GJK - from simplex to feature

Dirk Gregorius · Post by **Dirk Gregorius** » Mon Jul 02, 2007 1:35 pm

When I use GJK for distance computation on two polytopes I would like to know the features that contain the closest points. Can I extract this information from the current simplex or is it possible to track this information somehow during the usual GJK iteration?

John McCutchan · Post by **John McCutchan** » Mon Jul 02, 2007 8:06 pm

I have not done this -- but if your polytope support function also returns a feature id (perhaps triangle#), you should be able to store that in the simplex along side W,P,Q. Then you can extract the set of features from both polytopes from the final simplex.

Erwin Coumans · Post by **Erwin Coumans** » Mon Jul 02, 2007 9:07 pm

In collaboration with a game company, we've done this last year, to get the triangle index to allow for per-triangle friction values for convex polyhedra (it was already trivially supported for concave trimeshes).

They contributed this anonymously for the public Bullet version, but I haven't had bandwidth to integrate it yet. I barely have the bandwidth to discuss in-depth how we retrieved the info from the simplex solver (voronoi in Bullet's case), passed the info on, and did a lookup on each polytope to get the triangle (based on vertex ID, position and normal).

Erwin