Surface Specification Solutions Sought

1. Surface Specification Solutions Sought • Sheet tracing • Identifiable as local maxima/minima, not boundary • Folded fabric • Nasal turbinates • Mostly-closed volumes; Digital endocasts • (Semi?)-automatically finding closures • Finding surfaces that only exist in the mind of the scientist…

2. Nasal turbinates Project with Tim Rowe (UT) and Blaire Van Valkenburgh (UCLA)

5. Airbag fabric

6. Airbag Folds • Phase 1: Find a good separator material • Need to keep plies distinct when folded together • Scanning conditions • 420 kV, 1.8 mA • Field of view 180 mm • Slice thickness 0.25 mm • Slice spacing 0.2 mm • 30s/slice

7. Airbag folds

8. Other difficulties • Most algorithms (i.e. Marching Cubes) trace interfaces, not local maxima/minima • Would provide a “hollow plane” • Thinness of sheet • Ensures gray levels inconsistent • Fouls up image processing for noise reduction

9. Airbag folds • Phase 2: Conversion to CAD • The tricky part No good threshold value

10. Airbag folds • Folded sheet traversal algorithm • Based on local moment of inertia

11. Algorithm Outline • Build using facets (triangles in 3D space) • Use voxel centers as vertices • Find first facet, and then grow out from each edge • Growth is normal to edge surface, and perpendicular to 3rd eigenvector of endpoints • Search cone to find best target (highest gray value) • Add best facet (highest gray new voxel) at each step • No concave angles between facets • After facet added, see if new voxel can resolve any other edges

12. Algorithm in action

13. Remaining issues • Speed • Substantial data sets would take hours • Filling holes • Avoiding ragged edges • ???? • As more data sets are tried, additional complexities may be revealed • Bag seams?

14. “Lunch bag” scan

15. Digital Endocasts

16. Your mission, if you choose…

17. Extra credit