your terrain is a flat surface, so you only have xz-coordinates, y is constant
you can now transform every vertex by taking the xz-coordinates and map them to a range of 360 degrees and then convert those two angles to the 3d spherical space.
i cannot draw an example right now but in about two days
I'm looking for something very similar to what joao is looking for, I'd love to see your example drawn out. I'm a better visual learner.
