Group NTv2 Tools
The group "NTv2 Tools" contains functions that allows the manipulation and data retrieval from NTv2 ASCII grid files and NTv2 binary files.
NTv2 files are either in ASCII format or in binary format. With the functions convntvascii2bin() and convntvbin2ascii() can be converted between the two file formats.
There are some very large NTv2 binary files that are larger than the 2.15 gigabytes addressable with the "long int" C variable type. For example, the Bavarian NTv2 binary file BY_KanU_Bayern-gesamt.gsb has a size of about 3.5 gigabytes. Unlike the Software GeoDLL and TRANSDAT by KilletSoft, many geodetic programs and GIS can not handle such large NTv2 files. With the function convntvbin2area() it is possible to copy an area defined by a coordinate section from a NTv2 binary file into a new binary file. All subgrids of the binary file, which intersects the coordinate section, are taken into account. The new binary file created in this way is smaller and can be used with any geodetic software and GIS.
An NTv2 file contains one or more quasi-rectangular coordinate grids which are defined in the NTv2 headers. Instead of a rectangular area only an embedded polygonal area should and must be covered, for example, a state territory within the country borders. The function convntvbin2polyvalid() realizes the Polygonal Validity Scope in NTv2 files. For that purpose the polygonal scope is realized with a shape file that contains the outlines of the scope as polygons. Coordinates outside the scope then can be excluded from calculations or be acknowledged by a warning using the KilletSoft products TRANSDAT and GeoDLL and a lot of GIS software developed by companies which supports Polygonal Validity Scopes.
Further functions of this group determine the header data of the of NTv2 grid files or their subgrids.
Characteristics of the function group
"NTv2 Tools" function group
Function convntvascii2bin() - Convert a NTv2 ASCII file to a binary file
Function convntvbin2ascii() - Convert a NTv2 binary file to an ASCII file
Function convntvbin2area() - Copies an area of a NTv2 grid file to a new binary file
Function convntvbin2polyvalid() - Supplement of NTv2 binary files with Polygonal Validity Scopes
Function getntvgridarray() - Determination of parameters of one or all NTv2 subgrids in arrays
Function getntvgridcount() - Determination of the count of subgrids contained in a NTv2 file
Function getntvgridheader() - Determination of the header parameter of one or all NTv2 subgrids
Function getntvheader() - Determination of the header parameter of a NTv2 file