PV3D DAE Import - Random normals flipped, random scale?

Question

I am developing a PV3D application that imports DAE models exported by Blender's Collada Exporter plugin (1.4). When I build them in Blender, I use exact dimensions (the end-game is to have scale models in PV3D).

Using the same scale of dimensions, some models appear in PV3D extremely tiny, while others are the appropriate size. Many appear with rotations bearing no resemblance to how they were constructed in Blender. Also, I have to flip the normals in Blender in order to get them to display properly in PV3D, and even then, occasional triangles will appear in PV3D with normals still reversed. I can't seem to discern a pattern amongst which models appear tiny. Same goes for the randomly flipping normals - I there doesn't seem to be a pattern to it.

Has anyone had any experience with a problem like this? I can't even think of how to tackle it - the symptoms seem to point to something with the way PV3D handles the import, or how Blender handles the export, and the 3D math is way beyond me.

Answer 1

I finally found the source of the problem a while back, and just remembered I should update this post.

Turns out, the normals weren't being flipped. My models contained relative acute angles and sharp, flat projections (think a low grade ramp). When viewed from certain angles, the z-sorting (which sorts by object center by default) was incorrectly sorting the faces because the acute angles and flat, sharp projections caused the poly's center to be farther away than another poly's center behind it.

The effect was consistent from all my view angles because the camera was restricted to a single, fixed orbit around the models, so the same thing happened in reverse from the other side of the model, making it appear like the normals were flipped.

As for the scale issues - I never figured that out. I moved to Sketchup for my model creation, and that seemed to solve it.

Answer 2

I had a similar problem with the normals, I found that after applying scale/rotation to objdata (I had to make it single user first) the normals were facing in the direction which corresponded to what I was seeing in papervision.

This should fix your scaling issues too.