Face Switching Over LoD with SketchUp

[Alexei Lutrova]

I have created in SketchUp 7 a mesh with four different models for each level of detail and an independent physics model. In SketchUp they have all been textured using the same set of textures.However, when I upload the models into a single mesh, the final product swaps textures over the different levels of detail. For example, the texture applied to the base face on the highest LoD will instead apply itself to the trim face on medium LoD.

I have tried to record which faces are switched where in the mesh and compensate in SketchUp by flipping textures around. For the medium LoD I would apply in SketchUp the base texture to the trim and so on, hoping they would be switched to the correct faces in SL.

After screwing around with this for awhile, however, I've had no luck solving it. I can't find a pattern in how the textures switch around or determine whether this is a SL or SketchUp problem.

My question is this: Has anyone else experienced or could explain this problem with SketchUp? OR Can anyone suggest a different program (preferably Blender or Autodesk) that could provide the simplest workaround?

Thanks.

[Fluffy Sharkfin]

I'm not a SketchUp user myself so can't really offer any application-specific advice, but the issue you're describing sounds exactly like the problems that occur when not all the materials used on the model are present for each LOD.

It may be worth double-checking to ensure you've included all the materials for your model in every version, and that you haven't missed any faces when applying textures (thereby introducing an extra 'default' texture to one of the models that doesn't appear on the other three).  Even if the faces on which a material appears no longer exist in a lower LOD version, all materials used on a model must be present in each LOD, otherwise the result is exactly the same as the problem you described. If necessary, just add a single hidden polygon for each missing material and apply the materials to those.

[Alexei Lutrova]

SketchUp gives me a report of the number of materials and textures I export every time I export to Collada. Those numbers are all the same and I'm pretty confident in my model work to say all faces are textured. Still, I tried sticking in a default polygon on each model and still ran up against the same problem. Maybe as I export each model SketchUp records the textures on each as unique entities not tied in to a central library.

For anyone who uses SketchUp to model in your workflow, what do you export to before bringing it into Second Life?

[Drongle McMahon]

It would help to know what viewer (version) you are using, as there are some differences among fairly recent versions. In general, the materials are associated by name in the latest ll viewers (bata and release). You should get an error message if the same names are not present in each. However, the name is not compulsory in Collada and your expotre might omit them (look for '<xxx material= "....." ...>', where xxx is 'triangles', 'polygons' or 'polylist' - the name is in the quotes). It may be in that case, and was always in the older viewers, that the names are ignored. If so, the materials are applied in the order of appearance of the <triangles...>  etc sections. If the corresponding sections do not appear in the same order in the different LOD files, then they will not get the intended materials. You can rearrange them by hand in a text editor.Playing with tyhis might solve your problem*.

The material name is actually an indirect link to the definition of the material, and that definition may point bto the texture if you upload textures with your model. Differences in these links couid also cause the mixing up uf the textures applied at different LODs (although I have never seen this with Blender). So without inspecting the Collada file, it is difficult to identify the problem..

*If you have multiple objects, these will each become a <geometry>...</geometry> section, and it is the ordering of the <triangles> etc sections within each of those that matters. The ordering of the <geometry> sections determines which meshes in the lower LODs belong to which meshes at the high LOD.