Indexing the aperture 3 hexagonal discrete global grid

Over the past decade there has been interest in the computer representation of global data based on multi-resolution subdivisions of regular polyhedra. A simple and efficient indexing of the cells of such a subdivision, called A3-coordinates, is introduced. These can be used to encode the 4 · 3n + 2 cells at the nth level of resolution of the octahedral aperture 3 hexagonal discrete global grid using n + 3 digits, each digit from the set {−1, 0, 1}.