1. Adobe Retreat, November 12, 2013 Weak Links in the Chain from Concept to Construction Carlo H. Séquin University of California, Berkeley

2. 40 years of making use of CAD CCD TV Camera (1973) Soda Hall (1992) RISC 1 MicroChip (1982) Octa-Gear (2000)

3. Recent Designs and Models

4. From Concept to Construction u A vague idea in your head u A sketch that can be shown to others u A first version of a geometrical model u A parameterized CAD model u A fine-tuned version u A file for an RP machine u A tangible RP model u Final scale model u The real thing PART 1 PART 2

5. Talk Outline PART 1: Concept Input u Creating Parameterized CAD Models u  User-Guided Inverse 3D Modeling PART 2: Obtaining Tangible Output u Slicing Imperfect.STL files u  Relying on the Winding Number

6. PART 1 How to get started ? How to get your ideas into the CAD system? Most design activities do not start from scratch! A predecessor model needs improvement An inspirational artifact stimulates a new design

7. “Hyperbolic Hexagon” by B. Collins u 7 tunnels in a disk u 4 boundary curves u approx. minimal surface Aims: u Increase complexity u Maximize aesthetics -- from all directions!

8. Closing the Loop straight or twisted “Scherk Tower”“Scherk-Collins Toroids”

9. Sculpture Generator I, GUI

10. Shapes from Sculpture Generator I

11. The Finished Heptoroid u at Fermi Lab Art Gallery (1998).

12. Brent Collins’ “Pax Mundi” 1997: wood, 30”diam. 2006: Commission from H&R Block, Kansas City to make a 70”diameter version in bronze. My task: to define the master geometry.

13. SLIDE-GUI for “Pax Mundi” Shapes Good combination of interactive 3D graphics and parameterizable procedural constructs.

14. Many Different Viae Globi Models

16. User-Guided Inverse 3D Modeling u A generalized approach for obtaining a parameterized CAD model of a given artifact, given an unstructured mesh, a point cloud, or just a collection of images. u Model should use geometric primitives readily available in most CAD systems. u Important: Include the designer in the reverse-engineering loop!

17. Modular Reverse Engineering u Extract a parameterized description, module by module. u In each case, the designer chooses a representation that best enables the intended re-design. u Use plausible, commonly used CAD constructs: l CSG l Quadrics l Extrusions l Rotational Sweeps l Progressive Sweeps

18. User-Guided Inverse 3D Modeling ( Jimmy Andrews’ PhD thesis) u Let the user select a high-level model structure that is most useful for immediate re-design. Initial artifact Redesigns enabled by different imposed structure

19. Option 1: Varying Rotational Symmetry 3 fold4 fold20 fold Extract one sector; collapse/expand in polar coordinates.

20. Opt.2: Editing as Surface of Revolution Mesh is rotationally collapsed to yield a compound “cross-section”; This cross-section can then be edited, and this will affect the whole mesh.

21. Opt.3: Extraction as a Progressive Sweep 20-story Scherk chain Revised trefoil sweep path

22. User-Guided Fitting Modules u Stationary sweeps: (Surfaces of revolution, helices, etc) u Progressive sweeps: u Quadrics: u Freeform surfaces: u CSG modules: …

23. … 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

24. Fitting Algorithm: u Find velocity field that fits marked data points: Minimize (subject to constraint): u Grow the region by adding more fitting points u Repeat (typically converges in 2-3 iterations) [ Pottmann, Lee, and Randrup, 98 ]

25. Interactive 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)

26. Progressive Sweeps u More parameters: Make incremental local adjustments u Allow more complex cross-section transformations (translation, rotation, scaling) u User stroke provides initial guess u Fit by iteratively extending and optimizing

27. Progressive Sweep Fitting u Starting from user stroke, optimize cross section u Iteratively extend and re-optimize u Stop when best further extension would have excessive error [Andrews, Joshi, Sequin 2011]

28. Flexibility of Progressive Sweeps u 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 2 nd stroke extends or restricts the sweep range.

29. Versatility 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.

30. Preserving Surface Details Modifying the sweep path & scaling, while preserving surface details:

31. System Pipeline Unstructured mesh Photos 3D scans Input Data Editable Model Model Hierarchy & Re-fitting Clean User- guided fitting modules Nice rendering STL for RP OBJ for CAD Redesigned output

32. The Main Message: u The (re-) designer knows best which internal representation is most suitable to make the intended design changes. u Give the designer a good interface to tell the reverse-engineering system which CAD module and what parameters should be used.

33. u Tower of Engineering (on 6 th Floor Terrace) Another reparameterized geometry