As if it hadn't gotten complex enough for me, he he, now there's also the projection to keep in mind! I'll try to grasp my head around that. Does it mean the way you devised to check the rotation on PS or GIMP won't give accurate results,I mean, as simplified as it is? Because to be honest, unless the results would be VERY different from those you would get by keeping in mind stereographic projection, I think it would be enough for me.

And you don't need to thank me, It's only fair you got something back of all this, after all your suggestions and help and patience to help me understand this whole thing better.