Coordinate format converter

Everything here is the WGS 84 datum; older datums such as NAD 27 or ED 50 sit tens to hundreds of metres away and are not converted. MGRS and UTM share one hand-written Transverse Mercator engine, including the southern Norway (32V) and Svalbard zone exceptions. A decoded MGRS reference names a square, and the tool returns the centre of that square; polar UPS grids (bands A, B, Y, Z) are out of scope.