Ups! Something messed up my post :)

Here is the top part again:

Often the problem is that the geometry center of a prop is shifted (the center of the OBJ is not at coordinate (0, 0, 0)). You don't always notice this because the prop has been moved to the center of the image with the dials.

This can lead to problems when processing such props further. Among other things it can cause the prop to rotate around its parent in a strange way.

The following small Python script based on "Numpy" remedies this. Here is the core:

---