Description
Currently GroundPrimitive and GroundPolylinePrimitive set their shadow volume bounds based on approximateTerrainHeights.json, a file full of earth's min and max heights at different longitudes/latitudes. If a user has a custom terrain dataset or uses terrain exaggeration, these approximate heights no longer work and the ground geometry will be clipped.
To fix exaggeration, we could add a height vertex attribute and scale it by terrain exaggeration in the shader. This is a little tricky because there's no more room for attributes for polylines. We could oct encode one of the normals to make space but I don't know if that's a good idea. Another option is to use a uniform or batch table entry with the min and max height, but since the geometry is created in the worker after the batch table / uniforms is created, it doesn't know the values. Also we would need a geodetic surface normal to offset the vert in the right direction. I would prefer baking the exaggeration into the verts if possible. Would need some rearchitecting.
For custom terrain datasets, I don't know... the polyline geometry would have to be rebuilt whenever the terrain underneath it changes.
See #8436 (comment) for an example of polylines breaking.