Hello!!! just new user of Moi, (but used of rhino already)... what are the advantages of using the different sort of export: ngons, quads and triangles, triangles?... and a pure quads export is, I suppose, as in rhino, impossible?...

Hi Marcel, it depends on what you are going to be doing with the mesh and what software you are exporting to.

But in general if your target software supports n-gons it means that you will get a clearer looking wireframe structure using that option.

The n-gon output will generate multi-sided polygons in areas that have trim curves (basically where booleans have happened).

Here is an example, here I have taken a sphere and booleaned a hole out of it:



If you save this to a mesh format, if you use the n-gons option you will get a result that looks like this:



Here I have marked how an n-gon is formed in that spot where the hole was cut, you can see that the polygon is made up of many segments there:




Now when you open such a mesh in Cinema4D for example it looks like this:



The mesh just has a cleaner wireframe that much more closely resembles the original NURBS object rather than being chaotic.

Here's an example in Cinema4D of a more complex model meshed with n-gons:




However, not every program supports n-gons properly, so if you are exporting to a program that does not process n-gons well, then you will need to use the Quads & Triangles option usually. You would generally only want to use "triangles only" for special purposes if your target program does not even support quads but that is uncommon.

If you let me know which program you intend to export to it may help to give more specific advice.


> and a pure quads export is, I suppose, as in rhino, impossible?...

It can work in some special cases like if you have objects with uniform curvature such as a surface of revolution that does not have odd areas booleaned out inside of it.

But for a totally general solid that has trim curves in it, no you won't generally get all quads from it.

Getting all quads would require tiling areas in a different way than MoI's mesher currently works, for some recent discussion see here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2451.50

- Michael

@Marcel: le Marcel? (ZB, Polyloop etc...? ;)

If yes, there is also the French Moi forum here (by Bibi pour les tuyaux basiques) but of course best advanced technical advices will be done by Michael here :)

This guy is a 3D / 2D master all progs !
By Marcel ;)

Thank you for your answer!... mainly, the software where I want to export is modo... I have noticed that a complicated mesh from rhino, textured as glass, so transparencies and refraction, was very very time consuming to render, and a sort of "same shape" mesh, directly done in modo, was , with same material, much fastyer to render... So I think that the resulting mesh of the nurbs process is important, and I suppose modo allows ngons... I'll try today ( buy Moi very late yesterday)...
One curiuous thing I noticed, just trying Moi and importing a file from rhino, was the handle of nurbs objects from Tsplines... seems to be imported "before" trhe translation in current nurbs, but I have to test more intensively... Love also the instinctive feeling of Moi, although that the fact to know rhino is probably an help!...
and yes, FP, I'm probably the only one with that firstname in 3d field... there is a french forum already?...

<there is a french forum already?

Yes, up right top page :)
Pour les décalages horaires :D

Bonjour Marcel, yes N-gons usually work well with Modo, there are quite a few people that use MoI to export N-gon meshes to Modo, most often with the .lwo file format.

However, just n-gons themselves (as opposed to Quads & Triangles) won't particularly speed up your renderings, that part will be roughly the same between those 2 options (whether you set Output:N-gons or Output:Quads & Triangles). Render speed is more about the density of the vertices that make up all your polygons rather than if they are n-gons or triangles.

However, MoI's mesher does some work especially on mechanical parts to make a good looking mesh with not quite as much overall polygon density, especially on things with regular curvature such as cylinders and spheres. This is kind of a separate thing from using n-gons or not. But anyway, here are a couple of messages on one person's experience with that:
http://news2.mcneel.com/scripts/dnewsweb.exe?cmd=article&group=rhino&item=283096
http://news2.mcneel.com/scripts/dnewsweb.exe?cmd=article&group=rhino&item=283169
A quote from the above: "I made an ultra detailed Roman catapult, at 450k poly's it's just too heavy to sell, really, and reducing further wrecks the fine quality, but MOI can do it in half the polys which is great and same quality."


But I guess if you are using T-splines you are probably doing some irregular types of shapes rather than mechanical shapes, so it is possible that you may not see quite as large of a difference as you would with regular shaped things. Certainly worth a try though!


> One curiuous thing I noticed, just trying Moi and importing
> a file from rhino, was the handle of nurbs objects from
> Tsplines... seems to be imported "before" trhe translation in
> current nurbs, but I have to test more intensively...

I seem to remember that you may need to switch to a certain T-splines mode for the plain NURBS surfaces to be available in the file... Something like that anyway. You'll need to do whatever you would normally do to be able to send the T-spline model to someone else with just plain Rhino that does not have the T-splines plugin.

Some discussion on that in this thread, maybe it will help:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2359.1
http://moi3d.com/forum/index.php?webtag=MOI&msg=2359.8

Otherwise you may need to ask the T-splines people what you need to do to make the T-spline object stored as a regular NURBS object (rather than as special data that only their plug-in knows about) that other programs can read.

- Michael

"One curiuous thing I noticed, just trying Moi and importing a file from rhino, was the handle of nurbs objects from Tsplines..."

If you like to render the T-Spline objects at Modo, than I would use the T-Spline mesher. This mesher create nice homogeneous meshes direct from T-Spline objects.