Proposal for using Polygonal Validity Scopes in NTv2 grid files

Persbericht: TRANSDAT


Proposal for using Polygonal Validity Scopes in NTv2 grid files



Preface
By means of NTv2 grid files it is possible to transform points from one coordinate reference system to another with very high accuracy. A 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. How can outside of a polygonal administrative area located coordinates be excluded from the coordinate transformations and reference system transitions (datum shifts) and thereby localization errors be suppressed? The author presents a simple but effective solution for this problem. The article matches GIS developers who generate NTv2 files for accurate reference system transitions in administrative areas. It also addresses GIS users who perform coordinate transformations and reference system transitions using NTv2 files.

Summary
The author presents a simple method for realizing polygonal validity scopes in NTv2 files. Thereby the structure of the NTv2 file remains unchanged. When generating NTv2 files, grid meshes that are located outside of the polygonal validity can be labeled with exopolygonal entries. The benefit of this method is the exclusive addressing of grid meshes inside the intended administrative area and thus the exclusion of localization errors. Software developers can implement the consideration of polygonal validity scopes in GIS software by a few changes in the source code. KilletSoft already provides GIS software which supports polygonal validity scopes.

The whole article is available at http://www.killetsoft.de/t_1512_e.htm.

Killet Software Ing.-GbR
Postbox 40 02 25
47896 Kempen
Germany

Source: http://www.killetsoft.de/t_1512_e.htm