How to fix triangles with mixed winding order?

Discussion in 'Design and Modeling' started by Rustysworkshop, Jul 23, 2013.

  1. Hello, I just recently attempted to upload my first product to shapeways and received an email back saying there was a problem with my design.

    Advanced Printability Failure Message:
    Triangles with mixed winding order were found. Your model has flipped triangles which cannot be fixed. Make sure your triangle winding is consistent.

    I do not fully understand what this means so don't know how to fix it, so any help would be much appreciated, thanks in advance.

    P.s. I used google sketchup to create my 3d model
     
  2. mkroeker
    mkroeker Well-Known Member
    Winding order refers to the sequence in which the three corners of a triangle are listed in your file - this is important as it is used in the construction of the "surface normal" of your triangle, a vector that points away from the surface of your triangle defining what is "the outside" relative to this face of your model. If not all vertices are sorted in the same order, adjacent patches of your model will disagree in where the solid part of your model is.

    If sketchup itself does not provide a function for fixing "normals" (or possibly "non-manifold meshes"), you can repair your model in either meshlab or netfabb studio basic - both programs are freely available.
     
  3. Thanks for the good explanation and help, I have downloaded both programs. I used meshlab to export my design as an STL and then opened it in netfabb and tried to use the repair function then automatic repair. But the problems are just highlighted in red and still there and I cant seem to fix them.

    Any further advice? thanks
     
  4. It says

    Border edges: 0
    invalid orientation: 1743
    Holes: 0
     
  5. AmLachDesigns
    AmLachDesigns Well-Known Member
    Can you share the .stl?
     
  6. Yes here it is ( I hope)
     

    Attached Files:

  7. please dont mock my lack of 3d modelling skills :)
     
  8. AmLachDesigns
    AmLachDesigns Well-Known Member
    Hi,

    i think you have come up against a problem that many Sketchup users have had. It seems that it is possible to do great things with Sketchup but also that it is possible to create a less than ideal mesh.

    At some point in your designing when you have added new details, instead of the mesh being extended, new detail has been added on top. This gives a non-manifold mesh and also the inverted normals (the winding error).

    I do not think I can fix your mesh, maybe someone who uses Sketchup can either fix it or advise you how to create one that will upload to SW.

    Good luck!
     
  9. Thanks a lot for taking a look at the problem, there was a point where I think I had to add details on top due to limitations of extending the mesh.

    I think I will just try and rebuild it :)
     
  10. AmLachDesigns
    AmLachDesigns Well-Known Member
    Good idea.

    I use Blender but when I change a mesh I use one of 2 ways:
    1. I add or subtract another mesh to/from it using Boolean operations;
    2. I work with the mesh itself by extruding to change the volume or subdividing the mesh to add more detail;

    But whatever you are doing it's a good idea to think of your mesh being a watertight volume with an inside surface and an outside surface. And in this context the Normals all point away from the outside surface.

    Good luck!
     
  11. stonysmith
    stonysmith Well-Known Member Moderator
    Try running this model thru cloud.netfabb.com and see what you get.
     
  12. JACANT
    JACANT Well-Known Member
    As you draw your model use the 'Make Component' command for each piece created, this makes that particular component solid. If you need to draw on top of the model select the new pieces just created, right click and use either the 'intersect faces' with selection or model depending on what you are doing. Or make that selection into another 'Component'. This way, when you have a number of components you can 'Boolean' join them together using the 'Outer shell' command, under Tools. Which will join the solid components together and delete all inside lines not required.
    Do not draw on top of any face that does not need to be there; the software will just create a new face on top of the original face. Then Shapeways software does not know what is inside or out..
    Once you progress with your model keep checking by selecting a face that you know is pointing the correct way and use the right click command 'Orient faces'. If everything is correct it will align all faces to point out. If you see any extra lines on faces delete them. If the face disappears find out why and either do an undo or redraw that line to create the face.
     
  13. bartv
    bartv New Member
    Here, I fixed that for you. What I did is import it in to Blender, enter 'edit mode', select all vertices (A), press CTRL+N to unify the normals, leave edit mode and export as STL.

    Enjoy!

    Bart
     

    Attached Files:

  14. samsonite
    samsonite New Member
    I think shapeway has given you a false warning about the true nature of your problem.

    There are a couple of open edges (small holes) in your model, and it does contain a lot of hidden, interior faces.
    The outside of your model looks ok (consisent normals), so I would guess those interior faces are giving you problems.

    To fix, just fill the small holes and get rid of the interior garbage.


     
    Last edited: Aug 3, 2013
  15. I cant thank you enough bartv that was great and worked perfectly, thanks so much! :D