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puzzle: where is the inverted normal? [message #4229] Sat, 02 May 2009 18:46 UTC Go to next message
avatar frankbuss  is currently offline frankbuss
Messages: 53
Registered: March 2009
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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.
Re: puzzle: where is the inverted normal? [message #4242 is a reply to message #4229 ] Mon, 04 May 2009 08:20 UTC Go to previous messageGo to next message
avatar RalphVdB  is currently offline RalphVdB
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Registered: July 2008
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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!

Cheers,

Ralph

  • Attachment: test2.stl
    (Size: 2.23KB, Downloaded 265 time(s))


Shapeways International Customer Service Manager
Re: puzzle: where is the inverted normal? [message #4243 is a reply to message #4242 ] Mon, 04 May 2009 08:23 UTC Go to previous messageGo to next message
avatar RalphVdB  is currently offline RalphVdB
Messages: 318
Registered: July 2008
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Oeps forgot the second one Wink.....

  • Attachment: test3.stl
    (Size: 1.84KB, Downloaded 93 time(s))

[Updated on: Mon, 04 May 2009 08:23 UTC]


Shapeways International Customer Service Manager
Re: puzzle: where is the inverted normal? [message #4268 is a reply to message #4243 ] Tue, 05 May 2009 18:34 UTC Go to previous message
avatar frankbuss  is currently offline frankbuss
Messages: 53
Registered: March 2009
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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 Smile

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".

 
   
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