Adobe Retreat, November 12, 2013Adobe Retreat, November 12, 2013

Weak Links in the Chain from

Concept to Construction

Carlo H. Séquin

University of California, Berkeley

40 years of making use of CAD40 years of making use of CAD

CCD TV Camera (1973) Soda Hall (1992)

RISC 1 MicroChip (1982) Octa-Gear (2000)

Recent Designs and ModelsRecent Designs and Models

From Concept to ConstructionFrom Concept to Construction

A vague idea in your head

A sketch that can be shown to others

A first version of a geometrical model

A parameterized CAD model

A fine-tuned version

A file for an RP machine

A tangible RP model

Final scale model

The real thing

PART 1

PART 2

Talk OutlineTalk Outline

PART 1: Concept Input

Creating Parameterized CAD Models

User-Guided Inverse 3D Modeling

PART 2: Obtaining Tangible Output

Slicing Imperfect .STL files

Relying on the Winding Number

PART 1PART 1

How to get started ?How to get started ?

How to get your ideas How to get your ideas into the CAD system?into the CAD system?

Most design activities do not start from scratch!

•A predecessor model needs improvement

•An inspirational artifact stimulates a new design

““Hyperbolic HexagonHyperbolic Hexagon”” by B. Collins by B. Collins

7 tunnels in a disk

4 boundary curves

approx. minimal surface

Aims:

Increase complexity

Maximize aesthetics-- from all directions!

Closing the LoopClosing the Loop

straight

or

twisted

“Scherk Tower” “Scherk-Collins Toroids”

Sculpture Generator ISculpture Generator I, GUI , GUI

Shapes from Shapes from Sculpture Generator ISculpture Generator I

The Finished The Finished HeptoroidHeptoroid

at Fermi Lab Art Gallery (1998).

Brent CollinsBrent Collins’’ ““Pax MundiPax Mundi””

1997: wood, 301997: wood, 30””diam.diam.

2006: Commission from H&R Block, Kansas Cityto make a 70”diameter version in bronze.

My task: to define the master geometry.

SLIDE-GUI for SLIDE-GUI for ““Pax MundiPax Mundi”” Shapes ShapesGood combination of interactive 3D graphicsand parameterizable procedural constructs.

Many Different Many Different Viae GlobiViae Globi Models Models

User-Guided Inverse 3D ModelingUser-Guided Inverse 3D Modeling

A generalized approach for obtaininga parameterized CAD model of a given artifact,given an unstructured mesh, a point cloud,or just a collection of images.

Model should use geometric primitivesreadily available in most CAD systems.

Important: Include the designer in the reverse-engineering loop!

Modular Reverse EngineeringModular Reverse Engineering

Extract a parameterized description, module by module.

In each case, the designer chooses a representation that best enables the intended re-design.

Use plausible, commonly used CAD constructs: CSG

Quadrics

Extrusions

Rotational Sweeps

Progressive Sweeps

User-Guided Inverse 3D Modeling User-Guided Inverse 3D Modeling ( Jimmy Andrews( Jimmy Andrews’’ PhD thesis) PhD thesis)

Let the user select a high-level model structurethat is most useful for immediate re-design.

Initial artifact Redesigns enabled by different imposed structure

Option 1: Varying Rotational SymmetryOption 1: Varying Rotational Symmetry

3 fold 4 fold 20 fold

Extract one sector; collapse/expand in polar coordinates.

Opt.2: Editing as Surface of RevolutionOpt.2: Editing as Surface of Revolution

Mesh is rotationally collapsed to yielda compound “cross-section”;

This cross-sectioncan then be edited,and this will affectthe whole mesh.

Opt.3: Extraction as Opt.3: Extraction as a Progressive Sweepa Progressive Sweep

20-story Scherk chain

Revised trefoil sweep path

User-Guided Fitting ModulesUser-Guided Fitting Modules Stationary sweeps:

(Surfaces of revolution, helices, etc)

Progressive sweeps:

Quadrics:

Freeform surfaces:

CSG modules: …

… then assume point belongs to sweep.

If normal is perpendicular to velocity field:

(simple motion) (simple velocity field)

Defined by a simple sweep motion, with a fixed axis (e.g. revolution, helix, spiral)

Stationary Sweeps

Fitting Algorithm:Fitting Algorithm: Find velocity field that fits marked data points:

Minimize (subject to constraint):

Grow the region by adding more fitting points

Repeat (typically converges in 2-3 iterations)

[ Pottmann, Lee, and Randrup, 98 ]

Interactive Surface EditingInteractive Surface Editing• A rotational sweep around the z-axis is specified.• A “thick profile” is extracted by collapsing φ-component.

• Portions of the “thick profile” can be selected and moved;• the corresponding surface elements move radially:• (a) the whole nose and cheeks area is enlarged;• (b) only the nose is stretched.

(a) (b)

Progressive SweepsProgressive Sweeps More parameters: Make incremental local adjustments

Allow more complex cross-section transformations(translation, rotation, scaling)

User stroke provides initial guess

Fit by iteratively extending and optimizing

Progressive Sweep FittingProgressive Sweep Fitting

Starting from user stroke, optimize cross section

Iteratively extend and re-optimize

Stop when best further extension would have excessive error

[Andrews, Joshi, Sequin 2011]

Flexibility of Progressive SweepsFlexibility of Progressive Sweeps

Capture the parameterized procedural description that best fits the users re-design plans.

• Yellow strokes (#1) defines the start of a progressive sweep.• An optional 2nd stroke extends or restricts the sweep range.

Versatility of Progressive SweepsVersatility of Progressive Sweeps• Different starting strokes and different error tolerances result in a wide variety of possible extracted sweeps.

• Sweep path and profiles can be edited independently.

• Surface details with respect to the extracted sweep can be conserved and reapplied after any editing moves, or they can be ignored or smoothed out.

Preserving Surface DetailsPreserving Surface Details

• Modifying the sweep path & scaling,while preserving surface details:

System PipelineSystem Pipeline

Unstructured mesh

Unstructured mesh

PhotosPhotos

3D scans3D scans

Input Data

Editable Model

Editable Model

ModelHierarchy

& Re-fitting

Clean

User-guided fitting

modules

Nice rendering

Nice rendering

STL for RPSTL for RP

OBJ for CAD

OBJ for CAD

Redesigned output

The Main Message:The Main Message:

The (re-) designer knows best which internal representation is most suitable to make the intended design changes.

Give the designer a good interfaceto tell the reverse-engineering system which CAD module and what parametersshould be used.

Tower of Engineering (on 6th Floor Terrace)

Another reparameterized geometry