Recommendations on drawing a square over the poles?

I’m using a RectanglePrimitive to draw an arbitrary image in a square over points on the globe. Near the equator the rectangle is square enough and looks fine. When I place it near the poles, it becomes more of a triangle due to the distortion. This appears to be because the rectangle is defined by two points in latitude/longitude. Is there a way to keep a square shape to a rectangle when placed near a pole? Or is there a different primitive that might accomplish this? I like that the normal RectanglePrimitive bends with the curvature of the earth, just not that it narrows with increases/decreases to latitude.

Yes, the RectanglePrimitive follows the lat/lon lines.
Instead, you can try using a Polygon. This would allow you to define the 4 corner points individually.

Here’s a Sandcastle example of how to use a Polygon: http://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Polygons.html

Thanks, I’ll try that. My initial attempt looks like it will probably work for what I want to do.