puzzle: where is the inverted normal?

Discussion in 'Design and Modeling' started by frankbuss, May 2, 2009.

  1. frankbuss
    frankbuss New Member
    The model test2.stl is part of a bigger project and Shapeways says that it has inverted normals, but I can't find them. And MiniMagics says "2 Shells". MeshLab wants to delete 2 faces with the remove Non Manifold repair filter. After this I can choose "close holes" and the model works, too, but this doesn't work for more complex models

    I think the two main problems with this model are overlapping polygons and polygons inside the mesh. I can repair it by hand with Blender (test3.stl), but would be nice to have a program which is more clever. The result should be one or more nice polyhedra without anything overlapping or intersecting and without holes. Is there a simple filter in Meshlab which can do this? Some filter crashes with more complex models, so I don't know, if they work. Some filters looks promising, like the "Uniform Mesh Resampling", but it creates small failures in the model and is unusable with finer details for larger models. Any other program, which can fix STL files automaticly, or at very few user interaction?

    I think it would be interesting to enhance MeshLab with some easy to use STL fixing algorithms. My favorite algorithm would be a shrinkwrap algorithm, like more expensive CAD programs can do it when exporting STL: Assuming closed polyhedra (MeshLab can already close holes, so would be no problem to close it before applying this algorithm), it has just to delete anything inside, recalculate normals and the result would be clean non-overlapping meshes. I assume this would fix more than 90% of the problems reported in this forum.
  2. RalphVdB
    RalphVdB Well-Known Member CS Team
    Hi Frank,

    I took the liberty to check your models. Both had 12 overlapping triangles in them.

    You probaly have to rescale them though. When uploading I got the message that one size was under 2 mm.

    Hope this helps you out!



    Attached Files:

  3. RalphVdB
    RalphVdB Well-Known Member CS Team
    Oeps forgot the second one ;).....

    Attached Files:

    Last edited: May 4, 2009
  4. frankbuss
    frankbuss New Member
    Thanks for fixing the parts, but you know the saying: Give a man a fish; you have fed him for today. Teach a man to fish; and you have fed him for a lifetime :)

    I don't plan to print this part, but my support request was, if someone knows how I can fix parts like this, and bigger parts, automaticly by myself, if possible with a cheap or free program.

    Another reason for this posting was the misleading error message by Shapeways. As you wrote, there were overlapping triangles. This would be more helpful as an error message instead of "inverted normals".