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Internet searches often imply that the Reference System WGS84, which is used with GPS measurements, and the European Reference System ETRS89 are virtually identical and that coordinate transformation between the two systems is unnecessary.
In fact, the positions calculated by these two Reference Systems currently deviate by more than half a meter.
For the purposes of navigation or geo infonomics, this does not present a problem as here the need for precision is negligible, and thus a conversion between the two systems is superfluous.
However, for high-precision surveying work within the framework of geodesic spatial referencing and for data with legal effects, like the Land Survey Register, this difference must be accounted for.
This article addresses the following two questions:
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Abbr.: CRS Coordinate Reference System A CRS contains two different elements - the Coordinate System and the Reference System (datum). The Coordinate System describes how the coordinates of the CRS are expressed by calculation rules and projection equations. Examples: Ellipsoidal coordinates, Cartesian coordinates, UTM, Gauss Kruger. The Reference System defines how the CRS is related to the earth. Examples: ED50, DHDN, ETRS89. |
The Reference System WGS84, used for GPS measurements, is based on the global International Terrestrial Reference System ITRS that is fixed on the earth's center of mass.
Due to plate tectonics, the Eurasian continent within the ITRS is slowly moving upon the surface of the earth in a north-easterly direction.
ETRS89 is a geocentric Reference System for Europe based on the state of the International Terrestrial Reference System ITRS as of January 1, 1989.
As the Eurasian continental plate is largely static, ETRS89 provides Europe with a Reference System that is uniform and time-independent.
The relationships between coordinates located on the stable part of the European plate thus remain unaltered with ETRS89.
Since ETRS89 was realized, a shift of 50 to 60 centimeters has accrued between WGS84/ITRS and ETRS89 which continues to grow dynamically at a rate of approximately 2.5 centimeters annually.
The difference varies depending upon the location of a given coordinate on the Eurasian plate because, in addition to the shifting, rotation also takes place.
The vectors representing shifting and rotation are graphically depicted in image 1 (Source: Wolfgang Augath; Beiträge des Vermessungswesens...).
GPS satellites furnish signals by which positions worldwide can be accurately determined within about 10 meters.
With the help of satellite positioning services such as SAPOS and its specifications HEPS, GPPS and GHPS, for instance, a joint project of the working groups of the surveying authorities of the German federal states, can increase the positioning accuracy to within mere centimeters.
The satellite positioning service ASCOS, developed by AXIO-NET GmbH, or the Federal Office for Cartography and Geodesy's reference network GREF can also improve the positioning accuracy to within this range.
Frequently results generated by these services are provided already as ETRS89 coordinates.
For the transformation of GPS coordinates from the WGS84/ITRS Reference System to ETRS89, transformation parameters are required that support such high accuracy.
To this end, precise parameter sets are calculated and regularly made public as ITRS annual realizations or WGS84 epochs.
The WGS84/ITRS GPS coordinates are converted to ETRS89 with their given epoch's parameter set.
For an exact calculation, it is therefore necessary to know the epoch, that is, the year the GPS data was implemented.
These realizations are issued using the year in the form of ITRS89 for the year 1989, successively up to ITRS10 for the year 2010.
The latest version of KilletSoft's TRANSDAT coordinate conversion program provides a module that can carry out very precise coordinate transformations from current GPS measurements to the Reference System ETRS89 using the parameter set ITRS10 for the year 2010.
In addition, the program enables the transformation of GPS coordinates of any older or future epochs to ETRS89.
The ITRS parameter sets available in TRANSDAT will also be dynamically continued in the coming years.
To align GPS coordinates, it is also possible to transform data from one WGS84 epoch to another.
Various Geographic notations and UTM coordinates are used as Coordinate Systems.
If necessary, the transformation of ETRS89 coordinates can be made to the local systems off all European countries in a second step, such as German Gauss-Kruger coordinates using the Reference Systems DHDN, RD, PD and S42.
For example, here will be shown how to convert highly accurate GPS coordinates from an earlier epoch to the Europe-wide CRS UTM/ETRS89 specified by INSPIRE with consideration of the continental drift.
It is assumed that a large amount of GPS coordinates are stored line by line in a text file.
The coordinates are present as Geographic Coordinates in the nautical notation (degrees, minutes) in WGS84 datum as customary for GPS coordinates.
The GPS campaign took place in 2001.
The following settings must be made in the program TRANSDAT to convert the GPS coordinates to the CRS UTM/ETRS89:
Then a click on the button 
opens the window for the file settings.
There all necessary settings for the input file and for the output file can be made.
Clicking the button 
starts the coordinate transformation.
After a few seconds accurately calculated results with consideration of the continental drift between the years 1989 and 2001 are contained in the output file named before.
To incorporate the geodesic calculations used by the TRANSDAT program into programs of your own, the GeoDLL dynamic link library is at your disposal.
All of the geodesic calculations included here are based on strict formulas that we use to attain high-precision results.
GeoDLL also includes the ITRS parameter set releases and the essential high-precision transformation routines.
To ensure that the geodesic functions can be implemented on other platforms, the GeoDLL C++ source code is also available.
Thanks to the multilingual user interface and documentation of the software described here, its range of operation is worldwide.
Hundreds of international and national coordinate and Reference Systems from all continents are supported.
The emphasis, however, is on the diverse Coordinate Systems landscape of the Federal Republic of Germany and the Europe-wide coordinate and Reference Systems as predetermined by INSPIRE.
The software is used by engineering offices and GIS developers in all industrial sectors and in public administration to carry out precise coordinate transformation.
You can find additional information and downloadable test versions of TRANSDAT and GeoDLL software at http://www.killetsoft.de.
In order that you always are well informed about our company, we write actual news, current information and special offers here into this column.
Free update on purchasing Geodata Germany
Geodata Germany are updated in March / April every year.
You have no disadvantage if you purchase the data in 2012 before the annual update, because you will get a free update.
NTv2 calculations
KilletSoft provides for their produkts GEoDLL and TRANSDAT encrypted NTv2 files of the Federal States Hesse, Saxony and Thuringia for highly accurate calculations.
Read more ...
Administrative Reform in Mecklenburg-Western Pomerania
The administrative data bases of the Federal Republic of Germany "Geodata Germany" have been updated to the reference date of September 15th, 2011!
The reason therfor are the essential modifications due to the Administrative Reform in the Federal State Mecklenburg-Western Pomerania.
Read the Press Release ...
Win32 and X64
The Dynamic Linc Libraies GeoDLL and BetaDLL supports 32bit and 64bit architecture now.
The DLLs are written in C++ and were developed with Microsoft Visual Studio 2010.
Are the reference systems WGS84 and ETRS89 really identical?
Inclusion of the continental drift for the transforming of GPS coordinates with the software products TRANSDAT and GeoDLL.
Read the Press Release ...
Translators wanted!
The latest versions of the programs TRANSDAT and SEVENPAR support language files for the programs interface.
Since the language dependent texts are managed in external files, new languages can be added at any time by creating new language files.
Every user of the program now can compile language files by himself.
WINDOWS© 7 compatible
Our software has received the certificate "WINDOWS© 7 compatible".
So it complies with the compatibility standards of the Microsoft operating systems WINDOWS© 7.
INSPIRE©
GeoDLL and TRANSDAT supports Europe-wide the ETRS89 coordinate systems proposed by INSPIRE©.
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