Hi Metin,

Thank you very much for your indication!

P.S. Michael, could you please explain more in depth what "CentroidTriangulation" is and how it woks ?

Nice day,

- Marco (mkdm)

My pleasure Marco. Always glad to contribute to the generous MoI community.

Hello,

I think (need confirmation) that CentroidTriangulation=y by default.
I have disable it too because sometimes it can introduce render artifact when dealing with very long skinny polygons in the meshing. (mostly happens in fillet area for me)

http://moi3d.com/forum/index.php?webtag=MOI&msg=3533.14

For Zbrush, I prefer to use the 'tris and quad output', and using the 'divide larger than' parameter as low as the memory usage allow.

Thanks for the addition, Pascal. I also use the 'Quads + Triangles' option and 'Divide larger than' set to 'All' when exporting for ZBrush.

I'll add this to my initial post, for more completeness.

Hi PaQ,

> Thanks for the addition, Pascal. I also use the 'Quads + Triangles' option and 'Divide larger than' set to 'All' when exporting for ZBrush.

Me too, for exporting to 3DCoat, use 'Quads + Triangles' option and 'Divide larger than' for 'All',
and I never had a problem with that settings.

Nice day,

- Marco (mkdm)

@metin, re:
> Michael, maybe it's a good idea to add the Centroid triangulation option as a checkbox to
> the mesh export options of MoI V4, to make it more accessible? Thanks in advance.

Yes, that sounds like a good idea to add for V4, if you can remind me about it again when v4 starts up I will add it in.


@ Marco, re:
> P.S. Michael, could you please explain more in depth what "CentroidTriangulation"
> is and how it woks ?

I'll post an example shortly.


@ PaQ, re:
> I think (need confirmation) that CentroidTriangulation=y by default.

It was on by default for Moi v1 and MoI v2 but off by default starting with MoI v3 since introducing an additional center point in lower poly meshing tends to be undesirable because it disrupts the regularity of the shape. The center of each n-gon area can kind of pop out too much. It works best when there's a higher polygon count with more uniform dicing.

- Michael

Hi Marco,

re:
> P.S. Michael, could you please explain more in depth what
> "CentroidTriangulation" is and how it woks ?

It comes into play when you're exporting using "Quads & Triangles" or "Triangles only" modes. The way the mesher works is it starts by making a grid of quads along the "underlying surface" of each face. Then any trim curves on the face will cut any quads they cross into n-gons. If you're exporting n-gons those are directly exported but if you're using "Quads & Triangles" or "Triangles only" modes, the n-gons need to get converted into triangles. If "CentroidTriangulation" in moi.ini is turned on, then it will test if making a center point for the n-gon and making triangles radiating out from that center point is a valid triangulation and if it is use that way. Otherwise without centroid triangulation no center point is added and triangles are formed only between the outer points of the n-gon.

So for example with an n-gon like this:



With centroid triangulation enabled it will add a center point and make a triangulation like this:



Without centroid triangulation, no center point will be added and only the points along the n-gon boundary will get triangulated which will look like this, which has even skinnier triangles than the centroid one:



So in the above case centroid triangulation is probably better.


Where it doesn't work so well is in low poly count situations, especially where the n-gon doesn't happen to have any points vertically aligned with the center like this:



Centroid style:



Non centroid style:



When there's a low poly count the center point which goes on the actual point of the original curved surface tends to be a little distance away from the other points and connecting triangles to it tends to make each n-gon sort of like a little pyramid in shape, which kind of introduces a bad pattern in the poly formation. That's why it's off by default now.

If I remember right I think it was originally added specifically to make meshes that worked better with ZBrush. http://moi3d.com/forum/index.php?webtag=MOI&msg=4978.41


Also see here for a previous example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3533.14

- Michael

Very useful tip. Thanks a lot!

Michael: Can you put a certain setting into the export settings pop-up window? The user should be able to choose between non-centric and centric on a per-export object basis. Would be very useful.

Hi 3image,

re:
> Michael: Can you put a certain setting into the export settings pop-up window?

Yes, if you can remind me about during the v4 beta release cycle I can add it in.

- Michael

Hi Michael,

I wish to thank you for your exhaustive and very clear reply!

You're a perfect teacher.

Nice night.

- Marco (mkdm)

Many thanks for your very informative explanation of the way centroid triangulation works, Michael, much appreciated.

I will try to remember repeating my request for centroid triangulation as a mesh export option when MoI V4 has 'surfaced'. ;-)

Added this extra ZBrush tip to my initial post:

I assign differently colored styles to key surfaces in MoI, and import in ZBrush using the option to import Obj materials as polygroups. Then I use those polygroups as ZRemesher guides by activating the KeepGroups option.

very useful feature! just can't find moi.ini
where it is?
PS: I found 4 files in different locations. which one should I choose? Application data or AppData/Roaming?

Hi gmlr,

Try C:\Users\<usr name>\AppData\Roaming\Moi

Best,

- Marco (mkdm)

thank you!

Non-centric vs centric ? Does it make any difference when exporting STL for 3D printing?

Ed Ferguson

Hi Ed,

Good question. I don't know if the two triangulation methods only divide quads in a different triangular way (then there would be no or almost no visual difference in the polygon structure), or if they each result in a visibly different triangular polygon structure.

I hand over the microphone to Michael for this. :)

Hi Ed, centroid triangulation shouldn't make any difference for 3D printing - ZBrush seems to be sensitive to the triangle structure.

But one thing that I think is good for both ZBrush and STL export is to use the "Divide larger than" option which will chop up anything larger than the distance you put in there. It can be good for both of these exports to try and avoid having triangles span a large distance across the object, it tends to make the triangulation more apparent in the final result. ZBrush needs a finer level of dicing though.

- Michael

@Metin, this setting won't change how quads are triangulated, just n-gons which you'll get at trimming boundaries.

- Michael