Tips for OBJ/LWO export?
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 From:  jason
3793.21 In reply to 3793.18 
Hmm. So in cutting off a piece of geometry for you to sample, I've encountered something very strange:

I selected a piece of the original model, deleted the rest, and did a save as. When I went back to open my original, I now have two instances of almost every face in the object. I have to delete them manually as far as I can tell, although I really hope there's a way to collapse/merge them. In fact, I just reopened the piece I trimmed out and it ALSO has two faces where there should be only one. What could possibly cause that to happen?

Here's a screen shot - the clipping you see is the faces on top of one another:



I've also attached the LWO, the 3DM, and a render of the artifacts I'm getting.
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 From:  jason
3793.22 In reply to 3793.21 
Here's the full original model that's now causing me problems if looking at that one is of any help.
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 From:  Michael Gibson
3793.23 In reply to 3793.21 
Hi Jason, my guess is that those rendering artifacts are probably a side effect of the surface duplication - when you get polygons stacked up on top of each other like that it can cause rendering problems with the rendering thinking that some of the polygons are shadowing other ones.

Some areas of the model seem to have even more than just 2 pieces stacked up, I just saw one spot that had 4 stacked up pieces.

It's hard to tell at this point if that duplication was in the original IGES file, or if it was some side effect that happened when attempting to join the surface pieces in the original IGES file together. One way you could tell about this part would be to turn off the automatic joining that happens with IGES importing (that's under Options > Import/Export > IGES options > "Join surfaces on import"). If you have that turned off, when you import the file do you get stacked up pieces or no stacked up pieces?



Also I've attached here a tuned up version of your sample piece, where I have removed the duplicate surfaces and have just single surfaces all joined together. Could you please test exporting and rendering this version and see if your render issues are solved with this version? If so then that would definitely pinpoint that it is the duplicates that are causing the rendering artifacts that you are seeing (most likely in relation to raytrace shadow calculations during the rendering, that's probably why you don't see them in the real-time view since its not doing shadows there), and if that's the case I can then help you to clean up the full model.

- Michael
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 From:  jason
3793.24 In reply to 3793.23 
Nope, still the exact same issue on render. Looks fine in the GL preview, breaks when rendered (albeit in a very slightly different way).
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 From:  jason
3793.25 In reply to 3793.24 
And the bizarre thing about the multiple surfaces issue is that the issue absolutely was not present until I saved the object, closed it, and then re-opened it. I've managed to replicate the problem once or twice, but with absolutely no consistency.

Could there be something wrong with the original IGS file?
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 From:  jason
3793.26 In reply to 3793.25 
Whoa, okay - I figured out the issue with the render artifacts! I swear I tried this very early on in trouble-shooting, but n-gons (well, some of them) were the problem. Simply tripling them worked great.

... but only if I do with triangulation withing Lightwave. If I export from MoI with tris + polys, LW doesn't like it.

I think perhaps the problem is my platform of choice is extremely picky.
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 From:  Michael Gibson
3793.27 In reply to 3793.26 
Hi jason - re: n-gons, I have seen LightWave occasionally have problems with certain kinds of n-gons (they have to be triangulated internally in order to be displayed and if something goes wrong with the triangulation, triangles can kind of leak outside of the boundary), but when that happens it should be seen in the realtime view as well.

That's kind of odd to have an n-gon problem that only shows up at render time and not in the regular realtime display...

Maybe the triangulation step that you're doing removes the vertex normal map, and that has more to do with the change in the rendering than the n-gons?

Can you find the vertex normal map listed in some list of maps? Do you get the same kind of result if you delete that and still have n-gons?


At any rate, I have attached here a version of your file that has the duplicated surfaces removed, if that is of any use.

In some areas of the model there are some very tiny slivery pieces, that's probably one of the things causing joining problems with it.


But it sounds from your reply that you have a solution now that works, is that correct?

- Michael
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 From:  jason
3793.28 In reply to 3793.27 
Yes, I do. I think it was very much a combination of something a little off with the source file and Lightwave being very finicky with n-gons.

Re: the vertex map - it appears to still be applied to my model even after triangulation, because it's very apparent (and messy) if I remove it completely.

Thank you very much for the help.
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 From:  Michael Gibson
3793.29 In reply to 3793.28 
Hi Jason, well that is pretty mysterious as to why triangulating should make such a big difference, especially if exporting from MoI with "Quads & Triangles" instead of n-gons still has the same kind of issue.

But I'm glad you have a method that works anyway.

- Michael
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 From:  Micha
3793.30 In reply to 3793.14 
"When you have a joined object, if you uncheck that "Weld vertices along edges" option, it will still produce a watertight no-crack mesh but the mesh will be clustered into separate non-connected (non-connected in a topological sense, but actually physically touching in location) sets of vertices with one set for each original surface. This will then allow you to use your polygon modeler's mesh processing functions to separate the mesh into individual objects."

I asked for the "mesh like joined" function, because I don't want to get all surfaces of a polysurface unwelded, only selected one. I need the meshes for a mesh unfolder (UV texture coordinates unfolding). Welded mesh parts are treated as one object and each unwelded connection is treated as cut in the mesh.

Attached an example of a seat cushion. I like to get separate side parts, but the mesh should be generated like from a closed polysurface. It's easier to extract NURBS surfaces than mesh parts. If I would disable the MoI weld function than I would get to much cuts in the mesh.

Thanks,
Micha

Visualisation for Designer and Architects | http://www.simulacrum.de
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 From:  Michael Gibson
3793.31 In reply to 3793.30 
Hi Micha, I think you'll need to use a polygon mesh modeler for that kind of "just unweld this one particular surface and not other stuff" kind of level of detail on the mesh processing.

It's difficult to include such very specific detailed functions in MoI's mesher, if it did all kinds of special purpose mesh editing functions like that it will end up getting a really complex UI pretty quickly.

Many polygon mesh editing programs should be able to handle what you need - you probably would want to export from MoI with welding turned off, then select the mesh pieces that you want to keep unwelded, invert the selection and then perform a merge vertices / weld type operation on everything else to weld all the other points together where they had multiple vertices stacked in the same location.


Also maybe I have misunderstood what you are asking for - do you want to actually keep the surfaces as separate unjoined surfaces in MoI but still make them mesh as if they were joined? But if so, that's not really feasible to do, the mesher can't make things work like they are joined without actually knowing which things are joined to one another, so there would have to be an additional full joining calculation done at meshing time in order to know that. That joining calculation can be a time consuming operation, so that's something that you need to do to objects before running them through the mesher, it's not something that the mesher can easily handle in addition to meshing.


> It's easier to extract NURBS surfaces than mesh parts.

This is not usually the case if you're using a mesh modeling program.

- Michael
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 From:  Micha
3793.32 In reply to 3793.31 
Thank you Michael. Right, I will ask the developer of the unfolder for more extraction tools.

Visualisation for Designer and Architects | http://www.simulacrum.de
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