Please use Space Time Coordinates.

The STC system for astronomical coordinates and regions is an IVOA recommendation, and therefore we will all gain through interoperability. This interoperability is not just for technical systems, but also so that concepts learned in one area of VO can be applied in other areas. STC is applicable in many areas: ADQL, footprints, TAP, VOEvent, SIAP, source VOTables, etc. If a WG is intending to make a different representation of coordinate or region, they should explain why they are diverging from a standard already agreed. Further, the new representation should be simply and transparently convertable to STC to promote interoperability.