1. Representation Issues in Data Exchange for RP-LM Sara McMains U.C. Berkeley

2. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

3. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

4. Data Translation Easiest for the designer: –Format that includes all design constructs B-reps –Tesselated –Trimmed NURBS CSG Sweeps Voxels Parametric Surface equations

5. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

6. Data Translation Easiest for the manufacturer: –Simplest possible format Lowest common denominator This is why STL is still being used!

7. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

8. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

9. ASCII or Binary? ASCII –Data exchange always imperfect Humans will end up examining files Binary –Compact –Computers store binary numbers Simple fractional decimals cannot be exactly represented as floating point values

10. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

11. Sources of Cracks in STL Round-off –Instancing with geometric transformations

12. Require Shared Vertices Specify vertex coordinates only once All geometry that shares vertex references same vertex Compact for transmission Forces designer to think about connectivity

13. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

14. Sources of Cracks in STL –Boolean trim curves

15. Boolean Trim Curves Intersection curve higher order than input Mapped back onto input patches –Approximated in parametric space –Won’t match exactly on two patches Connectivity of trimmed patches should be specified explicitly

16. File Repair Techniques: Local Triangulate between unmatched facet edges –Bohn and Wozny ’92 –Barequet and Sharir ’95 Merges edges for small cracks, Triangulate remaining holes –Barequet and Kumar ’97 Adding triangles may introduce intersections; Best match problem NP complete

17. File Repair Techniques: Global Build a Binary Space Partitioning tree, identify solid regions, output boundary –Murali & Funkhouser ’97 Scalability issues

18. Better STL Generation Curved patch to STL conversion without gaps: Match discretized trim curves, User-supplied tolerances –Dolenc ’93 –Sheng & Meier ’95 Prevent intersections when triangulating

19. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

20. Nesting Information Should nesting of shells be transmitted? –Designer intent –But how is nesting generated? Computed from b-rep? –What if it disagrees with geometry? Who do you believe - geometry or topology?

21. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

22. Units Require units! Lack of units invites educated guesses Default unit not good enough –Assumptions may differ –Require explicit specification Force assumptions to be visible

23. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

24. Input Captured in Layers E.g. –CT scans –Digitized input Can we manufacture these layers directly? Do we want to?

25. Matched Layer Thicknesses

26. Unmatched Layer Thicknesses

27. Surface Reconstruction Interpolate between input slices –Interpolation smooths boundary –Additional processing can further smooth coarse input –Complete freedom to re-orient surface Faster build times

28. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit

29. Implicit Booleans Implicit unions

30. Implicit Booleans Implicit unions

31. Implicit Booleans Implicit differences (2D example)

32. Implicit Booleans Implicit differences (2D example)

33. Implicit Booleans Implicit differences (2D example)

34. Implicit Booleans Implicit differences (2D example)

35. Implicit Booleans Implicit differences (2D example)

36. Implicit Booleans Implicit differences (2D example)

37. Implicit Booleans Implicit differences (2D example)

38. Implicit Booleans Self-intersections (2D example)

39. Implicit Booleans Self-intersections (2D example)

40. Implicit Booleans Self-intersections (2D example)

41. Implicit Booleans Even if exchange format doesn’t include explicit Booleans, implicit Booleans will arise Manufacturers won’t categorically reject Need semantics for implicit Booleans

42. non-2-manifold Scope: Solids Optimize for 2-manifolds –2 directed “edge-uses” per undirected edge Should also support non-manifold solids 2-manifold

43. Pseudo-2-Manifolds Geometry not 2-manifold Represented topology is 2-manifold

44. RP-LM Data Exchange Designer Read Validate Scale Position/orient Slice Rasterize Manufacturer Network Translate Write Transmit