How to flatten terrain

[xjindf]

Just like this discussion, but not just 3D title, I hope it can also be realized on the terrain.

How to flat the overlap area between a polygon and a 3D tiles to a specific height?

I was trying to implement a feature that is to flat the overlap area between a polygon and a 3D tiles to a given height but didn’t make it. [Flat a 3D Tiles] Cesium provides the clipping plane feature to trim the 3D Tiles which is very much similar to what I want to implement. The difference is that the clipping discards all the vertex but in my case, I want all the vertexes to be set in the same z value. Therefore, I tried to modify the z value of there discarded fragment in the clipping sh…