Hi andrew,

> Hi Michael - my other choice for a 3D package was Cinema4D,
> but from this thread:
> http://moi3d.com/forum/lmessages.php?webtag=MOI&msg=3869.65
> it looks like n-gon output doesn't work either.

Usually n-gons work well in Cinema4D, but there are occasional similar problems. As far as I can tell the problems are pretty rare.

If you're looking for a program that handles every kind of n-gon 100% of the time without even any possible exceptions then no I suppose that does not exist.

But also usually people don't seem to run into so many problems with Modo either though.

Usually with either Modo or Cinema4D you can use n-gons most of the time and then for cases where you're running into some problems use Quads & Triangles for those particular cases.


> A quote from the page:
> http://www.luxology.com/store/CAD_Loaders_for_modo/index.aspx

Definitely try it out for yourself first - I've heard from people that were using it during its beta release and were not at all impressed with the n-gon output. From what I could tell it looked pretty much like they took triangulated output from the CAD kernel and just attempted to assemble those triangles into n-gons, instead of actually natively generating n-gons as part of the tessellation process.

But it's definitely worth checking out.

- Michael

Moi3d -> C4D works more than great. See attachment.




The only thing is that you cant put a Modo mesh in a C4D Hypernurb. Although I don't think this is something you've planned.



Peace,
Rich_Art. ;-)

Hi Andrew,

I was on the beta of the CAD loader.

The target of the product is CAD users coming from the solidworks world, that need to get their cad data into Modo.
The plugin for example manage instances, meaning you can reduce memory usage a lot in some situation. There is also
a light curve display mode that can help to handle huge model inside Modo.

Now as an exclusive MoI user, it's an other story.

First, I can tell you, nothing can beat MoI ngones output for the moment ... You seems as picky as me about micro details, you will probably loose your hair here with the cad loader.
You can say, from your knobs test here, that ngones dont work well in modo. I respect the pov, but I will continue to use the ngones export. I have render many models at print size, and it's really hard to notice those micro glitches. (In fact I miss them until your post here).

Second, if you come from MoI, you have to deal with .igs or .stp format, and that gives a lot of troubles on the table too compared to a true .3dm loader (or a MoI poly export). Be prepared to have disconnected fillets, holes, inverted or missing surfaces (bad trimming) etc.

I have seen outstanding result with Cad loader, many people are really pleased of the product compared to something like polytrans.
I wasn't that lucky with my models so far.

I think you can request a demo of cad loader now, but I'm affreaid you need at least a 601 licence (601 demo is not out yet).

Hi PaQ, I have Modo 601, and a trial of the CAD loader. It did not generate a mesh with "all quads" at all, but loads of triangles. I could get the areas of triangles smaller by forcing a maximum length to the lines so it would dice things up more, but wanted to show here the results without that. The CAD loader did generate a mesh with good topology for reflections, but the bump mapping problem still remains at the corners. In the end the CAD loader n-gon output is quite similar in complexity to the MOI quads+tris output, but the MOI one is better since the bump mapping works. So MOI quads+tris is the best solution for use with Modo.

Hi andrew, from what I can tell there from your example that the Modo "CAD loader" generated, they really shouldn't be claiming that it actually generates quad - n-gon meshes if that's the result that they actually make.

It really looks to me like they just are taking a triangle mesh that was initially generated by the Parasolid kernel and then just trying to glue those triangles together into n-gons and that makes a kind of chaotic looking n-gon result and can still leave a lot of triangles at the end as well.

- Michael

Andrew,

I still cannot reproduce the errors you are getting in Modo. Could you upload the .lxo file so I can compare it with mine?

Hello guys, Hi Michael

About : CentroidTriangulation

I have some time to waste, so I decide to start a discussion about this Modo internal triangulation problem (on modo beta forum), with good examples etc.

Because I have a new computer here, I had to re-install MoI, and I start some export test, and ... I get all kind of ugly shading glitches when using 'only triangle' in MoI export.

Hopefully the 'deja-vu' result makes me remember this famous 'CentroidTriangulation' option, ... and as expected, if I disable it, everything comes out perfectly.

 

But I'm wondering, why is this option ON by default in MoI .ini ? , because it introduces so many glitches when using triangles only export, especilay in fillet area ?
Is there any example where this option creates 'better shading' result, using triangles only export ?

@PaQ not about this centroïd
Do you know this French Modo forum ? http://modo.logy.fr/

Hi PaQ - can you post some more information about the ugly shading glitches with "triangles only" part with centroid triangulation enabled? Is it with a somewhat rough/low poly count type mesh generation?


> Is there any example where this option creates 'better shading' result, using triangles only export ?

re: Centroid style on by default - it's more about polygon structure for stuff like displacement I guess, not so much shading specifically.

For some situations it makes a much cleaner mesh structure with the centroid style triangulation, the best example is the top cap of a cylinder, if that is meshed with a centroid point added to the center like slices of pie, it makes for all regular shaped triangles. If it is triangulated using only by connecting together points on the outside of the n-gon then the triangles will kind of zig-zag across the face and will be of different sizes. But actually MoI analyzes the n-gon and if it is an exact regular polygon shape like a cylinder end cap it will use centroid style on it no matter what.

Let me see if I can find the thread that got me started with turning centroid triangulation on by default for other cases as well... I think someone mentioned that ZBrush triangulated all n-gons that way and that they liked that type of polygon structure better.... Ok here it is:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1024.1

I guess the main reason is that it tends to make kind of more squat triangles instead of longer skinnier triangles. The downside can be with lower density meshing it basically introduces a new sample point in the middle of the polygon and when that is evaluated on the actual curved surface it can make a kind of "poking out" spot...

- Michael

Hi Michael, here's an exemple ...



Mostly every fillets show some glitches , a bit like the previous posts I made.

It's not a really big problem as I know how to resolve it (editing the .ini, using subdivide larger than option, etc), but in the other hand I expect 'triangle only' to produce the best shading quality possible and I would not really care that much about 'topology aesthetic' in that export mode ... dont you think ?


@Pilou, thanks for the link, I have follow a webinar last time with greg from luxology, really great to hear some french :)

Hi PaQ, so that's basically that same "low polygon" density kind of problem that I was describing earlier - the fillet piece there gets a low number of divisions along one direction despite the angle setting of 6 because the angle setting is based purely off of curvature and will not divide things that are very shallowly curved but long.

What you get in that case is an n-gon that's pretty non-planar and then introducing a centroid point in the middle of that does not work very well.

The real fix is probably more like adding in some additional refinement mechanism that kicks in automatically to avoid making a pretty non-planar n-gon to begin with. Basically if your n-gons are not torqued then centroid triangulation would not cause that kind of problem.

Right now for that kind of geometry you have to use those various additional settings like "Divide larger than" to force that fillet to get subdivided more in the long direction than what is currently happening by the angle measurement alone. On shapes that are shallowly curved like that you basically will get low-poly artifacts even with a high angle setting.

Non-centroid triangulation does tend to not mess things up on non-planar n-gons as much as centroid ones do, but it's still better for those types of things to get subdivided more overall so that the final n-gons that get triangulated are not so non-planar in the first place.

But part of the difficulty though is that the non-planarity of the n-gons isn't really there during the subdivision process itself which works only on "underlying surfaces". In a case like you have here the non-planar n-gon is formed only after the trimming boundaries are introduced onto the surface, that happens after the subdivision process is all complete so it's not very easy for the subdivider to take that in particular into account at least with the current architecture. But some other metric that would look for things that were fairly long but only shallowly curved and divides those surfaces additionally would help, it's just that some of these things like what exactly "fairly long" means in some algorithmic way that applies to any kind of model is kind of difficult to quantify. And also it's a problem for actual desired low poly output if something kicks in with too many subdivisions totally automatically.


Anyway, to make a long story short - in your model here your fillets are getting low-poly artifacts on them because they are not divided enough in their long directions, they need to get divided more to make the n-gons less warped and once they are divided more either centroid or non-centroid triangulation will work ok on them. Right now you have to force such subdivisions yourself by using some of those other settings, I do not yet have an automatic way of ensuring that this kind of situation gets automatically subdivided.

- Michael

Hi Michael,

- The real fix is probably more like adding in some additional refinement mechanism that kicks in automatically to avoid making a pretty non-planar n-gon to begin with. Basically if your n-gons are not torqued then centroid triangulation would not cause that kind of problem.

Would be indeed great if that kind of problem can be fixed in an 'automatic way' without adding to much geometry.
Maybe I'm too greedy about polycount too :)

Hi PaQ,

> Would be indeed great if that kind of problem can be fixed in an 'automatic way'
> without adding to much geometry.
> Maybe I'm too greedy about polycount too :)

That "not adding too much" part is where it gets particularly tricky, especially trying to come up with a mechanism that can gradually do it in increments along with the slider being moved...

In the meantime maybe it is best if I turned centroid triangulation off by default since it has a tendency to not handle these types of situations very well. Another thing I was thinking about was to maybe have it turn off when the base n-gon was over a particular aspect ratio like 10 to 1 or so...

- Michael

Hi Michael,

Yes this centroid triangulation is, from my pov, a little problem, especially since this thread.

I was about to suggest some modo users to use triangle output format if they really want to get the best possible
shading out ot MoI (until modo can handle ngone tesselation better, not a MoI fault here).

But having to edit the moi .ini file to avoid glitches from this centroid triangulation can look a little bit tricky too.

Well that's up to you now !