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Help - how to avoid double faces in Collada export

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  • T Offline
    TIG Moderator
    last edited by 17 Apr 2019, 09:53

    'Two-sided faces' is an Export 'Option'... make sure it's NOT ticked.
    Also check for proper face orientation by viewing in Monochrome, and reversing any back-faces you can see - [re]applying any materials/textures to the now front-face as necessary...

    TIG

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    • A Offline
      andybot
      last edited by 17 Apr 2019, 14:50

      That's not it. It's a pretty simple model and 2 sided faces is unchecked. I'm curious if people with Blender experience can weigh in here - how do you transfer your models? Like I said, I typically use .obj format, but with obj (and 3ds, and fbx) components come in as unique instances, not linked.

      http://charlottesvillearchitecturalrendering.com/

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      • A Offline
        andybot
        last edited by 18 Apr 2019, 13:24

        So nobody else gets double geometry when they import Collada into Blender?

        http://charlottesvillearchitecturalrendering.com/

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        • J Offline
          juju
          last edited by 19 Apr 2019, 18:15

          @andybot said:

          So nobody else gets double geometry when they import Collada into Blender?

          2 for 1 special?

          Save the Earth, it's the only planet with chocolate.

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          • A Offline
            andybot
            last edited by 19 Apr 2019, 21:39

            🤣
            I dunno, people were saying on another thread that Collada format works great for Blender. Not happening for me.

            http://charlottesvillearchitecturalrendering.com/

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            • T Offline
              TIG Moderator
              last edited by 20 Apr 2019, 12:37

              I don't see 'double geometry' from SketchUp DAE files imported into Blender.
              What I do see is separate meshes created made for each material inside a 'container'.
              And the fronts AND backs of those faces are assigned the same material as the front's - but in a well modeled form you should never be seeing any 'back-faces', so that isn't much of an issue ?
              Because Blender uses meshes, then multiple copies of a SKP's component-instance get treated as separate objects - additionally split by mesh-by-material ??

              Can you take a screenshot of some simple textured faces in a SKP and then exported to DAE-into-Blender - showing what you see... and how it impacts your work...

              TIG

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              • A Offline
                andybot
                last edited by 22 Apr 2019, 16:47

                TIG, Thanks for asking further. Here is a fairly straightforward example of an apartment interior. I've included the original skp file, a Collada export, and the imported Blender file. I'm using SU2016 pro, but I encounter the same problem in SU2018 as well. I've unchecked "double-sided faces" in the export options. Can't think what else I could do differently.


                unit107.zip


                2019-04-22_124449.jpg


                Blender file double faces

                http://charlottesvillearchitecturalrendering.com/

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                • T Offline
                  TIG Moderator
                  last edited by 22 Apr 2019, 21:45

                  I'm no Blender expert.
                  I don't see 'double-faces'...
                  But if I set 'Back-face culling' be 'on', and tweak some other settings, then the 'z-fighting' stops ?
                  Is that your issue??
                  I believe it's Blender's settings, not SketchUp's export-options in play........


                  Capture.PNG

                  TIG

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                  • A Offline
                    andybot
                    last edited by 23 Apr 2019, 13:33

                    So the issue for me is that obj export, also fbx, 3ds, etc. give me correct models without duplicate faces. However, they make each instance of a component unique in the model. Collada seems to be the only format that makes components linked duplicates (meaning that editing one edits all of the instances in the model, like the difference between components and groups in Sketchup.)

                    Yes, I can do workarounds just fine in Blender - what I typically do is "remove doubles" to collapse the duplicate vertices. But this is something I used to have to do with earlier versions of obj export (like in 2012 or so.) I would like Collada to export properly, and now I'm wondering if the checkbox for "Two sided faces" is not actually working correctly.

                    http://charlottesvillearchitecturalrendering.com/

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                    • P Offline
                      Pixero
                      last edited by 23 Apr 2019, 15:35

                      Maybe you could import the collada file into some other 3D app and see how it looks there?

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                      • A Offline
                        andybot
                        last edited by 23 Apr 2019, 16:46

                        @pixero said:

                        Maybe you could import the collada file into some other 3D app and see how it looks there?

                        Yep, I tried that before with FreeCAD, I get double faces there too. I checked again, and same thing.

                        http://charlottesvillearchitecturalrendering.com/

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                        • L Offline
                          Lionelfred
                          last edited by 17 May 2019, 21:51

                          You are not alone. I have terrible problems with this in blender. The result is that in Cycles render (but not in Eevee) you get horrible (I think) z-fighting (where two faces try to be visible at once) and also issues with (I think) flipped normals, which results in the texture of the surface of an object having have some normal textures but some of its triangular faces will show whiteish.

                          This page https://www.katsbits.com/tutorials/blender/sketchup-import-extras.php recognizes the problem and explains possible solutions, but don't hold your breath as they have only very partially solved my problems of double faces.

                          The only way I have found to resolve is quite laborious (how laborious depends on the complexity of the model, of course).

                          • If the problem is z-fighting (you see the texture on the face is greyed out), go round the back of the mesh (I do this in wireframe) and select and delete the face (delete > faces) that is behind. When you go back round the front and toggle out of edit mode, you can see that textures are visible and there's none of that z fighting going on (if that's what it is).

                          • If the problem is flipped normals (the texture is absent on that particular face), then before going round the back, flip the normal on the face at the front (in 2.8 i edit mode, mesh > normals > flip normals). Then go round the back, select the face at the back and delete it.

                          text834.png

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                          • A Offline
                            andybot
                            last edited by 21 May 2019, 13:27

                            I usually use "remove doubles" to collapse the duplicate vertices. It's typically fine, and much quicker than deleting faces individually. The other big problem with Collada is losing smoothing groups. Obj. format export is my typical workflow, the only reason I need Collada is for linked duplicates.

                            http://charlottesvillearchitecturalrendering.com/

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                            • L Offline
                              leva4av
                              last edited by 11 Oct 2022, 20:51

                              This will work.

                              Go to edit mode
                              Select all faces or press A key
                              On top menu select
                              Mesh -> Clean Up -> Merge By distance.

                              This will clear all the double faces.


                              menu options

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                              • A Offline
                                andybot
                                last edited by 13 Oct 2022, 14:59

                                Yes, Blender has gotten rid of "remove doubles" and now relies solely on "merge by distance" now. Never did fix the collada export issues, but doesn't matter as I'm only using Enscape and not rendering in Blender lately.

                                http://charlottesvillearchitecturalrendering.com/

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