Creation of a special NTv2 file for a cable net operator
Kempen (Germany) - May 7, 2025
KilletSoft - Fred Killet
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A network operator runs an electric cable net in Lower Saxony around the German cities of Bremen and Bremerhaven. Gauss-Krüger coordinates in the DHDN reference system (CRS GK/DHDN) are used to determine the position of the cables. For the transformation to UTM coordinates in the ETRS89 reference system (CRS UTM/ETRS89), he uses various Helmert parameter sets of the federal states of Lower Saxony and Bremen. The conversion accuracies vary in the decimeter to meter range.
The aim of the network operator is to use a single transformation basis with high accuracy in centimeter range for his entire network area. As a solution, KilletSoft has proposed the generation of an NTv2 file with several high-precision grids. The federal state of Bremen provides the NTv2 file HBTa2020 with two high-precision NTv2 grids for the cities of Bremen and Bremerhaven. Unfortunately, the state of Lower Saxony does not provide any NTv2 grids. However, it is possible to generate high-precision pass points in UTM/ETRS89 from points in the GK/DHDN using the GNTRANS_NI program of the LGLN (State Office for Geoinformation and Land Surveying of Lower Saxony).
In cooperation with an engineering office three pass point lists of the required areas were generated in the CRS GK/DHDN and the CRS UTM/ETRS89 as 50-meter raster. The point lists with a total of around 1.7 million points were then transformed into geographical coordinates of the DHDN and ETRS89 using the TRANSDATpro program. Suitable NTv2 files were generated from these point lists using the NTv2Creator program. The quality analysis revealed accuracies in the millimeter to centimeter range for the three NTv2 files.
The grids contained in the NTv2 files then had to be merged into a single common NTv2 file. This work was performed using the program NTv2Tools. First, an area comprising the operator's cable network was extracted as a base grid from the NTv2 file BETA2007 of the AdV (Working Group of the Surveying Authorities of the Federal States of the Federal Republic of Germany). The two NTv2 grids for the cities of Bremen and Bremerhaven had to be exported from the NBTa2020 file. The total of six NTv2 grids were then imported in the correct order into a common NTv2 file and provided with hierarchically structured grid names and parent names.
The network operator's requirements were solved with the three programs TRANSDATpro, NTv2Creator and NTv2Tools. Detailed information on these programs can be found on the website https://www.killetsoft.de. KilletSoft's time expenditure for this work and the subsequent tests amounted to approx. 14 hours.