Cave Visibility Under Landscapes

I know what you are expecting but this isn’t about carving a cave into the terrain!

My problem is figuring out the best way to handle visibility of static meshes under the terrain when you want gameplay space on top. Look at the following illustration:


There is no way I know of to completely occlude the cave chunk underground so I have the following problems

  • Aggressive LOD’s- cave rocks and cave itself could go down to one poly. Drawback is I can’t reuse the rock meshes ontop, they have to be a whole new duplicate to use different LOD’s- right? The other problem is the outside world still renders the same.
  • Culling volumes don’t really help because the global one will want to draw meshes the same size as the ones ontop. To the engine there is no difference between ones above or below.
  • Visibility volumes aren’t recommended for large levels and I haven’t been able to get it work either (almost no documentation on these for UE4)
  • Almost all of these solutions require me to have a long entrance tunnel to keep the cave away from the surface of the terrain. Far enough to set an LOD distance that works when you are on top.

Did I miss anything? It seems like the first point is my best solution. Bugs me that the terrain doesn’t act as an occluder.