Drake
Collaboration diagram for Detecting Contact:

Given two posed geometric shapes in a common frame, the collision detection system is responsible for determining if those shapes are penetrating and characterizing that penetration.

We won't go into the details of the how and why these techniques work the way they do, and, instead, focus on what the properties of the results of the current implementation are. It is worth noting that these some of these properties are considered problems yet to be resolved and should not necessarily be considered desirable.

  1. Between any two collision Elements, only a single contact will be reported.
  2. Contacts are reported as contact at a point. (This is a very reasonable assumption for smooth convex shapes such as spheres and ellipsoids where relative motion must inevitably lead to initial contact at a single point.)
  3. Surface-to-surface contacts (such as a block sitting on a plane) are unfortunately still limited to a single contact point, typically located at the point of deepest penetration. (That point will necessarily change from step to step in an essentially non-physical manner that is likely to cause difficulties.)
  4. A contact normal is determined that approximates the mutual normal of the contacting surfaces at the contact point.

Next topic: Computing Contact Forces