, TTF, Actify and Quadrispace. All of these formats offer the promise of repurposing 3D data, but they use at least 3 different technologies to achieve that end. These different methodologies dramatically affect the compression, graphical fidelity, accuracy and performance of the 3D data as it is used downstream. The three major concerns are: Compression for speed of communication and manipulation, Graphical Fidelity for viewing accuracy and Geometric Precision for widest application usability of the data files. Compression Rates 3D CAD solid and surface models are often very data-intensive, resulting in files that can be extremely large and way too bulky to be easily emailed or incorporated into other documents (e.g. training manuals). One of the necessary features of successful 3D publishing is to be able to create files containing 3D data that are small enough to be viewed, used, published and emailed even on low-end or typical office level PCs. Ideally, making these data smaller should not result in loss of geometric accuracy or visual fidelity.

With polygon-based 3D formats, the higher the tessellation, the larger the file size. However, should better compression of the data be required, tessellation can be reduced but is balanced by a corresponding loss in fidelity and geometric accuracy. Regardless, compression of polygon-based data can typically be between 85-95% of the original CAD data file. XVL does not suffer from these issues, typically enabling 1/50 to 1/250 (i.e. better than 98%) compression of the data, in NURBs format, with high visual acuity and accuracy.

JT,

CGR,

DWF,

other

polygon

formats.

.

XVLGeometric Precision

Compression

Low (1-1/10)

Approximate

Precise CAD

~100%

Moderate (1/10-1/30)

High (1/50-1/250 i.e. 98%+)

Downstream User

Requirements

JT,

CGR,

DWF,

other

polygon

formats.

.

XVLGeometric Precision

Compression

Low (1-1/10)

Approximate

Precise CAD

~100%

Moderate (1/10-1/30)

High (1/50-1/250 i.e. 98%+)

Downstream User

Requirements

Figure 1 - Comparison of Polygon and XVL file formats

Fidelity of Viewing Why is this important? The fidelity of the 3D model when it is used, viewed, and shared is often of high importance: while a picture can say a thousand words, vague representations of the design often simply do not communicate the intent and the details that are necessary for comprehension. In practical terms to use the data downstream, e.g. for assembly instructions or spare part selection, it’s of course necessary to zoom in at least to the smallest single part level – if the graphical fidelity of that single part is not good enough to confirm that it’s the right part the system is plainly inadequate. Voxel-based 3D formats, which are based on (volumetric element) rendering technology, end up with ‘grainy’ representations of 3D models of even modest complexity.

2

Polygon-based 3D formats provide very adequate viewing fidelity when the tessellation of the polygons is set to a high level. But each time the tessellation is reduced, the fidelity of the 3D view is affected. Furthermore, the tessellation of the data being used and viewed cannot be re-set within the file, but needs to be re-extracted at a different, higher tessellation level by the originating CAD system or intermediate file system. Some polygon based formats (e.g. JT) can hold multiple LODs (each Level of Detail is higher tessellation version of the polygon model) – these files avoid re-extraction from the originating CAD system but obviously sacrifice compression. XVL provides very high fidelity because it is based on a pure mathematical model that follows all curves very exactly thereby enabling good communication of the data at all levels of zoom without any penalty to the model compression. As XVL is a NURBS-based model, tessellation of the view is performed on-the-fly when a Zoom in (or out) function is called. "XVL breaks the mold with a technology shift, rather than rely on representing product graphics in a tessellated form of planar triangles, XVL uses a higher mathematical surface form allowing for impressive data compression. Less data drives faster data transfer and faster data transfer drives expanded use of that data for collaborating design teams and downstream users of product data." Ken Versprille, Ph.D., PLM Research Director, CPD Associates, LLC (CPDA). Geometric Precision 3D models from CAD systems are created using a variety of solids and surfaces including mathematical-based algorithms such as B-Rep and NURBs to create highly precise 3D models of a design. However, many 3D publishing formats deal only with polygons as a way to represent 3D data. Formats that are polygon-based include DWF, JT, CGR, .3D and more. When polygons are used to represent 3D they create an approximation of a mathematically perfect curve (you may be familiar with zooming in and seeing curves or circles represented by a series of short straight edges). Thus the accuracy of the 3D data in a polygon-based format is dependent on the level of tessellation (basically the number of straight edges approximating a curve) selected when the file is extracted. In general the lower the tessellation, the lower the accuracy of the model, and vice versa with high tessellation. On the upside, though, the lower tessellation allows the file size to be smaller and more easily handled, if the reduced accuracy can be tolerated. Higher tessellation means more polygons so a larger file size results i.e. polygon format file size is proportional to the level of tessellation. To generate a file at a higher level of tessellation usually requires returning to the CAD system or intermediate file stage and generating a new and larger (i.e. less compressed) polygon file. In contrast, when using the accurate mathematical model of XVL, polygons can be generated at time of viewing and quickly regenerated at any level of zoom. XVL, by Lattice3D (an XML format), does not rely on polygon-representation of 3D models. Instead XVL ‘re-surfaces’ 3D models with a form of NURBS called a Gregory Patch. Gregory Patches enable XVL to represent the original models with high accuracy (typical 0.1 to .0001 of the model units) and they compress very

3

tightly. Typically this results in XVL being anywhere between 2 and 5 times higher compression than polygon-based 3D formats without loss of geometric accuracy. The voxel-based 3D publishing formats by nGrain, provide very good compression ratios but low geometric precision on any complex 3D model. 3rd parties are OEMing the XVL technology too - XVL has been adopted by Dassault Systems (who already own the CGR and e-drawings formats) to be incorporated into its upcoming 3D-XML format. “This is a Big Deal. 3D XML, based on Lattice Technology's XVL, comes closer than any other open format to the Holy Grail of 3D: Low-volume, high-precision 3D representations.” Dr. Joel Orr, chief visionary, Cyon Research in his commentary at www.cadwire.net about 3DXML by Dassault. XVL has also been adopted by CoCreate, Docware and CatalogCreator. Downstream Applications Choosing the right format has another key component. It is the capabilities of the format that predicate the functional ability and independence of the downstream applications. Viewing is simply not enough. If a user needs single part viewing or selection, then high graphical fidelity of the single part, within the overall assembly, has to be available. Alternatively if the file is used in, say, a QA system or in an assembly clash detection it has to be highly accurate and if the file is viewed over the web in a sales and marketing system it better be as compressed as possible for the best user experience. XVL excels in all these areas. Conclusion Companies that design in 3D have a valuable asset that can readily be re-used to increase productivity downstream where in most companies between 10 and 30 people can or should use that data - the need to repurpose 3D data in the downstream areas of manufacturing has never been so high as now. The general and widespread acceptance of 3D for product design and manufacturing means that companies can reuse their design data assets across the enterprise and beyond to their suppliers and customers to boost productivity without barriers and delays in communication. Choosing the right standard format is a key foundation decision to be able to repurpose 3D data with the highest flexibility and maximum opportunity for success in this mission. As this white paper explains XVL has broad advantages over voxel and polygon based technologies for 3D publishing purposes.

4

©2005 Lattice Technology, Inc. All rights reserved. Lattice3D, XVL, and 3D Everywhere are trademarks of Lattice Technology USA, Inc. All trademarks and registered trademarks are the properties of their respective companies.

5

Table 1 - Polygon and XVL feature comparison

Item

Polygon Format based competitors

XVL/Lattice3D

Who? Which markets are these advantages important to?

Why? In business terms how important are they?

Breadth of CAD/DCC systems supported

Depends on each particular competitor

All CAD formats via partnership with Elysium (specialist conversion co.)

Users need access to any 3D CAD format that the 3D data may be in

Cost reduction through re-use of any 3D data asset downstream

Compression capability:

Polygon format compressed to typically ~90-95%

XVL NURBs/Gregory patch - typically ~3-5 times higher compression

3D publishing

Significant benefit in 3D digital docs and websites for faster download and therefore better user experience

Accuracy

Approximate - polygon model of indeterminate accuracy depending on tessellation level chosen – good for viewing. Higher tessellation = larger file size

User defined accuracy guaranteed to 0.1, 0.01 or 0.001 of model units – good for viewing and measurement within requested accuracy

Anyone who needs a known accuracy e.g. 3D data in Quality Assurance applications Anyone who wants to control the accuracy of the model so as to control what it can be used for

Can’t check quality/tolerance of ‘as built’ versus ‘as designed’ products without high known accuracy It can very advantageous to deliberately ‘dumb-down’ the model so that it is not suitable for manufacturing but is fine for say assembly animation

Combine different source CAD models (e.g.. Pro/E and SW)

Some

Yes

Users with more than one CAD system to design different components

Cost reduction through re-use of all available 3D data assets downstream

Reset-able tessellation on zoom in

No (because it’s a polygon format with preset tessellation already) unless multiple LODs are created (which sacrifices compression)

Yes (because it’s a NURB based model so re-tessellation done on the fly

Anyone who needs to zoom in on the detail and still have great graphics

3D publishing often needs zoomed in detail – when it does, high quality graphics are vital for high Quality publishing

6