[ODE] Location of contact points

[Michael Lacher]

Hi!

   I try to write my own collision detection code for use with ODE. I 
have a question regarding the location of contact points and the 
direction of the normals.

I have looked at how ODE positions the contacts and i found the 
following two cases:
* For boxes the contact points are always on the boundary of one of the 
boxes, and the normal is the normal of the box face.
* For spheres the contact point is always the center of the circle where 
the two sphere surfaces intersect, and the normal is the normal thereof.

My questions are:

* Is it more correct to have the contact point always on the surface of 
at least one of the volumes ? or is it better to have it kind of "in the 
middle" if the volumes overlap" ? (how does this decision affect the 
physics simulation? )

* If two boxes overlap with one corner each, what is the correct contact 
normal ? should i try to find some kind of "secant plane" or just use 
any normal ?

regards
mucki