The Geometry of Sampling on Unions of Lattices

In this short note we show two results concerning sampling translation invariant subspaces of $\ltwod$ on unions of lattices. The first result shows that the sampling transform on a union of lattices is a constant times an isometry if and only if the sampling transform on each individual lattice is so. The second result demonstrates that the sampling transforms of two unions of lattices on two bands have orthogonal ranges if and only if correspondingly the sampling transforms of each pair of lattices have orthogonal ranges. We then consider sampling on shifted lattices.