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GeoPosition - Further Information

Coordinate- and Datum-Transformation

For all coordinate systems based on transverse Mercator (UTM, Gauss-Krüger, MGRS, GGRS87, LUREF) the formulas of Prof. Dr. Louis Krüger, published in „Konforme Abbildung des Erdellipsoids in der Ebene, Neue Folge 52, Potsdam 1912“, are used. For UPS the formulas for stereographic projection, published by John P. Snyder in „Map Projections - A Working Manual, USGS Professional Paper 1395 (1987)“, are used. For Mercator projection the formulas, published in Wikipedia, are used.

For the datum shift, the Helmert-Transformation is used, as published in „OGP Publication 373-7-2 – Surveying and Positioning Guidance Note number 7, part 2 – November 2010, Coordinate Conversions and Transformation including Formulas“.

For the coordinate systems Swiss Grid CH1903+/LV95 and CH1903/LV03-M (Schweizer Landeskoordinaten) the formulas are used, which are published by the Swiss Federal Office of Topography in the document "Formulas and constants for the calculation of the Swiss conformal cylindrical projection and for the transformation between coordinate systems, October 2008“.

Reference Applications

The following reference applications can be used to verify the calculations of GeoPosition before you report an error in calculation:

  1. NGA Web GEOTRANS - Web application of the National Geospatial-Intelligence Agency for coordinate transformation of  many projection systems and datums. GeoPosition doesn‘t use the programming library of MSP GEOTRANS and partly other formulas. So this application is very useful to verify the calculations. MSP GEOTRANS uses the Molodensky transformation for datum shift. Therefore there may be a slight deviation in the results (< 1m). MSP GEOTRANS implements a 7-parameter and a 3-parameter variant for the datums „EUROPEAN 1950, Mean“ and „ORDNANCE GB 1936, Mean“. GeoPosition implements only the 7-parameter variants. Further, MSP GEOTRANS uses different parameters for the datum „ORDNANCE GB 1936, Mean“ as GeoPosition (see below). Therefore you get greater deviations with these datums.

  2. GeoConvert - Supports the projection systems UTM, UPS and MGRS but no datum shift.

  3. Spreadsheet Converter - EXCEL spreadsheet and JavaScript application to convert UTM coordinates.

  4. Geographic/UTM Coordinate Converter - Web application (JavaScript) to convert UTM coordinates.

  5. Coordinate transformation of the German Federal Agency for Cartography and Geodesy -  Java-Applet application to convert Gauss/Krüger coordinates with the datum DHDN (Deutsches Hauptdreiecksnetz) Potsdam/Rauenberg

  6. REFRAME swisstopo - Web application of the Swiss Federal Office of Topography to convert coordinates of the Swiss Grid systems CH1903+/LV95 and CH1903/LV03-M

Datum Lists (Geodetic Systems)

GeoPosition implements over 280 datums published before 03/2011 on the following lists:

  1. - Parameters for over 200 map reference systems

  2. NGA Map Datum Overview - Datum lists of the National Geospatial-Intelligence Agency

  3. NATO/STANAG 2211 -  NATO datum list, from which especially the 7-parameter variants are used

  4. Ordnance Survey - Source for the 7-parameter datum „ORDNANCE GB 1936, Mean“

  5. German Federal Agency for Cartography and Geodesy - Source for the 7-parameter datum DHDN (Deutsches Hauptdreiecksnetz) Potsdam/Rauenberg

For the datum „EUROPEAN 1950, Mean“ the 7-parameter variant of the MSP GEOTRANS library is used and for the datum „ORDNANCE GB 1936, Mean“ the 7-Parameter variant published on the web site Ordnance Survey. Generally the 7-parameter variant of a datum is preferred (e.g. from the NATO datum list) when both variants are published. So, this results in deviations to calculations with the 3-parameter variants of these datums, especially when they are used outside their dedicated regions.

If you need further datums in GeoPosition, list at least one reliable source for the datum. These datums will be implemented promptly in the next version.