Spherical shape for use with occlusion culling in [OccluderInstance3D]. [SphereOccluder3D] stores a sphere shape that can be used by the engine's occlusion culling system. See [OccluderInstance3D]'s documentation for instructions on setting up occlusion culling. $DOCS_URL/tutorials/3d/occlusion_culling.html The sphere's radius in 3D units.