Buggy texture coordinate generation for raster overlays

[j9liu]

Originally posted on the community forum. The sample data is linked in the initial post.

TL;DR, raster overlays are not being draped correctly over the provided tileset. It was initially observed when using Cesium Polygon Raster Overlay, but I found some weird behavior using Cesium Ion Raster Overlay as well.

I haven't completely pinpointed the source of this bug, but I have a decent guess that it has to do with the texture generation for raster overlays. For instance, take this area of Bing Maps imagery that the tileset will appear over. When it's draped over the tileset, I'd expect the images to line up on the top of the buildings. But it doesn't do that; they only appear green.

Original	Draped on Tileset

So something seems off. Not sure if there's something unique about the tileset, or if we're making an assumption during texture coordinate generation that this case isn't meeting.