GeoDLL - Function Groups
At present 2 to 7 cm per year
In the context of a training measure we have created a worldwide collection of most official NTv2 links.
Click here for the collection of NTv2 files with the possibility for direct download.
NTv2 (National Transformation version 2) datum shifts are done with grid files which comes in a binary format (GSB) and an ASCII format (GSA). It can transform coordinates between two different geodetic reference systems. The transformation provides heigh actuality and does not require ellipsoidal heights.
The Geodetic Development Kit GeoDLL is prepared for coordinate transformations with arbitrary NTv2 grid files and the North American HARN grid files. However, the HARN grid files of the US states are provided as equivalent NTv2 grid files. All by GeoDLL supported NTv2 and HARN gridfiles can be downloaded from this website.
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.
The accuracy of NTv2 datum shifts with the program TRANSDATpro and the Geodetic Development Kit GeoDLL from KilletSoft has been investigated twice in detail: