not sure what if flattened sphere was deformed additionally. A simple quad does not allow to deform and therefor you cannot align it properly to any nonflat ground, be it a terrain or not. Well it works well when the quad is very small comapred to the terrain, at least smaller than one terrain grid tile.
For towel mesh shadows you should use a mesh wth several segments, so you can aligh the vertices in realtime to the heights of the underlying terrain locations.
For towel mesh shadows you should use a mesh wth several segments, so you can aligh the vertices in realtime to the heights of the underlying terrain locations.