See this thread on transforming 3D positions to 2D coordinates: https://groups.google.com/forum/#!searchin/cesium-dev/scenetransforms%7Csort:date/cesium-dev/pR7WKlzhZ8w/zX4-6IrLBwAJ
And the reverse can be done with scene.pickPosition.
Would definitely be curious to see the result! Is this part of a university project?