Questioning the Need of Regional Reference Frames

Abstract

Regional Reference Frames are being proposed, established and adopted under the assumption time independent coordinates are better suited for geo-referencing locations than time dependent coordinates when practical purposes are concerned. The RRF (Regional Reference Frame) tries to respond to the request of maintaining wide areas like Europe, North America, South America or Africa, under fixed coordinates along the time, while establishing, at the same time, a modern Geo-Centric System, a TRS (Terrestrial Reference System).

This two objectives are contradictory: if the frame’s coordinates are kept fixed along the time it will no longer realize a TRS; and if the frame is supposed to realize a TRS its coordinates should vary with time.

In order to try to solve this contradiction some RRF, like ETRS89/ETRF89 (European Terrestrial Reference System/European Terrestrial Reference Frame) are not allowed to evolve with time: the actual Frame coordinates are transformed back into the original past epoch. But this “solution” raises more problems than the ones it is supposed to solve, namely the need to know the non-linear displacements suffered by the frame stations between the past epoch and the present time.

According the author’s view point this annoying problem can be avoided if instead of trying to keep the coordinates for some Regions fixed, we use a Global Reference Frame, like ITRF2005 (International Terrestrial Reference Frame 2005) including in the Metadata file of the product, information about the epoch of the coordinates and about the velocities for the area.

Cartography nowadays is Digital Cartography and GIS products are also, obviously, Digital. It won’t therefore pose a problem to transform the Reference System of this kind of Geographical Information products into whatever Reference System is, for the moment, needed.