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# Contact Normals

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Hi all, I''m half way through developing my own physics engine and have come accross ANOTHER problem. :-( The question is does anyone have a neat trick for calculating a suitable contact normal from a pair of intersecting triangles. Aswell as the tri geometry, tri velocities are olso available. Working out whether or not a point of one tri intersected another is a peice of cake... trying to work the edges isnt quite as straight forward. Any ideas?? Does anyone know how ODE does it?

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If you mean the edge of one triangle against the edge of another, I would think a simple cross product of the edges would give you a good normal. Or, if they are parallel, cross the edge of one triangle with the norm of the other.

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yeah i agree. given two edges the normal will be the cross product.

The problem is probably better stated as... given a pair of intersecting triangles, how do i decide whether a point/face collision occured or whether an edge/edge collision occured. If an edge/edge then which pair??

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quote:
Original post by Mr_Pinner

The problem is probably better stated as... given a pair of intersecting triangles, how do i decide whether a point/face collision occured or whether an edge/edge collision occured. If an edge/edge then which pair??

Whichever is the minimum distance. If you need functions to calc the minimum distance between vertex/face and edge/edge, check out www.magicsoftware.com

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