Re: Is this 3D GJK intersection test code correct?

2013-06-17T17:40:23+00:00

The termination condition looks questionable. Termination for GJK is hard to get right. Back in the 1990s, Steven Cameron at Oxford and I struggled with this. See his web site for the code.

It's possible to get into states where the solver is moving through a sequence of adjacent supports. Are you exiting at

Code:

if(loopCounter > MAX_ITTERATIONS)                break;

If so, collision is undecided. Note when you exit there.

Objects for GJK need to be really convex. Coplanar triangles are a no-no, because they create ambiguity over which face belongs in the simplex. So you can't just use triangle meshes; you have to handle arbitrary polygons. In my Falling Bodies system, I used QHull to construct convex hulls, and required that there be at least a 1 degree angle across each edge. This guarantees convexity.

Single precision GJK is flaky. Use 64-bit floats. If you're using GJK in a physics engine, some objects will settle into the face-parallel condition, which results in small differences between large numbers and can lead to total loss of significance in 32-bit.

Statistics: Posted by John Nagle — Mon Jun 17, 2013 5:40 pm

Is this 3D GJK intersection test code correct?

2013-05-31T10:25:51+00:00

Hi there,
Here's the link:
https://github.com/ChrisLundquist/CS143 ... mplex.java
I've recoded it in my application, but sometimes I'm getting false positives, while the other GJK implementation seem to be working fine.
What might be wrong with code from link? Is it my fault or it's there a bug?
Any help is welcomed

Statistics: Posted by ConvexHull — Fri May 31, 2013 10:25 am

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Re: Is this 3D GJK intersection test code correct?

Is this 3D GJK intersection test code correct?