Hi PaQ,
> (The double flip trick works too in modo :))
I believe that is a pretty solid indication that the problem with the OBJ import is not picking the starting vertex of the polygon in the spot that suits Modo best.
The way that Modo's (and LightWave's) orientation mechanism works, it only looks at the edges coming off of the very first point in the polygon, and uses the cross product of those edges to get the orientation of the polygon.
That is just not a good method to use, it is too fragile on more complex n-gons because if that first vertex happens to be a reflex vertex instead of a convex one, it will be pointing in the reverse direction, and additionally with this method the normal is not even defined at all if the 2 edges coming off of it are exactly colinear.
Instead of that it is a lot better to use Newell's plane fit algorithm which takes into account all the points in the polygon and is not so fragile to behave differently depending on which point happens to come first.
Really it would be better for them to fix this in Modo's core orientation mechanism (rather than in the OBJ importer specifically) to make that less sensitive to which point happens to be the starting one of the polygon, that would prevent this same problem from popping up in other situations as well.
- Michael |
