NTv2 stands for National Transformation version 2, and describes a binary grid format, used to perform high accuracy datum conversions between coordinates.
The National Transformation format has been developed by Canada's Geodetic Survey Division (GCS). The format has been adapted to several other countries, including Australia.
A single NTv2 file can contain various grids with different accuracies. Software has to be designed in a way that a coordinate is converted using the most accurate grid available. To get the actual datum shift for a coordinate, the 4 closest known coordinates are retrieved from a grid file, and then interpolated using bi-linear interpolation. The default extension for NTv2 grid files is .GSB (Grid Shift Binary). There is also an ASCII variant of this file, which is using the extension .GSA (Grid Shift ASCII).
Eye4Software Hydromagic fully supports NTv2 datum transformations. A collection of NTv2 transformation files is shipped with the product.
In case a NTv2 file for your country is missing, you can download it here. After downloading, extract the .gsb file(s) from the archive, and copy them in the NTv2 folder:
To open the "NTv2" folder, select the "Open Program Data Folder..." option from the "Help" menu in Hydromagic and a Windows Explorer window will open.
Locate the "NTv2" folder and double click. Now you can drag .gsb files here.
For more information on how to add a new map datum with NTv2 transformation, refer to the "Manage Datums" manual page.
NTv2 is used in Australia to convert coordinates between the AGD66 (Australian Geodetic Datum 1966) and GDA94 (Geocentric Datum of Australia 1994) datums, and to convert between AGD84 (Australian Geodetic Datum 1984) and GDA94 (Geocentric Datum of Australia 1994).
A66 National (13.09.01).gsb
National 84 (02.07.01).gsb
NTv2 is used in Brazil to convert coordinates between the Corrego Alegre 1961, Corrego Alegre 1970-72, SIRGAS 2000 and WGS84 datums.
NTv2 is used in Canada to convert coordinates between the NAD27 (North American Datum 1927) and NAD83 (North American Datum 1983) datums.
NTv2 is used in France to convert coordinates between the NTF (Nouvelle triangulation de la France) and RGF93 (RÃ©seau gÃ©odÃ©sique franÃ§ais 1993) datums.
NTv2 is used in Germany to convert coordinates between the DHDN (Deutsches Hauptdreiecksnetz) and ETRS89 (European Terrestrial Reference System 1989) datums.
NTv2 is used in Hungary to convert coordinates between the HD72 (Hungarian Datum of 1972) and ETRS89 (European Terrestrial Reference System 1989) datums.
NTv2 is used in New Zealand to convert coordinates between the NZGD1949 (New Zealand Geodetic Datum 1949) and NZGD2000 (New Zealand Geodetic Datum 2000) datums.
NTv2 is used in Portugal to convert coordinates between the Datum Lisboa, Datum 73 and ETRS89 datums.
NTv2 is used in Spain to convert coordinates between the ED50 and ETRS89 datums on the peninsula and the Balearic islands.
NTv2 is used in Switzerland (Swiss Confederation) to convert coordinates between the CH1903 and CH1903+ datums.
The dataset used to perform the conversions is called CHENyx06.
NTv2 is used in the United Kingdom to convert coordinates between the OSGB1936(Ordnance Survey Great Brittain 1936) and ETRS89 (European Terrestrial Reference System 1989) datums. This conversion grid is also called OSTN02.
NTv2 is used in Venezuela to convert coordinates between the CANOA and WGS84 datums.