A CAD model created with ACIS and tessellated by I-DEAS.

Here is a schematic of its medial axis. The seams are represented by straight lines.

The symmetry makes this example challenging for a continuous algorithm. The medial axis has several degenerate junctions, shown in red.

You can see that a few seams are missing. These are the seams with two degenerate endpoints. The current implementation can trace only the seams with zero or one degenerate endpoints.

The problematic symmetry is not due to the geometry of the model. Rather, it comes from the identical subdivision of the non-convex faces on the top and bottom of each arm. In other words, the model itself has a non-degenerate medial axis, but the tessellation creates degeneracies.

Tim Culver
Last modified: Tue Aug 29 22:13:54 EDT 2000