Blender: item saved as DAE is missing parts

[Nescolet]

Hello, I used the latest version of Blener to smooth some rails, before making sure all the piece was seleted. Exported the piece as DAE and when I use latest LL viewer to preview and import I get a piece of rails that has missing sections. I can also see the missing parts of the DAE piece if i open the file with MeshLab. Any idea why could this happen or what I may be doing wrong? Thanks

[Drongle McMahon]

One possibility...

How did you "smooth". Missing pieces can be due to having too many triangles. The exact limits depend on the number of materials used up already, but the uploader starts a new secret material after it gets to 21844 triangles. If you have only one material, that means you can get up to 174752 triangles. Beyond that, the extra triangles are simply omitted from the upload. Of course, that is FAR too many for just about anything, but it is easy to get to that sort of number if you use the subdivision surface modifier to "smooth". That is the way to destroy viewer performance. The preferred way to get smooth surfaces is to use smooth shading (Mesh->Faces->Shade smooth), to gether with the edge split modifier if you need to keep some edges sharp. That will give you much lower LI and much better performance, for equally good appearance with a fraction of the vertex/triangle count. You can achieve something similar by using the Generate normals option in the uploader, but it's not as good and doesn't give you the detailed control you can get with edge split+mark sharp.

[Nescolet]

I applied "smooth" using the Shading: Smooth button under the Object Tools when the whole piece was selected.

After smooth is applied the numbers for the whole piece are the following:

Verts:20542 | Faces: 38048 | Tris:38048 | Objects:34/34

I haven't created any materials because I don't know how to do that yet.

My knowledge of Blender is below basic so far so I will keep your suggestions for when I know how to apply them. Thank you very much for the details Drongle.

[Drongle McMahon]

Not knowing what your rails are, I can't say whether that's too many triangles. Does sound like a lot though. It is certainly more than the 21844. That means you will actually have two materials because the uploader will have started a second one. You might be able to see that inworld by clicking with "Select face" checked in the edit dialog and changing the colour. However, they don't behave quite like two different textures that you specify explicitly, and you might not see it.

Setting the smooth shading the way you did is like using the Mesh->Faces->Shade smooth in edit mode, except that t affects the whole mesh instead of just selected parts. It could cause unwanted effects across sharp edges, but with that triangle count, it's unlikely to be noticeable. It doesn't add any goemetry, so that is ok.

Another common cause of holes is inverted normals. To correct that, you can try going into edit mode, slelecting everything and doing Mesh->Normals->Recalculate outside.

[Nescolet]

I could manage to produce a DAE with no missing pieces if instead of exporting to DAE directly, first I export the piece as OBJ, import this into Blender and then export this as DAE.

Strangely, with a simplified version of the rails this technique proceduced a piece with missing items, but I've found that if I remove all duplicate vertices from every selectable piece before exporting to OBJ, then finally I got a complete DAE.