GPS Network Services For Supporting Surveying Tasks.
Joël van Cranenbroeck
Director GPS Reference Station Program,
Leica Geosystems AG,
Heinrich-Wild-Strasse CH-9435 Heerbrugg, Switzerland
Tel: (32) 8141 2602, Fax: (32) 8141 2602
Email: Joel.VanCranenbroeck@leica-geosystems.com
Introduction
It is well recognized today that a reference network comprised of permanent GPS stations provides the fundamental infrastructure required to meet the needs of professional GPS users in many areas of surveying and mapping. Examples of applications are found in survey control work, densification of existing geodetic networks, acquisition of data for GIS applications, cadastral operations, determination of fiducial points for photogrammetric work, monitoring of engineering works, mapping of utility corridors, assets, etc. In fact, the number of applications benefiting from the establishment of permanent networks is growing daily and in addition there is a new driving force, the non-survey community, who are demanding service.
The widespread use of RTK GPS and DGPS techniques has encouraged decision-makers to look for ways to replace traditional geodetic networks with networks of permanent GPS reference stations and save money. For example, a tighter control of the networks can be achieved from the data supplied by permanent reference stations both in post-processing and in real-time. With streaming data, the influence of those spatial and temporal errors affecting GPS measurements can be estimated in real-time. This in turn means the quality of the transmitted corrections is improved and the range of RTK GPS increased.
New methods have also been introduced to increase the performance and throughput of permanent networks investigated by the academic research centres as the University of Hannover in Germany, the University of Calgary in Canada and the University of New South Wales University in Australia. Private firms have become synonymous in the surveying community for their respective approaches in implementing local area corrections and so-called virtual reference station techniques.
Additionally, discussions taking place within the RTCM organization aim to introduce new standards for the broadcast of GPS corrections specifically for Network RTK messages. Leica has been actively involved with the working group responsible for this message standardization.