I am getting strange artefacts in an obj file exported from an MoI for use in Kerkythea. Keyshot shows similar problems if I use it to open the obj file. The object is a thin planar with many holes removed with the boolean tools (see attached) and although the holes are fine in MoI they end up squashed or angular after going through the MoI export. Any suggestions as to what I might be doing wrong? The 3dm model is rather large so I'd prefer not to post it here... Ultimately the thin plate with the holes in it is meant to be close to transparent, like a sheet of glass with holes in it.

Thanks
Dan

Hi Dan - that looks like a triangulation failure by those importers.

Are you exporting from MoI as N-gons? (that's the Output: option on the meshing options dialog at export time).

Some programs have difficulty dealing with complex N-gons (N-gon means polygon that has more than 4 points in it) that are made up of a whole lot of points and have concave shapes. Renderers will usually need to triangulate those n-gons at some point during rendering or import, and unless that triangulation process is done very carefully it is easy for it to have bugs that produce bad output with triangles kind of leaking to the "outside" of what is supposed to be the outer boundaries of the polygons.

To fix it, when exporting from MoI switch the Output: N-gons option to be Output:Quads & Triangles instead.

That will make MoI itself generate a triangulation of complex polygons instead of relying on the other programs to do it, and MoI should be able to do a better job of it.

Please let me know if using the "Output: Quads & Triangles" option does not solve the problem.

- Michael

Thanks Michael that seems to have worked. Incidentally, Keyshot seems to give better results importing obj files than 3dm files - spheres appear distorted in the latter but are fine using obj files. So that's another plus.

Cheers
Dan

Hi Dan,

> Keyshot seems to give better results importing obj files
> than 3dm files - spheres appear distorted in the latter but
> are fine using obj files.

Sounds like probably a bug in either Keyshot's 3DM importer or their NURBS meshing mechanism.

Spheres happen to use a particular feature of NURBS that are called "weights" that are not always used for just a general surface that is not an exact conic.

Probably the Keyshot importer is not handling surfaces with weights set on them correctly. If that's the case then you may find that cylinders have a similar problem because they use weights as well.

If you send them a bug report on that one (with a sample sphere file for them to reproduce the problem), that's probably something that is easier for them to correct than the n-gon processing would be.


But you're going to be better off using MoI to produce the meshing instead anyway. When you export to an OBJ file, you're using MoI to do the meshing rather than relying on the NURBS-to-mesh conversion in Keyshot.


- Michael

Hi

Kerkythea only use triangles.
So use "Triangle only" Output.

I've learned you absolutely can't trust the import meshing of most 3D apps.

...And a lot of 3D apps don't handle ngons well, if at all - ZBrush (painfully) is another app that doesn't work well with ngons.


As Michael mentioned, you have to let MoI generate the mesh (ngons if your target app supports them), quads & tris, or even just triangles in some cases to be sure that you get exactly what you see in MoI.

Even then, I've found that most of my apps (Lightwave, Softimage) don't properly handle the normal information that MoI provides to make the models look as smooth as they do when they're in the MoI viewport.


IMO, Cinema 4D imports MoI's OBJs the best, and I find Carrara 7 Pro surprisingly does a decent job as well (when I actually use it - haven't tried all cases).


-Will

My test:
Moi3 -> Export -> *. obj -> KeyShot -> Snapshot



But,
*.3dm and KeyShot ...seems to be a problem.
I sent a support request to KeyShot/Luxion.

Great job Ralf! Demonstating that a sqaure peg doesnt fit through a round hole?

BTW: One of the MOST powerful features of MoI is it's mesher. Your benefit would be to do your meshing with MoI then send it out to a poly app. Some people buy MoI JUST just to mesh their output, though I think they then start to model with it too after they realize it is not a "Toy".

Good luck.

[EDIT] I posted as if you were DAN the original poster. Not paying attention. It appears as some kind of demonstration to filter molecules.[EDIT]