(2019-12-17, 4:38)Travis Cobbs Wrote: I'm sorry, but I'm still not picturing what you are trying to say, and I still don't see the problem. I'm not saying that you are wrong, I'm just saying that I don't understand. I have attached a file with some extra geometry. The red triangle uses p1, p2, and p3 from the TEXMAP definition. The green square extends that out into an easily seen square around the whole sphere representing P1 from the spec. The blue square represents P2 from the spec as I read the spec. Could you edit the model to move any of the extra geometry to represent what you think the spec says?

Good idea. Consider the two points A and B on the surface of the sphere:

The 'V' components of the UV mapping for these two points is computed by taking their projections onto P2. Let qA be the projection for A onto P2 and qB be the projection of B onto P2:

Let VA be the V component of the UV mapping for A, and VB be the V component of the UV mapping for B where we ignore the scaling factor b:

VA = angle between p1p2 and p1qA

VB = angle between p1p2 and p1qB

As you can see on the second figure, these angles are not euqal. The projection of the texture should thus not portray the two points at the same height. In fact, following the specification to the word will result in this projection: