Reference frames for GNSS positioning services: Some problems and proposed solutions

Abstract

Positioning services based on GNSS Permanent Networks (PNs) disseminate the reference frame to users; hence the networks must be adjusted by constraining the ITRF coordinates of some permanent stations (PS), with the satellite orbits and clocks constrained to the values published by the International GNSS Service (IGS). Furthermore, the positioning service provider must use analysis methods, conventions and practices fully consistent with IGS standards. In this framework some problems arise. A first one is that long term solutions for the IGS PS coordinates are not always fully consistent with weekly IGS products, requiring an appropriate use of IGS PS weekly solutions. Moreover, the consistence of the reference frame implied by di¤erent positioning services must be checked, to avoid discontinuities between neighbouring networks. Clearly, in order to monitor the PS coordinates, the adjustment of a network needs to be performed on a quasi real time continuous (daily or weekly) basis. However, from a practical point of view, a continuous update of the PS coordinates is neither appropriate nor possible and alternative proposals will be presented. Finally, most users of real-time positioning services need coordinates in another reference frame, perhaps a local one or the national one. In this case the realtime service provider must distribute the transformation between the broadcasted frame and the user required reference frame. In this work some possible solutions of the aforementioned problems are presented, based on experiences obtained during data processing and adjustments of the Piemonte and Lombardia (Northern Italy) networks.

Global and local reference frames

“…ETRF2000 is the local reference frame adopted in Europe (see, for example, Benciolini et al 2008), as last, reliable realization of the European Terrestrial Reference System 89 (ETRS89), according to the recommendation of the EUREF (IAG sub-commission for the European Reference Frame) Technical Working Group (Boucher and Altamimi 2011). ETRS89 is defined in the EUREF Resolution 1 taken in Florence, Italy, on 28-31 May 1990 (EUREF 1990), as the system coincident with ITRS at the epoch 1989.0 and fixed to the stable part of the Eurasian Plate, after having recognized that in ITRF89 station positions in the stable part of Europe had a common motion of the order of 1 cm per year (so that there is a clear spatially correlated secular displacement field due to tectonics).…”

Frame transformation and geoid undulation transfer to GNSS real time positions through the new RTCM 3·1 transformation messages

“…41.00 network adopts dynamic reference frames, it could produce jumps in station positions or discontinuities that are not practical for end users, [2]. So, a NTRIP stream with a 1021 message could be implemented in order to broadcast to users the seven-parameter transformation that aligns updated GNSS reference station coordinates with the previous solution in ETRF89 coordinates (obtained from previously adopted ITRFxx).…”

Are local active networks a reliable densification of national RTK positioning network? A case study in Spain

“…The single baseline solution, also known as the single reference station (SRS) solution, uses one reference station (base station) to obtain correction data accessible either by radio transmission or via the internet. Common error sources associated with the use of a temporal base station, including inaccurate base coordinates, incorrectly plumbed base antenna and erroneous measurement of antenna height, are avoided by the use of a continuously One aspect of particular relevance in an active network is to know the reference frame that is being transferred to users (Benciolini et al, 2008). The basis is a particular realization of the ITRS (International Terrestrial Reference System).…”