Calculation accuracy with NTv2

 

 

Quality check with test data of the ADV

The function library GeoDLL supports NTv2 standard Coordinate Transformations with high accuracy. Amongst others the NTv2 grid file BeTA2007 can be used for transformations within Germany with results in sub-meter accuracy. The grid file is provided by the "Arbeitsgemeinschaft der Vermessungsverwaltungen der Länder der Bundesrepublik Deutschland" (ADV), along with a documentation and a set of test data. The test data contain 31 spaced points on the territory of the Federal Republic of Germany in different variations with coordinates in both Reference Systems DHDN90 and ETRS89.

 

The test data are provided by the ADV for the verification of the computational accuracy of transformation solutions with external software. The results do not make a statement about the accuracy of the transformation system BeTA2007. Due to the system with BeTA2007 a nationwide transformation accuracy in sub-meter range can be realized. For allocated areas even an accuracy in the decimeter and centimeter range can be achieved.

 

Comparative calculations with the test data of the ADV attest GeoDLL a very good self-consistency. Here are the results:

•Forward calculation Gauss-Krueger / DHDN90 to UTM / ETRS89:
Maximum deviation 0,04 millimeters
Average deviation 0,02 millimeters
•Forward calculation Geographic Coordinates DHDN90 to ETRS89:
Maximum deviation 0,51 microseconds (millionth seconds, corresponds appr. 0,01 millimeters)
Average deviation 0,19 microseconds
•Reverse calculation UTM / ETRS89 to Gauss-Krueger / DHDN90 on different meridian strips:
Maximum deviation 0,20 millimeters
Average deviation 0,07 millimeters
•Reverse calculation Geographic Coordinates ETRS89 to DHDN90:
Maximum deviation 0,51 microseconds
Average deviation 0,18 microseconds

 

The good result is not surprising, since for the calculations strict formulas are used only. The Coordinate Transformations are performed according to publications of Maarten Hooijberg (1997 and 2008). The NTv2 date change is made following publications of D. R. Junkins and S. A. Farley (1995).

 

You can download the test protocol and the tables with the corresponding calculations from our server.

 

 

Quality check with an extreme NTv2 file of the network operator Westnetz GmbH

For a current quality analysis and in collaboration with the engineering office KilletSoft the biggest German network operator Westnetz GmbH has again conducted comparative calculations with TRANSDAT / GeoDLL. The NTv2 file used for the quality analysis has been compiled by Westnetz for the conversion of all inventory data with spatial reference. The NTv2 file allows Coordinate Transformation with cadastral accuracy on the basis of official solutions in the area of the old German federal states (without Berlin). The NTv2 file contains 64 sub and sub-sub grids with over 7 million data lines in total. For testing purposes a coordinate file with a grid of 4,328,291 points for transformations from Gauß-Krueger/DHDN90 to UTM/ETRS89 has been generated. FME (Feature Manipulation Engine by the Canadian company Save Software) was used as reference software for comparative calculations and quality assurance measures.

 

More than 4.3 million points were transformed with TRANSDAT / GeoDLL and the reference software from Gauß-Krueger/DHDN90 to UTM/ETRS89, and then compared afterwards. There were no deviations bigger than one millimeter. Such minor deviations (0-1mm) are tied to mathematic tolerances and internal rounding of the used software.

 

The test result and statements on the speed of the calculations can be found in our publication on the Internet at https://www.killetsoft.de/t_1705_e.htm.