GeoDLL - Geodetic Development Kit
Additional function group "NTv2 Transformations"

•  Detailed Description of the current Version
•  Descriptions of the GeoDLL Function Groups
•  User Manual with all Function Descriptions
•  User Manual searching for expressions
•  List of Coordinate and Reference Systems
•  Download of the supported NTv2 / HARN grid files
•  Programming example  Group Prices GeoDLL
•  Download  Place order

GeoDLL - Support of the NTv2 standard

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:

1. Junkins, D.R., and S.A. Farley, NTv2 Developers Guide; Geodetic Survey Division, Natural Resources Canada, 1995.
2. Junkins, D.R., and S.A. Farley, NTv2 Users Guide; Geodetic Survey Division, Natural Resources Canada, 1995.
3. Staatsbetrieb Geobasisinformation und Vermessung Sachsen,  Geobasisinformation und Vermessung.

Download of the NTv2 grid files in binary format

The NTv2 grid files supported by the program TRANSDATpro and the function librariy GeoDLL you can download  here from the KilletSoft website!

Accuracy check with the BeTA2007 test data of the ADV

The program TRANSDATpro and the function librariy 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.

Comparative calculations with the test data of the ADV, done by the engineering office Killet GeoSoftware Ing.-GbR, attest to the software TRANSDATpro and GeoDLL a very good self-consistency. Here are the results:

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

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

Accuracy 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 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.

Characteristics of the additional group "NTv2 Transformations"

1. Predefined NTv2 Reference Systems
2. Embedding of any NTv2 grid files
3. Support of Polygonal Validity Scopes in NTv2 files
4. Use of ASCII grid files (.gsa) and binary grid files (.gsb)
5. Automatically allocation of NTv2 files from a common directory
6. Download of many NTv2 files from the KilletSoft website
7. Links to NTv2 providers on the KilletSoft website
8. HARN grid files of the U.S. supported as equivalent NTv2 grid files
9. Free use of some NTv2 files, which otherwise are available for a fee
10. Access to NTv2 files, which are specially licensed for KilletSoft

Functions of the additional group "NTv2 Transformations"

1. Function getntvbinaryfile() - Determination of NTv2 file names matching reference system
2. Function getntvdirmatch() - Determination of a matching NTv2 file in a common directory
3. Function getntvrefbelong() - Determination of the second NTv2 Reference System
4. Function getntvrefequiv() - Determination of an NTv2 equivalent Reference System
5. Funktion getntvrefstatus() - Determination of the NTv2 membership of a Reference System
6. Function setntvbinaryfile() - Test and initialize an NTv2 binary file
7. Function setntvbinautodir() - Set directory for the automatically use of NTv2 binary files
8. Function setntvbinautofile() - Provide an NTv2 binary file in a wait position
9. Function setntvpolyvalid() - Set Polygonal Validity Check in NTv2 files
10. Function closentvbinaryfile() Close NTv2 binary file and free NTv2 instance

Ausführliche Funktionsbeschreibungen

Detailed descriptions of all geodetic functions of this function group you find here in the online manual!