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Thread: Polygon edge problem

  1. #1
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    Polygon edge problem

    I do research on the Antikythera Mechanism - an ancient Greek astronomical calculating machine (http://www.antikythera-mechanism.gr). I am creating LW objects from 3D X-rays of the fragments of the Mechanism. I extract a stereo lithographic (STL) file from the X-rays using VGStudio Max software (specialist 3D X-ray viewing software). I then import this into LW using SHM_STL_Importer and project still photos onto the surfaces (after considerable cleaning of the chaotic geometry that the process creates as well as the filling of many holes where the X-rays don't see the visual surfaces.) The results have far surpassed my expectations (after a lot of experimenting), but I have a problem. For each fragment, I get a few random polygons that are outlined with white edges (dotted in some places). I look carefully at these polygons in modeler, but cannot see the reason for this. I have found these edges very hard to eradicate. Any suggestions?
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  2. #2
    It looks to me like you have 2 point polygons that are rendering. In modeler press "w" to bring up the statistics panel in polygon mode and click on the white "+" sign beside where it says 2 Vertices. This will select any 2 point polygons on you model then you can delete them.
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  3. #3
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    Wink Polygon edge problem resolved.

    Many thanks to Nicholas Jordan for solving my problem. For the fragment in question, I found 609 two-point polygons and eliminated them instantly - wonderful! We have 82 fragments of the Antikythera Mechanism, so this has saved me hours of frustration. It's really great that experienced users of LW give their expertise in this way to relative newcomers like myself. Very many thanks!

  4. #4
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    Projection onto mesh problem

    Since I had such success solving my previous problem in creating objects from my 3D X-rays of the Antikythera Mechanism, I hope no-one minds another problem. I am making LW objects from the 3-D X-rays combined with high-quality photos of the surfaces. Having spent more than 2,000 years under water, the fragments of the Antikythera Mechanism are conglomerations of bronze, bronze corrosion products, calcification and sea accretions. This means that their X-ray density is very variable. In some places, the fragments look solid to the eye, but are almost completely transparent to X-rays (since almost all of the original bronze has disappeared). This means that, when I extract an STL file from the X-rays, I often get holes where there should be surface. I overcome this problem by creating thin meshes which I cut to the size of the fragment. I then raise up the points of the mesh to match the surface contour of the fragment. I project exactly the same photo onto this mesh as I do onto the STL surface. This nicely fills the holes in a seamless way and the fragments then look like the originals. Sometimes, however, the photo fails to project properly onto the mesh - see attached picture. Particularly where the mesh is sharply contoured, I get black squares where there should be image. Sometimes I can solve this by smoothing, but often I can't get rid of this failure to project the photo onto the mesh. Any ideas would be much appreciated.
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  5. #5
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    Problem fixed!

    Further to my previous post, I got an instinct that this was probably to do with non-planar polygons. So i went to Multiply>Triple and it solved the problem. This forum inspired me to think that there must be an easy solution - so thanks again!

  6. #6
    Registered User Deadlyforce's Avatar
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    Maybe you can avoid tripling polys. I would strongly recommand that free plugin : Normal Corrector.


    http://www.lwplugindb.com/Plugin.aspx?id=20e5fbf4


  7. #7
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    Quote Originally Posted by tony_free View Post
    Further to my previous post, I got an instinct that this was probably to do with non-planar polygons. So i went to Multiply>Triple and it solved the problem. This forum inspired me to think that there must be an easy solution - so thanks again!
    "Shift I" is also a good idea if you have just cleaned up 2 point polys. Those holes might also be doubled; like two polys occupying the same points as it were and both facing the wrong way.

  8. #8
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    Interesting project, btw

  9. #9
    Quote Originally Posted by tony_free View Post
    Many thanks to Nicholas Jordan for solving my problem. For the fragment in question, I found 609 two-point polygons and eliminated them instantly - wonderful! We have 82 fragments of the Antikythera Mechanism, so this has saved me hours of frustration. It's really great that experienced users of LW give their expertise in this way to relative newcomers like myself. Very many thanks!
    Glad I could help.
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  10. #10
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    Wink Thanks for the tip on fixing non-planar polys

    Quote Originally Posted by Deadlyforce View Post
    Maybe you can avoid tripling polys. I would strongly recommand that free plugin : Normal Corrector.


    http://www.lwplugindb.com/Plugin.aspx?id=20e5fbf4

    Thanks very much for the tip on fixing non-planar polys. NormalCorrector partially worked, but not totally. I then thought that I only need to triple the problem areas. So now I use NormalCorrector + triple polys in remaining problem areas.

  11. #11
    MergeTrigons_X to re-merge co-planar Tris.
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  12. #12
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    maybe flipped polys? zoom inside the object, select and hit f to flip, or double side the polys in your surface editor

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