Query two sphere-based SDFs against each other

[JonathanKuelz]

Hi all,

According to the documentation, CuRobo currently supports collision checks for

cuboids, meshes, nvblox maps, and euclidean signed distance voxel grids

This doesn't seem to cover collision checks for pairs of spherical objects. While there are ways to circumvent this, this seems a bit counter-intuitive at first sight, as

1. CuRobo encourages the use of spheres as object representations in various places, and
2. All the necessary features are probably already implemented, as sphere-sphere SD is the most straightforward of all possible pairings.

So I was wondering: Am I overlooking something? Is this feature missing on purpose? It would be quite useful for things like collision checks between two point clouds.