Full Version: MOI mesh export issue

Show messages:  1-14  15-34  35-49

>>>Ok, but I hope you understand now that there is no difference in render quality from doing this.

You hope in vain :)
This is DEFAULT obj from MOI with some carpaint and hdri. I'm afraid I DO see problems in renders, not matte viewport screenshots.
Can't you see how bad those perpendicular triangles are?

Image Attachments:
default-obj.png 

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and this is DEFAULT obj from plasticity without perpendicular triangles.
I don't know how else to demonstrate they are bad and this issue need to be addressed

Image Attachments:
defaul_plasticity.png 

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Ngoned default obj from MOI. 1000 tris for one fillet

Image Attachments:
moi-ngon-default.jpg  ngon2.png 

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I use blender/cycles regularly. I build in moi and send the files over to blender. I'm attaching your test model. I gave it a metal material and lit it with a hdri. the export as a mesh is default.

Image Attachments:
test.jpg 

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Hi rom, what happens if you edit moi.ini (Options > General > "Edit .ini file" button) and set CentroidTriangulation=y then export with Output: Quads & Triangles, does that get rid of the offending triangles?

Can you describe a bit more about how you are doing the import, like which file format you are using and are you doing any editing of the model after the import?

- Michael

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Actually rom was right about those micro triangles render problem, I never notice it because those "glitches" are really limited when using Ngones export tho. (It might depend of the render engine or the way internal triangulation is respected ?).

Using CentroidTriangulation=y completely fix the problem here, less pleasant topo (visually) but perfect triangulated render mesh.


centroid off vs centroid on.

Image Attachments:
Centroid.JPG 

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However the centroid triangulation option doesn't seems to help when using ngones export (.FBX). It looks like the internal triangulation (middle picture) can still produce this little nasty triangles.
Here's a first fix (Houdini) to 'correctly' triangulate those ngones. However I have to admit I have no clue what a 'centroid triangulation' is ... So I used the uv's as geometry position, triangulate it using a special "avoid small angle" in Houdini, and I restore the geometry position (while keeping vertex normals safe).

Attachments:
CadTriFix.hiplc

Image Attachments:
CadTriFix.JPG 

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@Michael everything is default really (both export and import) - you could post your default obj mesh and I will show you. Or, even better: in C4D assign metallic material, get closer and to the fillet and play with light direction. IDK how one could expect good results with such a problematic topology.
I'll try the the .ini trick tomorrow..
@PaQ at last Haleluya, thank you for confirming!
With Ngons situation is really bad (post 18), with triangulation - better (p#15)
@val2 you are fine because of the distance and maybe higher poly count, get closer to the fillet area, rotate the light and see what those triangles do.

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Hey Rom, well I never notice that problem (in such extreme way) using Ngones with Houdini + Karma/3Delgiht/Mantra. So chances are it's also a matter of file format + DCC/Render Engine.
(.FBX is probably better to use to deal with Ngones ?). But you are right that using MoI tris export without that centroid (.ini) option "on" produce very nasty connections that result into odd reflection.

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>>>So chances are it's also a matter of file format + DCC/Render Engine.
(.FBX is probably better to use to deal with Ngones ?)

Bad mesh is bad in any DCC. MOI's export preview is rather schematic and hides the bare truth :)
On attached pic: The default triangulated fbx inside Sketchup without any fancy metallic shader.
You know where I see TONS of those ugly fillets? On furniture manufacturers sites like Vondom, Kettal, B&B etc.. They design their master pieces in NURBS programs like Rhino and then translate models with defaults settings to FBX\OBJ\3DS - the results are awful almost on any fillet.
I really hope Michael could find some elegant solution..

Image Attachments:
su.png 

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Hi rom, when you export with n-gons, there aren't any triangles stored in the file. The receiving application will generate its own triangulation of the n-gon, or with FBX it's possible to use triangulation from the FBX library code which is what tends to make FBX have more uniform behavior.

I wonder if your render engine and current settings are particularly sensitive to skinny triangles.

Does your renderer use raytraced shadows? What happens if you turn that off, do the darkest spots go away?

- Michael

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I know nothing about Sketchup, but this example here looks like "you" simply f**** up the baked vertex normal.

While I do agree about the issue pointed previously (that again can be fixed using the centroid .ini option), what you call 'bad topology' is irrelevant if you handle the baked vertex normals correctly, meaning, don't touch it, don't discard it, don't post modify the topology unless you know what you are doing.

Also it would be more productive if you give a little more info about the DCC/Render engine you are targeting. I did created tons of large rendering (8-20k) using mesh coming from MoI without much issues, at least no more that all the crap you can get with 'traditional' modelling. (usually coming from mistakes not really visible when working in the viewport, but get revealed at rendertime).

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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

Image Attachments:
CentoidTriangluationRender.JPG  NonCentoidTriangluation.JPG  NonCentoidTriangluationRender.JPG 

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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

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

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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

Image Attachments:
skinny_pivot1.png  skinny_pivot2.png 

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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.

Attachments:
test.3dm
test.blend

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>>>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,

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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

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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

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