Coordinate reference systems (CRS) are essential for combining spatial data in maps and in GIS. So it is an important task of survey administrations to provide users with easy to use reference systems for their daily work. CRS usually are theoretically defined as reference systems and realized physically by monuments. This realization are called reference frames. Examples are the International Terrestrial Reference System (ITRS) and the International Terrestrial Reference Frame (ITRF).

All the classic reference systems have been realized by using the latest technology for measurements, which has been triangulation until approx. 1970 and then trilateration until GPS comes up for long distance measurements in the late 1980th. All the classical measurements (angles and distances) are very precise in a close neighbourhood, but not absolutely. With global navigation satellite systems (GNSS) we now have the possibility for precise positions independent from distances and it is easy for everyone to determine precise positions everywhere. Now the task is to adjust absolutely accurate data to reference systems that are precise only locally. Therefore mostly 7 parameter transformations (7PT) are in use. The result of each 7PT is depending on the control points used and not suited to adjust large areas precisely.

For users who have to combine own data with administrative data or for users that have to combine data based on a given reference system, it is essential to have a common transformation which is unique for big areas, e.g. for a country. Such transformations can be applied by using a grid based approach. An example therefore is the NTv2 transformation developed for Canada which can be applied for any area. It is able to model and adjust local distortions in CRS in a unique way.

In Germany the NTv2 approach is used for transforming topographic data based on the current geodetic datum Deutsches Hauptdreiecksnetz (DHDN) into the new European Terrestrial Reference Frame (ETRF 89).

Within the next years all locally precise cadastral data has to be transformed and improved from DHDN to absolutly precise ETRF 89. In the authors opinion NTv2 will be the best solution for this task. Therefore the German states have to publish local NTv2 grid files which are harmonized at the states boudaries.

 

References

 

CRSeu: Coordinate Reference Systems in Europe, Available: http://www.crs-geo.eu, Accessed, March, 14, 2011)

 

Working Committee of the Surveying Authorities of the States of the Federal Republic of Germany: ETRS89/UTM – Transformation, http://www.adv-online.de/icc/extdeu/broker.jsp?uMen=2b8702f6-5f2f-dc21-8f7f-8f272e13d633, Accessed; March 14, 2011)

 

Werner Flacke: NTv2 für Deutschland, http://support.esri.de/files/support/NTv2inArcGIS_Deutschland.pdf [Accessed: July 24, 2011]

 

Arbeitsgemeinschaft der Vermessungsverwaltungen der Länder der Bundesrepublik Deutschland (AdV): Bundeseinheitliche Transformation für ATKIS (BeTA2007), Version 1.4, Stand 16. Februar 2010, http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/BETA2007dokumentationV14.pdf [Accessed: July 24, 2011]