Self-Intersecting faces?

Discussion in 'Design and Modeling' started by BNengineer, Apr 20, 2012.

  1. BNengineer
    BNengineer New Member
    Hi all,

    I'm new to 3d plotting, and after our first little 3d-plot it seems that we have a polygonal issue. After submitting a large number of variation of the same model to the site I'vecome to believe that the problem is probably the self-intersecting faces that are in my model. I use 3d studio max as a modeller. Does anybody know a solution in 3d studio max to fix self-intersecting faces?
  2. SGDesigns
    SGDesigns New Member
    Whenever I have issues with my models, I fix it with Rhino, the "CheckMesh" feature tells you exactly whats wrong with the model. I know you wanted a fix using 3d Studio, I use 3ds too, but I find that using Rhino to fix models is a lot faster and easy.
  3. stop4stuff
    stop4stuff Well-Known Member
    A question as I don't understand and sorry if this is a numpty question;
    How is it that a triangle can have a 'self intersecting face'?

  4. SGDesigns
    SGDesigns New Member
    Last edited: Apr 22, 2012
  5. stop4stuff
    stop4stuff Well-Known Member
    Nope, sorry, I still don't get how a triangle (a face) can self intersect - perhaps the terminology is different to what I understand, so please ignore me and carry on as you were.

    --> whoosh... me gone
  6. stonysmith
    stonysmith Well-Known Member Moderator
    It is not that a single face is intersecting itself, but rather that the shell as a whole has faces that intersect each other.

    Here is an extreme example: the red faces are self-intersecting with the green face.

    Several drawing programs have trouble with this kind of geometry. With some programs you can apply a "boolean" operation to resolve some such cases, but the particular case I've shown here is very problematic.

    Meshlab has an operation called "Alpha shape" but I've not succeeded in getting it to work in very many cases. I usually have to add my own extra vertexes to resolve the problem areas. This can be particularly troublesome if such faces are extremely small.
  7. SGDesigns
    SGDesigns New Member
    Hi BNengineer, are you getting these self-intersecting faces after you boolean of loft? Im not sure if your 3d Studio has ProBoolean, I find this better then the old boolean. If not, then this link might be helpful.

    Last edited: Apr 23, 2012
  8. BNengineer
    BNengineer New Member
    first of a picture of the problem:

    What happens is that the geometry as to be 3d-plotted will come out fine. The white polygons however, which are on all sides of the design are supposed to be grey 'concrete' like the rest.

    @ stop4stuff: I do not know. I think it is some face going through a number of other faces. the face itself however i cannot seem to select in order to delete.

    @ stonysmith
    regretfully my case of selfintersection is not so clear. I do not see the faces in 3d studio max that according to netfabb intersect.

    @ SG Designs, I've downloaded a eval copy of Rhino, but when i rendered my model in Rhino my model was pretty messed up with regard to normals, even after checking and fixing my mesh.

    I am getting the self-intersecting face after I export the model from Revit. I've used .dwg and .fbx exports from Revit, Both give the same issues with the polygons. So I don't get a boolean of loft, I get meshes from Revit.

    currently I am uploading a model in which I have tried to boolean one of the problems away...

    Thanks so much for the assistance of y'all!
  9. stop4stuff
    stop4stuff Well-Known Member
    Thanks for the explaination Stony. The difference in teminology got me confuddled.


    It looks like your model is made up of shells that share geometry, correct? If so, slightly overlapping the shells may fix the issue.

    I hope this image shows what I mean.



  10. BNengineer
    BNengineer New Member

    The geometry is indeed made up of meshes, or shells. I've tried overlapping, by moving the different polygons, but this only gave me a bigger white face. Boolean seemed to work, but when i resolved one issue, another came up.

    A collegue of mine did the ultimate in fixing 3d models (SAT-file -> Inventor -> commando Shrinkwrap -> IPT-file, 3ds Max, VRML-file) and even this file still cause some (but a lot less) of these white problems.

    I am now trying to boolean these problems out of existence...

    This is really a hairpulling issue
  11. stonysmith
    stonysmith Well-Known Member Moderator
    One small thing to check:

    Open the WRL file in notepad or some other text editor, and ensure that ALL of the TRANSPARENCY values are set to zero, and/or just remove them completely.

    The Shapeways renderer has troubles with transparent values.
  12. stop4stuff
    stop4stuff Well-Known Member
    Now this is an issue I understand and have a method for fixing.

    Forget the colour for now.

    Build the model step by step, add a few shells at a time.

    Between each step save or convert the file to an stl. You may need MeshLab(ML) or Accutrans3D(AT) to 'flatten' (in ML) or 'merge' (in AT) the shells if your software doesn't. The next stage is to upload your the interim model to NetFabb Cloud Service - you'll need to enter an email address and you will get two emails, the first letting you know the model is being processed, the second letting you know processing has finished or failed. The only times I've had it fail was when it couldn't cope with the amount of rings in a chain maille models.

    The cloud service makes a neat job of slicing shells at their intersections and then joining the parts as one mesh. Once the model's shell is as a single complete shell, then colour.

    There is one downside the cloud service can come up some unexpected results with shells sharing the same geometry, overlapping shells slightly is required.

    I haven't got NetFabb Pro, but I understand the software does the same kind of merge operations if you have access to that.

    If you're really stuck for a cure, I use some old skool software called Imagine for my creations mostly by directly editing the mesh and would gladly help you out.

  13. BNengineer
    BNengineer New Member
    @stonysmith, checked the .wrl in the notepad, regretfully, none of my faces have transparency.

    So I tried @stop4stuff (Paul's) solution. This seems to fix the meshes, but at the same time it creates issues with the vertex normals.

    So i've taken a blunt object to the model and basically removed the erroneous parts from the inventor model and replaced them with boxes in the right colour. The outside is now perfect, the errors are now on the inside of the model.

    I'd like to thank you all for sharing thoughts and methods on how to fix my issues. I hope the inside will not become an issue and that a perfect outside is enough.