NTv2Poly - Inserting Polygonal Validity Scopes into NTv2 Binary Files using Outlines from Shape Files

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NTv2Poly geosoftware replaces the rectangular activity scope contained in NTv2 files with a Polygonal Validity Scope, which is realized with an outline file in classic Shape Format. Invalid calculations outside the Polygonal Validity Scope thus can be excluded or acknowledged by a warning.

NTv2Poly - Version 7.03 - Last update on 15 June 2024
The latest larger changes History of Modifications and Supplements

Four new menu items with links to topic-related worksheets.
Certification of the program and the installer renewed.
New work sheet about the utilization of the program NTv2Poly..
Added NTv2 files and shape files from Canada and Germany for testing.
Added a new graphics windows "Area Distribution" and "Polygonal Validity Scope".

Polygonal Validity Scopes

Main Window of the program NTv2Poly

Main Window

Distribution of Areas as Example of Canada

Distribution of Areas

Polygonal Validity Scope as Example of Canada

Polygonal Validity Scope

Using NTv2 grid files it is possible to transform points from one coordinate reference system to another with very high accuracy. An NTv2 file contains one or more quadrangular 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 program NTv2Poly realizes Polygonal Validity Scopes in NTv2 files. Using so prepared NTv2 files, coordinates outside the validity scope can be excluded from calculations or they can be acknowledged by a warning. This works with coordinate transformations using the geospatial software TRANSDATpro and GeoDLL by KilletSoft and with many GIS programs which support Polygonal Validity Scopes.

NTv2Poly - Detailed Program Description
Inserting Polygonal Validity Scopes into any NTv2 Binary Files using outlines from classic Shape Files

The Polygonal Validity Scope is realized with a shape file, which contains the outlines of the scope as polygons. The file format Shape is developed by ESRI as a format for geographical objects. For example, in the shape file the border outlines of a country may be stored, which represent the polygonal scope for the NTv2 file used in that country. Using the program NTv2Poly the polygons of the shape file and the quadrangular surface of the NTv2 file are superimposed one on the other and processed in an ingenious manner.

The term "exopolygonal entry" used in the course of the text stands for the entry of a characteristic value in a grid mesh of an NTv2 file to exclude this grid mesh from the scope of the NTv2 file. It follows that all grid meshes with exopolygonal entries are invalid. The program NTv2Poly marks all grid meshes that lies outside the polygons of the used shape file as invalid by introducing exopolygonal entries in the NTv2 file.

By using exopolygonal entries in the shift values or in the accuracy values of the NTv2 file, there are two methods for realizing Polygonal Validity Scopes, which both are supported by the program. The two methods differ considerably in their effects.

Exopolygonal entries replace the accuracy values of the grid meshes.
Exactly one grid mesh is addressed at the grid point of a coordinate. Exactly this grid mesh is defined by the grid point and addressed regarding the interpolation of a coordinate that lies within. This grid mesh is excluded from the polygonal validity scope of the NTv2 grid.
Exopolygonal entries replace the shift values of the grid meshes.
With a bilinear interpolation the four adjacent grid points of a coordinate are used. Each may contain exopolygonal entries. So, all in all four grid meshes are addressed and each has one grid spacing in northern and southern direction and one grid spacing in western and eastern direction from the grid point. These are the four grid meshes that are arranged around the grid point. Exactly these four grid meshes are excluded from the polygonal validity scope of the NTv2 grid.

The use of Polygonal Validity Scopes is described in detail in our Work sheet "Proposal for using Polygonal Validity Scopes in NTv2 grid files".

The program has a user-selectable multi language interface and comes with extensive online help. The program can be run on most common networks and it is possible to use Terminal Services on WINDOWS Servers. In case of a network installation the clients are installed automatically by the program.

Multilanguage support

The program NTv2Poly is equipped with a modern graphical user interface of which handling is to understand intuitively. For each window detailed help texts can be shown. The detailed electronic documentation of the program NTv2Poly is available in both English and German language. However, the user interface can be represented in many languages. For this purpose, external language files are used. When starting the program, it notes which language files are available in the calling directory. The found languages then are provided for selection in a list box. By creating new language files, new languages can be added by users to the program NTv2Poly at any time.

Network ability

The program NTv2Poly can be run on most common networks. The client installations works automatically. It is possible to use Terminal Services on WINDOWS Servers like e.g. "Citrix Terminal Server".

Pricing, ordering and licensing

Pricing and ordering information can be found in the Price list. For available licensing options have a look to the License page. Order the program with the electronic Order Form.

Download of the test version

The free test version of the program with a detailed user manual can be downloaded as ZIP packed file by the Internet.

Use of an illegal program version

Managing Director Fred Killet explains why you should never use an illegal version of our geodetic program NTv2Poly.