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Published byElvin Row Modified about 1 year ago

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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…

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

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Airbag fabric

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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

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Airbag folds

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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

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Airbag folds Phase 2: Conversion to CAD –The tricky part No good threshold value

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Airbag folds Folded sheet traversal algorithm –Based on local moment of inertia

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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 3 rd 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

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Algorithm in action

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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?

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“Lunch bag” scan

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Digital Endocasts

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Your mission, if you choose…

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Extra credit

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