Hi Michael, I guess the "non centroid triangulation" tri-export will showcase those tiny triangle connection problem in any render engine really, especially on reflective surface, but also on self ray-trace shadow (along with the usual shadow terminator problems).




... once centroid option is activated everything is fixed.



Do you think the Ngones .FBX internal triangulation could benefit from this centroid triangulation too ? I don't trust my Hou setup that much :P

SketchUp was never really designed to have curved objects in it at all. There isn't any way (at least last I checked in the SDK) for it to contain vertex normals so it's inevitably going to have shading problems.

However, with this particular case it looks like maybe the skinny triangles might be reversed as well. That may be the larger problem.

re:
> Do you think the Ngones .FBX internal triangulation could benefit from this centroid triangulation too ? I don't trust my Hou setup that much :P

I guess so but that would be a long process to try and get Autodesk to change that.

I kind of remember there may be an option to supply a triangulation, maybe I should do that.

- Michael

I see, I didn't know that would involved Autodesk :S

Hi rom, so it's not that the skinny tris are reversed exactly, it's that the n-gon that they are carved off of is non planar enough that they are ending up pivoted quite a bit.

Here's what I mean, this is a side view of one of them:





Then it seems like your render engine does not like having a little face that has a face normal deviating quite a bit from surrounding other face and vertex normals, it probably gets the surrounding area dark by thinking it's in a shadow. (if there is an option for raytraced shadows bias factor bumping it up could reduce this "self shadowing" effect)

Was this fillet made in MoI v5? It kind of looks like there is just a little too much of a gap between the fillet surface and the cylinder which looks like it contributes to making the n-gon more non-planar. If this is coming from the new ACIS fillets in MoI v5 it would probably help if I tightened up the fitting accuracy for the conversion from ACIS just a little bit more.

If you turn on the moi.ini flag CentroidTriangulation=y as mentioned above, it should prevent these types of tris from being generated. With that enabled, n-gons will get triangulated like "slices of pie" from each n-gon edge to a centroid point (when possible).

Also this problem should automatically get reduced with an increased density of polygons. That's because when n-gons are larger and span a larger area of a surface the degree of non-planarity is also increased. As n-gons get denser they occupy a smaller region of a curved surface which naturally acts more and more like a plane instead of a curve.

So there are a few different things I can try to prevent this. First is if it's a new problem showing up particularly with fillets done in v5 I can probably tune the accuracy of that up. I have a few other ideas to experiment with as well.

Thanks, - Michael

I Am getting the same artifacts from Rom's model when I get close. So I made my own and I am not getting them I uploaded the 3dm file and the blender file.

>>>Hi rom, so it's not that the skinny tris are reversed exactly, it's that the n-gon that they are carved off of is non planar enough that they are ending up pivoted quite a bit.

This is precisely what I'm trying to describe (maybe a bit awkwardly - due to the language barrier :) from the first post. If the exporter generates thin faces rotated approx 70-90 degrees to the surroundings (yep, see skinny_pivot1.png) - it will look cr@ppy virtually in any
DCC\Renderer (BTW in Max I use Vray (Vantage) - I declared it earlier, the model was created in vanilla MOI v5, but I think v4's Exporter would generate the same faulty topology)
I just humbly suggest that mesh exporters should to pay closer attention to the seams between sub-surfaces (seams between fillet and cylinders in my example). IDK, Maybe dedicated (visible or invisible in UI) vertex weld radius, aspect ratio, angle between faces settings.
Regards,

Hi rom, has this only happened specifically on fillets created in MoI v5 ?

Do you have any other examples aside from v5 generated fillets?

- Michael

I think its rather common decease in any NURBS mesh exporter, not just v5.
I'll try to share additional examples later, but its easily reproducible if one doesn't try to hide by injecting higher poly count.
Thank you for attention

Hi rom, it looks like it might be more of a problem with fillets made in v5 where there is an unexpectedly large gap between the fillet surface and the cylinder surface.

So it may be fillets that need fixing up more than or in addition to the mesh exporter - I'm investigating it.

However as mentioned above if you set CentroidTriangulation=y inside moi.ini it should fix the mesh export for now, can you confirm that?

Sorry I didn't understand what you wrote originally!

Thanks,
- Michael

after ini edit it looks way better, THANK YOU so much!
lets hope your investigation will deliver even more refined results

OK here is another example default fbx export (MOI5, ini edit ON, hope it'd help in exporter polishing
numerous artifacts (long thin triangles fail to maintain the general fillet curvature)
Regards,

Hi Michael,
In 2016 in the old thread about centroid triangulation you wrote:

@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.

So i would like to remind you for V5 :-)

@rom

Looks again like a vertex normal data problem on your side. That's the .FBX provided directly rendered in Houdini.
I know Max have hundred of options in the .FBX import dialog, there must be something about recomputing vertex normal's, or creating Smoothing Groups that need to be disabled.
The goal is the read vertex normals MoI's created.

Previously you said : `MOI's export preview is rather schematic and hides the bare truth`.

Actually that's not true, the mesh MoI display at export time should look exactly the same in your DCC viewport. If you see a difference, like dark shading area or ugly sharp triangle like you post above using the 'generic' display mode (opengl/directx/Vulkan), it's a good indication that something is lost in the import process, or something get mess-up after the import (vertex merging, attempt to reduce/edit the geometry, normals re-computing using an average method etc).

Hi rom,

re:
> (long thin triangles fail to maintain the general fillet curvature)

Low poly artifacts like that will just generally be what you can expect if you are trying to restrict polygon count.

The main way to make polygons adapt to the fillet's curvature better is to move the slider towards the right so it will have more subdivisions in curved areas.

I don't really understand why you refuse to do that?

For this case put in angle = 8 and divide larger than = 4 and that will make a much higher quality mesh for rendering at just 25k polygons for the whole object.

The defaults are generating just 3k polygons for the entire object, it's just not enough density for rendering quality on something that has tightly curved fillets.

If you want a higher quality result for the default, you can set Angle=6 in moi.ini , that should change what is used for the default angle.

- Michael

Hello Michael,

I'm really hope I'm not wasting too much from you time. I'm rebuilding 'my own' centroid triangulation, and I'm wondering what's is the rule used to excluded large ngones form that process. MoI "centroid" doesn't do that horrible cap. Do you just skip it if ngones to process contains too many points ? I can also see that concave ngones can't be triangulate that way, are you exlcuding those one from the 'process' ?

Not super important, I'm doing 'stuff' very far from my comfort zone, but I'm kinda curious tho. !

Hi PaQ, there isn't a limit on number of points but it does a test that the centroid triangulation won't make a mess.

That happens in UV space and it's pretty simple. For every edge of the n-gon, make a triangle out of the centroid point and the edge points and calculate the signed area of the triangle. If the area is negative it means that triangle is reversed in orientation so don't do a centroid triangulation on that n-gon.

Signed area of a 2D triangle goes like this:

With 2D points K, L, M

XLK =   L.x - K.x;
XMK = M.x - K.x;
YLK =   L.y - K.y;
YMK = M.y - K.y;

signed_area = 0.5 * (XLK*YMK - XMK*YLK);

The sign will be negative if the triangle vertices are in clockwise order, positive if counter-clockwise.

ref:
A programmer's geometry pg. 62
Adrian Bowyer, John Woodwark
Page 62, chapter 4.1 "Area of a triangle"

You can leave out the * 0.5 in this case since it doesn't actually need the area, it just needs to know if it's positive or negative.

- Michael

Oh nice, thanks for the explanation, I will try to apply that logic !

@PaQ Hereby is fragment of MOI's (sic!) preview. Rotated triangles almost 90 degree are scattered everywhere. I can't blame my Max's importer here - Its a classic GIGO case.
The default fbx export settings delivers pretty high poly count, so we cant say its because of being low poly.

Hello,

Sorry it's hard to understand what area/model you are pointing with that last screenshot. Since using centroid triangulation I can't find any of those 90 degree issue.

If I look at the previous issue in MoI, here's what I have using the default settings :



I can see a small issue (red area), but nothing like those black triangles and other ugly shading variation like you show in 3dsmax.




As Michael suggest, giving it a bit more room (lower angle, divide larger than) produce much better render mesh. Even if you can consider the triangulation not 'optimal', I can't find any glitches or visual imperfection looking at the shading view alone. This is exactly how my model look's like in my DCC, Moi doesn't hide or enhance anything.

@Michael Gibson

>>Low poly artifacts like that will just generally be what you can expect if you are trying to restrict polygon count.
The main way to make polygons adapt to the fillet's curvature better is to move the slider towards the right so it will have more subdivisions in curved areas.
I don't really understand why you refuse to do that?

Because I'm from Archviz field and usually my projects (hotels, malls, city blocks etc) contain **tens of thousands** entourage objects (which I'd like to make in MOI). even using proxies and forest packs we, Archviz monkeys, have to keep poly count discipline.
I attach a screenshot of a typical mesh from some good model maker. Notice 3-5 segments for a fillet, 16-24 segs for cylinder - no more. 24 segments for a fillet (your and PaQ's sujeestions) is not an option in my case,
https://storage.de.cloud.ovh.net/v1/AUTH_cfac7191c3a34a1e9648a2af88284d53/VP_Download_Mirror/catalogs/3D_MALL_EQUIPMENT_catalog.pdf