The "cube coordinate system" described here with a redundant third coordinate is similar to the Bravais-Miller indexes used in crystallography for hexagonal and

The "cube coordinate system" described here with a redundant third coordinate is similar to the Bravais-Miller indexes used in crystallography for hexagonal and trigonal crystals https://en.wikipedia.org/wiki/Miller_index#Case_of_hexagonal_and_rhombohedral_structures https://en.wikipedia.org/wiki/Miller_index#Case_of_hexagonal...