Hi Dave, just a note on this part:

> I say "strange" because selecting the bad ngon and flipping
> it did not fix the problem. But if you flipped it a second time,
> then everything was OK.

Yeah, getting that result is due to one of the bugs in Modo's OBJ importer.

In Modo's core functions, it is sensitive to which vertex of a polygon is set to the first one in the list of vertices.

Modo's core polygon normal calculator only looks at the edges radiating out from the very first vertex of the polygon in order to determine the polygon's normal. So with a complex n-gon, the first vertex must be set to a convex vertex in order to get the proper result.

As far as I can tell, Modo's OBJ importer fails to do that, which may result in an improperly oriented polygon in Modo.

When MoI exports to LWO format, it does this work to set the starting point of the n-gon to a good location for Modo/LightWave's orientation mechanism. So that's why this problem is avoided when using LWO export instead currently.


Since Modo has this sensitivity to which point is the first point, it would be a good idea for their OBJ importer to be aware of that and set the first point to match what their core engine expects...

But also another good improvement would be for them to tune up the core normal calculation so that it is not so sensitive to which point happens to be the first one in the list.

The reason why doing the flip twice works, is that there is a mechanism in Modo's flip function where if you do it the second time it will do some work to figure out a good start vertex for the ngon and rotate the points in the list so that one is first.

Some other discussion on this here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2039.5

- Michael