Okay, double posting here on purpose to share what my experiemnts while working at the turntable taught me about tags: The direction from vertex 2->0 equals +X direction, 2->1 equals +Y and normal direction equals -Z. Angles withing the triangle are completely ignored, the only thing that matters are vertex indices and their relative positions to each other. Depending on your software the indices might be different in your software. 3ds Max ,for example ,starts counting from 1 instead of 0 while softimage seems to have reversed vertex indices.