I would assume, at a minimum, that you need to reverse the winding of the triangles in a mirrored trimesh. Cheers, / h+ Flavien Brebion wrote: > Quick, but fundamental question. Is ODE supposed to work "as is" for > tri-meshes that have a symetry "applied" to the rotation matrix, as a > scale ( like (-1, 1, 1) ) ? >