Background & Issue
High-resolution images of the Earth are readily available [1,2]. If these are reversed horizontally, they can be directly used with the TextureMaptoSphere filter applied to a sphere source.
When mapping the texture to a sphere source, the texture maps very well; however, one of the azimuthal segments contains a reversed and distorted version of the image. The effect can be minimized, but not eliminated, by increasing the theta resolution of the sphere that the texture is applied to. Please see the figures below for varying theta resolutions demonstrating the distortion and mitigation.
Is there a way to overcome this distortion? Using the “prevent seam” option in the TextureMaptoSphere filter prevents a seam but distorts the remainder of the texture by mirroring it.
Alternatively, could there be an off-by-one error in the mapping algorithm? The 720-segment theta resolution case is nearly perfect except for this one segment. If it were eliminated, the fitment would be virtually seamless.
As an aside: is there a reason for the need to horizontally reverse the texture before it is applied? Can/should an obvious GUI control be added to perform this transformation for the texture? Note that modifying the “Transforming” settings permit this type of manipulation, but the correct parameters are non-obvious without a good understanding of coordinate transform techniques.