Rendering artifactrs for "underground" geometries

Hello,

First of all, thanks for the engine and for its glTF feature.

By default, we do not depth test against terrain when rendering primitives. This is so that billboards, polygons and polylines which are on the surface of the Earth do not get partially buried. If you would like primitives to be obscured when under the earth, you can set the depthTestAgainstTerrain property of centralBody to true. If you’re using the Viewer or CesiumWidget, you can do that with:

viewer.centralBody.depthTestAgainstTerrain = true;

Thank you.