The singularities are a single point, but in practice the artifacts are visible over a large area near the pole. I'm honestly not sure why you're defending simple cylindrical projections--they have obvious inadequacies when compared to cube maps, as the mapping from sphere to cube map is well-defined everywhere.t00fri wrote:Correct, but on the other hand, the pole singularities are confined to the environments of 1 point each! The maps of the many edge and corner singularities are spreading over many regions of the sphere where we usually want to render more concise information than at the poles...
t00fri wrote:Could you please indicate whether you can see here any kind of 'pinch' problem? This display is just the result from my RGBA base+spec tiles obtained with my new txtools, together with my normalmap tiles from the nmtools. This would clearly be MUCH worse in case of a "one piece" cylindrical texture. "Pole-optimized" VT's really do a good job. I have studied this in great detail in the past.
You've chosen a best-case scenario for the simple cylindrical projection. The near uniform white in Earth's polar region is advantageous for hiding artifacts in that area. With the Moon and most other bodies, we're not so lucky, and I maintain that cube maps would be obviously superior. Also, the area affected by the polar degeneracy shrinks as the size of the texture increases, and there aren't many 64k VTs out there.
And again, there are my original motivations of cloud shadows and cloud textures, where cubemaps have big advantages.
The true test of course is to actually generate and use a cube map in Celestia. I'm confident that it will produce a noticeably superior rendering at the poles, without noticeable artifacts elsewhere.