Data transformation

Abstract

From the user’s point of view, one official reference frame of GNSS would be desirable. For several reasons, the reality is far from this idealization: the reference frame of GPS is WGS-84, for GLONASS it is PE-90, and also Galileo with GTRF will have its own reference frame (see Sects. 9.2, 10.2, and 11.2, respectively). Nevertheless, the main property of these reference frames is the same; they are realized by a geocentric Cartesian coordinate system. Therefore, when using GNSS, the coordinates of terrestrial sites are obtained in the respective reference frame. The surveyor is not, usually, interested in coordinates of the terrestrial points referring to a global frame; rather, the results are preferred in a local coordinate frame either as geodetic (i.e., ellipsoidal) coordinates, as plane coordinates, or as vectors combined with other terrestrial data. Since the realization of the GNSS reference frame (WGS-84, PE-90, GTRF) is a geocentric system and the local system usually is not, certain transformations are required. The subsequent sections deal with the transformations most frequently used.