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triangulation
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triangulation // Work in Progress
Post by MikeJoel // Sep 9, 2008, 10:32am
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MikeJoel
Total Posts: 266
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If I allow TS to triangulate a model with holes I get something like this.
(This is a model I did a while back of an audio tape)
Is this "wrong" or is it ok? It still UVs ok.
Mike |
Post by Weevil // Sep 9, 2008, 10:38am
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Weevil
Total Posts: 534
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It does that because it's triangulating EVERY vertice you've got on that face, it's nasty and it's better to do it manually but eveything UV's right |
Post by MikeJoel // Sep 9, 2008, 10:44am
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MikeJoel
Total Posts: 266
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Thank you.
I think I may not have expressed myself correctly :)
To convert the model it has to be triangulated (to my understanding all vertices).
The way it is triangulating, while I dislike the way it look in wireframe it still renders fine. What would be the purpose of triangulating by hand (also compared to the fact that I would probably take a week to do the complete model). This probably has to do with a previous question I had on "clean" modeling.
If the model renders correctly what is the use in spending all the time trying to triangulate by hand?
Thanks
Mike |
Post by kena // Sep 9, 2008, 11:06am
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kena
Total Posts: 2321
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It looks good to me. If you REALLY want to clean it up - quad divide the face a couple of times before triangulating and see if it looks "cleaner". However what you have there should be ok for export. |
Post by TomG // Sep 9, 2008, 11:37am
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TomG
Total Posts: 3397
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Will it work? Depends on the render engine it is going to. I call this "messy" triangulation. The long thin triangles, all connecting to the same vertex, can cause many issues. Usually this happens with the normals, and shows up as specular highlights reflecting differently, so that each triangle shows up as being a little bit different in the real-time engine (or even final render). Most forms of auto triangulation do this, and it's not pleasant ;)
These effects can be seen in tS, as well as in other applications. Quite what effects are seen depends on the render engine in question, some may be fine, some may not.
The object is also very hard to work with once in this state.
So I like to manually triangulate in these cases, to remove long thin triangles, and to remove all faces connecting up to a single vertex. I join between symmetrical elements (eg you could connect vertices from the right center hole in the cassette to the matching vertex on the left center hole, giving long thin quads all lined up, rather than long thin triangles all spawning from the same vertex).
For holes where this is not possible I usually do what I think of as a "cascading star" - I take 3 or 4 vertices and connect then out to a new vertex drawn on the surface, ensuring the triangles are nice and "fat" if I can. I go around the hole doing this, ending up with a new ring of vertices, only now significantly less than the inner ring. I repeat the process with this new ring if need be. Eventually I end up with a simple enough ring that I can join the vertices out to other vertices on the outside of the face.
It's a way of taking 4 vertices and making them into 1, and repeating, until I get a simple shape that can hook up to the outside faces without lots of long thin triangles heading to the same vertex.
It is quite a time consuming process, but does remove render artefacts entirely I have found.
You could do something less complex, maybe surround each round hole with a square, and then just connect up each quarter of the hole to the vertex of the square. Or maybe use a hexagon if you find some of the triangles are still somewhat thin.
Your mileage will vary, it does all depend on the receiving application, and what you want to do when you get there. If you want to render it in a specific game engine, and you test and it works, well don't bother putting in more work :)
If you want to load it into another 3D app and render, and it works, same thing. If you want to sell it to people using that other 3D app, well, they may want to work with the object, modify it, bevel faces, etc, and this dense triangulation would be a problem there. You may want to export to several engines, or don't know which one the object will be used in if you are selling it, so the time spent is then worthwhile to avoid customers coming with complaints.
Note that the Quadrify tool does a much better job of triangulating than the old Triangulate tool or Split Faces does. Also note that you can sometimes compromise, do a bit of manual editing, add in some extra edges or face loops, and then try the Quadrify tool - the extra edges and vertices give it more places that are nearby, so triangles will be less long, and there is more chance of a "suitable" vertex being chosen rather than all points heading off to just one.
HTH!
Tom |
Post by TomG // Sep 9, 2008, 12:05pm
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TomG
Total Posts: 3397
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Here's an example of how I triangulated an object, destined for multiple possible render engines. It rendered fine in tS no matter what I did, and Quadrify wasn't too bad, but I still decided to tackle it myself to avoid long thins :)
I didn't quite do the "cascading star" approach here, but you can see the principle I like to use of linking vertices up to a newly added vertex and so having a series of simplifications as we move outward from the original hole.
Oh, for faces that are not holes btw, the Tip tool provides an excellent solution, and avoids lots of criss-crossing triangulation from other approaches (these holes dont go all the way through and you can see the tip tool used there - I just move the vertex back flush to face, a tip with no height).
If you know where it is going, then you can test and see if this is something you just don't need to worry about, by doing an export with auto triangulation and seeing how it works. Only tackle this if you see problems, or if you don't know the render engine and want to minimize the risk of users having problems.
HTH!
Tom |
Post by MikeJoel // Sep 9, 2008, 2:51pm
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MikeJoel
Total Posts: 266
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Thank you, I was going to ask about a tutorial on triangulation :D
So you basically build a tree structure out so that the thin triangles have the smallest effect possible (there still there but they stay local to their area)?
I guess this would also make you want to use as few faces as possible on when using a cylinder to cut :D
Thanks
Mike |
Post by TomG // Sep 9, 2008, 4:10pm
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TomG
Total Posts: 3397
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It's not just the thickness of the triangle, but the length too. Short thin triangles are ok. But the longer they become, and the more of them that start out from the same vertex, the more of a potential render problem there is.
So the aim is to have less long thin triangles and not so many connecting to the same vertex. Leaving them thin, but not long, is ok :) And of course sometimes they don't cause a problem eithe way, so do be sure that it is worth the effort before diving in to it!
HTH!
Tom |
Post by RAYMAN // Sep 9, 2008, 8:52pm
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RAYMAN
Total Posts: 1496
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If you want some insight how Rich Hurrey from Pixar makes holes on
curved surfaces then here is some insight I found it while learning
Modo but can be replcated with any software....
http://www.luxology.com/training/video.aspx?id=207&auto=1
What to avoid and what flow is best for making these kind of things...
your not going to run into these longish structures that way !
Peter |
Post by RAYMAN // Sep 10, 2008, 9:12am
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RAYMAN
Total Posts: 1496
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You get an insight on how a modeler from Pixar
tackles these problems and what to avoid and no comment at all ?:o
That is at least some very clean modelling !;)
(long video with long intro but worth it I think !)
Peter |
Post by MikeJoel // Sep 10, 2008, 11:56am
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MikeJoel
Total Posts: 266
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Thanks.
I'm downloading the video (slow dialup, 28.8, slow of the slow).
Should only take 10 hours :D
Again everyone for the pointers. I'm going to go try it.
Mike |
Post by MikeJoel // Sep 10, 2008, 6:11pm
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MikeJoel
Total Posts: 266
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Great video (a little boring until he actually does something) but great.
To bad it doesn't work in TS? I take a plane and divide it up. Then do like he did pulling vertices to the cirlce points. But with the place it seems to leave a back to it?
But the front's subdivision is great!
Mike |
Post by RAYMAN // Sep 10, 2008, 6:18pm
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RAYMAN
Total Posts: 1496
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To bad it doesn't work in TS? I take a plane and divide it up. Then do like he did pulling vertices to the cirlce points. But with the place it seems to leave a back to it?
But the front's subdivision is great!
Mike
I do think it is possible from within Truespace !
maybe not that fast but with some effort doable ! |
Post by MikeJoel // Sep 10, 2008, 6:32pm
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MikeJoel
Total Posts: 266
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It seems the plane has a front and back. I tried it with a block and it wont work either. Then I realized. The problem is the unless they are connected somehow then TS doesn't see it as a hole but just an n-gone. |
Post by MikeJoel // Sep 14, 2008, 4:45am
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MikeJoel
Total Posts: 266
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Hmm. I put this in Milkshape and at first it seems nice and smooth.
Then I loaded it again and it was faceted. My triangles wrong? Or is it just milkshape?
Mike
P.S. In blender it looks fine |
Post by Breech Block // Sep 27, 2008, 12:03pm
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Breech Block
Total Posts: 844
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You get an insight on how a modeler from Pixar
tackles these problems and what to avoid and no comment at all ?:o
That is at least some very clean modelling !;)
(long video with long intro but worth it I think !)
Peter
Rayman, I have just watched the video you provided a link for and found the whole thing to be really fascinating. Do you have links to any more videos like this.
Apologies to you Mike if this is hijacking your thread. |
Post by RAYMAN // Sep 27, 2008, 11:30pm
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RAYMAN
Total Posts: 1496
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No sorry !
but if I do get around them I will post the links !
Peter |
Post by JimB // Sep 28, 2008, 12:53am
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JimB
Total Posts: 341
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Hmm. I put this in Milkshape and at first it seems nice and smooth.
Then I loaded it again and it was faceted. My triangles wrong? Or is it just milkshape?
Mike
P.S. In blender it looks fine
I see nothing wrong with using boolean union and triangulating,there might be the need for a little tidy up afterwards but the texture seems unaffected at least for me.
http://img521.imageshack.us/img521/3541/ptankcz9.th.jpg (http://img521.imageshack.us/my.php?image=ptankcz9.jpg)
Jim |
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