Quality Analysis of the NTv2 Coordinate Transformations with Geosoftware by KilletSoft
Practice-oriented Accuracy Verification of the Software TRANSDAT and GeoDLL
with an extremely structured NTv2 Grid File.
(firmenpresse) - The Coordinate Transformation Program TRANSDAT and the Geodetic Development Kit GeoDLL support the NTv2 standard for Coordinate Transformations with high accuracy. For this purpose TRANSDAT uses the Dynamic Link Library GeoDLL as a basis for all geodetic calculations. Already in 2010, Geosoftware by KilletSoft was tested for the accuracy in calculations with the then-current NTv2 grid file BeTA2007. The result of this analysis is documented on the website http://www.killetsoft.de/t_1005_e.htm. Since then, the requirements on Geosoftware regarding the transformation of geodata of the real estate cadastre have increased. For this purpose almost all federal states provide highly accurate, close-meshed NTv2 files. The most recent examples are the cadastral-exact NTv2 solutions of the federal states Bavaria and Baden-Württemberg. Read more about it in my publication on http://www.killetsoft.de/t_1704_e.htm.
For a current quality analysis and in collaboration with the engineering office KilletSoft the biggest German network operator Westnetz GmbH has again conducted comparative calculations with TRANSDAT / GeoDLL. The NTv2 file used for the quality analysis has been compiled by Westnetz for the conversion of all inventory data with spatial reference. The NTv2 file allows Coordinate Transformation with cadastral accuracy on the basis of official solutions in the area of the old German federal states (without Berlin). The NTv2 file contains 64 sub and sub-sub grids with over 7 million data lines in total. For testing purposes a coordinate file with a grid of 4,328,291 points for transformations from Gauß-Krueger/DHDN90 to UTM/ETRS89 has been generated. FME (Feature Manipulation Engine by the Canadian company Save Software) was used as reference software for comparative calculations and quality assurance measures.
Based on comparative calculations of 4.3 million coordinates with TRANSDAT / GeoDLL and the reference software, the quality could be tested in terms of the following criteria:
•Calculation accuracy over the entire surface
•Identity of forward and backward calculations
•Correctness in border areas of the NTv2 grid file
•Transformation performance with big data volume
Calculation accuracy
More than 4.3 million points were transformed with TRANSDAT / GeoDLL and the reference software from Gauß-Krueger/DHDN90 to UTM/ETRS89, and then compared afterwards. There were no deviations bigger than one millimeter. Such minor deviations (0-1mm) are tied to mathematic tolerances and internal rounding of the used software.
Identity of forward and backward calculations
For this test the coordinates were transformed from the source system Gauß-Krueger/DHDN90 into the target system UTM/ETRS89. Afterwards, the result was calculated back to Gauß-Krueger/DHDN90 and compared to the source coordinates. The NTv2 documentation shows that during back transformation it is not possible to find the same grid mesh for every coordinate in border areas of the grids. As expected it leads to a few minor deviations:
Category Number
---------------------
0-1mm 4327562
2-3mm 712
3-5mm 2
5-7mm 1
7-9mm 1
9-10mm 1
1-2cm 3
2-3cm 3
3-5cm 3
5-6cm 1
6-7cm 2
---------------------
Total: 4328291
If deviations less than three millimeters are explained by mathematic tolerances and internal rounding of the used software, then 17 calculations with a deviation between three millimeters and 6.4 centimeters remain. This equates to an extremely low rate of only 3.9 ppm or 0.0039 per mill.
Correctness in border areas
The tested NTv2 file contains 64 sub and sub-sub grids. In the western and southern border areas of the sub grids the calculation is quite complicated. This particularly applies when a coordinate lies exactly on a boundary line. Many of the 4.3 million calculated points have been intentionally placed into the border areas. Compared to the reference software there were no remarkable deviations.
In this context the trouble ticket number 209 of the Open Source Library Proj.4 is pointed out. It says that the NTv2 module in Proj.4 does not transform correctly in a minimal area around the edges of the coordinate grids due to a bug when the NTv2 file contains several sub grids. It states it might apply to a lot of programs which contain Proj.4 for geodetic calculations. But GeoDLL and TRANSDAT by KilletSoft use own algorithms for NTv2 calculations and thus they are not affected by the above mentioned error!
GeoDLL and TRANSDAT are the only software on the market which allows the consideration of polygonal validity scopes in NTv2 grid files. Coordinates located outside of a polygon can be excluded from the calculation. For example, the polygon can be the boundary of an investigated area or administrative area. In the publication “Proposal for using Polygonal Validity Scopes in Ntv2 grid files“ on http://www.killetsoft.de/t_1512_e.htm you can read how a NTv2 file is prepared for this purpose.
Transformation performance
The project management of Westnetz has conducted an extensive documentation as part of the quality analysis. Among others, Westnetz stressed the excellent calculating speed of TRANSDAT / GeoDLL. Despite a volume of 4.3 million test data and the usage of the very large NTv2 file of Westnetz, the software worked with high performance and very precisely. Dynamic Link Library GeoDLL used by TRANSDAT for geodetic calculations is very fast due to optimized C Programming.
Result of the quality analysis
The good result in all areas of the quality analysis is not surprising because only strict formulas are used for geodetic calculations. The Coordinate Transformations are conducted based on publications by Maarten Hooijberg (1997 and 2008). The NTv2 geodetic datum shift is carried out based on the publication by D. R. Junkins and S. A. Farley (1995), “NTv2 - National Transformation Version 2 - User’s Guide“.
Are you interested?
You can find detailed information about the Coordinate Transformation Program TRANSDAT and the Geodetic Development Kit GeoDLL on the website http://www.killetsoft.de and you can download free trial versions there. The website also shows a worldwide compilation of NTv2 files that are freely available and can be downloaded directly there. Worldwide all NTv2 grid files and thousands of Coordinate Systems and Datum Shifts are supported by TRANSDAT and GeoDLL.
Themen in dieser Pressemitteilung:
Unternehmensinformation / Kurzprofil:
Killet Software Ing.-GbR - short: KilletSoft - is a software company, which was established in the year 1991 and offers exclusively geodetic engineer power. The society is divided in the divisions "Geodetic Software", "International Geodata" and "Development Tools for Geoinformatics". The focal trades of the companies supplied by KilletSoft are consulting engineers, GIS developers, Internet marketing, public utilities, logistics, telecommunications, security and public services. We deliver not only to customers in the Federal Republic of Germany, as well we are presented in the European countries, the United States, Canada, Australia and worldwide. Our software is always documented in English and German, usually also in many other languages.
Within the division "Geodetic Software" KilletSoft is focusing on the development of user friendly geodetic applications. By our online presence in the Internet these applications benefit very strongly from the user feedback. We develop applications, in which again and again incorporate the suggestions and desires of the users and thus lead to meaningful updates of the software. Particularly proud we are on the program TRANSDAT, which can accomplish worldwide geodetic coordinate-transformations and datum-shifts between the unbelievably lots of different state-specific systems, and which has reached a high name recognition in the meantime.
KilletSoft distributes "International Geodata" with georeferences, which refer to spatial structure objects with different resolutions. The georeferences are present as coordinates of towns and urban districts, postal code areas, dialing code areas, nature areas, landscapes and climatic zones. In each case they are linked with the suitable hierarchical political units and additional data. The geodata are available for almost all countries of the world. The georeferences are contained as geographical coordinates, UTM coordinates and for the Federal Republic of Germany additionally as Gauss Krueger coordinates. The databases require an intensive data administration to ensure constant topicality. They are at least annually updated.
An important field of activity of KilletSoft is the enhancement and maintenance of the "Development Tools for Geoinformatics" in form of libraries, DLLs and source codes. The development tool GeoDll offers geodetic functions like e.g. different Coordinate Transformations, geodetic datum shifts and distance computations for the integration into own applications, which may be written with any programming language. With the programs NTv2Tools and NTv2Poly we offer the possibility to convert, select and otherwise modify any NTv2 files in various ways as well as to create Polygonal Validity Scopes in NTv2 files. Our development tools are constantly supplemented and improved by user suggestions and desires.
Killet Software Ing.-GbR
Escheln 28a
47906 Kempen (Germany)
Tel: +49 (0)2152 961127
Mobil: +49 (0)1577 5395448
Email: killetkilletsoft.de
Killet Software Ing.-GbR
Escheln 28a
47906 Kempen (Germany)
Tel: +49 (0)2152 961127
Mobil: +49 (0)1577 5395448
Email: killetkilletsoft.de
Datum: 22.09.2018 - 09:23 Uhr
Sprache: Deutsch
News-ID 581399
Anzahl Zeichen: 6882
contact information:
Kategorie:
Software
Typ of Press Release: Produktinformation
type of sending: Veröffentlichung
Date of sending: 22.09.2018
Anmerkungen:
Dear Sir or Madam,
I ask to make the here described feature article available to our readers by publishing it on your media.
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A ZIP file with the article as MS-WORD file and as PDF file and with all images in different resolutions and graphic formats for the purpose of publication in a print or online medium can be downloaded from the address http://www.killetsoft.de/zip/presse/pr1705_e.zip.
The text and the images of the article are expressly fully available without any restriction for publication. All content may be shortened, supplemented and altered as long as it does not distort the meaning of the content. I declare that KilletSoft is in possession of all rights to the text and images of the article.
If you publish, it would be nice to get an author's copy.
Fred Killet
Killet Software Ing.-GbR
Escheln 28a
47906 Kempen (Germany)
Tel: +49 (0)2152 961127
Fax: +49 (0)2152 961128
Mobil: +49 (0)1577 5395448
killet(at)killetsoft.de
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