koobas.hobune.stream
Equirectangular or radial texture scaling on a sphere
Hello,
I want to project several equirectangular textures on a sphere (each texture contains only on earth continent kept at its original equirectangular shape, the rest is transparent). I want to scale the sphere so that the continents keep their surface/size and stay at their position without scaling with the sphere. All of this done in a Shader. Projector approaches are excluded as the continent/texture can map behind the frustum depending on it's original size or the sphere size.
I am now struggling with this since some days not being able to find the solution.
My approach is so far to resize the texture UV proportionally to the scaling of the sphere (so that it seems to keep its surface and position) but it does not work properly as it scales in the cartesian plane whereas it should be a scaling in equirectangular or radial coordinate system. And I don't know the maths to do that...
Maybe someone knows the maths to scale in equirectangular or radial coordinate systems ? Maybe I am just complicating things and there is something to do with world coords. I was also thinking to project equirectangular to gnomonic, scale, then re-project to equirectangular but I am pretty sure this is overkill and too approximate.
See the illustration:
