Add constructor and set operations to the Voxelgrid class

I am trying to voxelize pointcloud and a reconstructed mesh. and I want to then add the voxels that already don't exist in the pointcloud from the mesh. But apparently union or intersection is not supported on voxel grids. I tried to get the voxel coordinates do my set operations on the voxel coordinates and then return it to a voxelgrid but then I realised there doesn't seem to be a way to initialize a voxelgrid from a set of voxel coordinates.