GeoDLL - Function Groups
At present 2 to 7 cm per year
GeoDLL supports the development of geodetic software by providing geodetic functions, which are put together into function groups for specific tasks. To use highly accurate coordinate transformations with NTv2 grid files in own developments a license for the additional function group "NTv2 Transformations" can be purchased. Requirement for the use of this function group is a license of the function group "Coordinate Transformations".
NTv2 means "National Transformation Version 2". The NTv2 method uses binary files to perform accurate datum shifts from one geodetic Reference System to an other. An NTv2 file contains the differences between the two Reference Systems as geographic seconds in a grid. A bilinear interpolation is used to calculate the exact coordinates for a point in the target Reference System.
Depending on the geographic coordinate NTv2 can check several grids contained in the file for the information with the highest accuracy. An NTv2 file always contains a single-precision base grid (parent). Certain areas, such as cities, can be included in the file as local grids with a higher grid density and thus higher accuracy. These local grids overlap areas of the base grid. If a point lies within one of the grids with the higher accuracy, NTv2 will use it, otherwise the point will fall through to the base grid with the lower accuracy.
A description of the NTv2 algorithm can be found in the following sources:
The NTv2 grid files supported by the program TRANSDATpro and the function librariy GeoDLL you can download here from the KilletSoft website!
The program TRANSDATpro and the function librariy GeoDLL supports NTv2 standard Coordinate Transformations with high accuracy. Amongst others the NTv2 gridfile BeTA2007 can be used for transformations within Germany with results in sub-meter accuracy. The gridfile 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.
Comparative calculations with the test data of the ADV, done by the engineering office Killet Software Ing.-GbR, attest to the software TRANSDATpro and GeoDLL a very good self-consistency. Here are the results:
You can download the test protocol and the tables with the corresponding calculations from our server.
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 TRANSDATpro / 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 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 TRANSDATpro / 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.
Detailed descriptions of all geodetic functions of this function group you find here in the online manual!