> But generally Modo is pretty good in this area, its n-gon triangulation failures tend to be pretty rare, and small in number.

> If you can isolate it down to a small example, it would probably be good to send it to luxology so they could do something to fix it up.

Well, after reading Frenchy Pilou's suggestion, I decided to try a create a simple failure case to send you. The good news is that everything I tried worked fine (sort of). So it is not what I thought it was (simple non-convexity). The "sort-of" qualifier refers to the fact that I could consistently create cases where the ngons were there, but in some kind of a strange "flipped" state. 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. That's not such a horrible problem, because it only takes a couple of seconds to fix (once you know to "flip it" twice). However, I'll try and send the example to Luxology to look at.

So then I went back to the original, more complex, MoI file that I had observed having a real problem when loaded into modo. Well, the file had a problem when loaded back into MoI as well. There were some strange faces sticking out of the geometry in a couple of places. Zooming into the nook and crannies, I noticed that I had probably applied a slightly too large fillet around the edges of some text I had booleaned into an object, and in some of the corner creases it was causing some problems. Didn't really see it when I applied the fillet though. So I guess it was my bad after all.

> One other thing you might try when you run into this (which should hopefully be only an occasionally seen thing rather than the norm) is to use the "Divide larger than" parameter in MoI to dice polygons up and alter their structure. If you enter in a distance for "Divide larger than", any polygons larger than that size will be diced down, which tends to also cut complex n-gons into less complex n-gons.

Yes, this is a great feature that I have already had occasion to use. I had created a surface with a very subtle curve that ended up being a single ngon on export. Since I didn't want it to appear to be perfectly flat, I began experimenting with some of the "slice and dice" features in the dialog and quickly solved the problem. Like you said, you probably don't need to use them often, but it's really nice having them there when you do.

> Yeah, I would like to have this in the future... It's unfortunately not always so easy for me to get this information, often times the operation that failed is some low level thing way deep down in one of the geometry library's algorithms and it is not easy to try and record the specific problem all the way from the "top level view" from the code...

Oh, I see. I had forgotten that most of your code is sitting on top of a 3rd party library. Well, you can always give an error similar to one that one of the C compilers back in the 80's used to give me: "Syntax Error: Program expected." ;-)

Dave Morrill