Geocomp Systems
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GeoCalc 4.20


GeoCalc 4.2 converts ASCII coordinate data files between commonly-used mapping systems.

GeoCalc 4.20 is a companion for Geocomp, GeoNav, or any other point-based spatial data system that doesn't already have a coordinate converter.

GeoCalc 4.20 is a free download.

Note that there are other programs with similar names that do similar things.

If you require NTv2 grid database transformations, consider our Trimble Terramodel with GCCOORD.


  • Converts coordinate data files between commonly-used mapping systems.
  • Uses seven-parameter transformations.
  • Has user-definable parameters allowing deployment anywhere in the world on almost any spheroid or mapping system.
  • Includes a large number of predefined mapping systems and spheroids.
  • Includes Geocentric Datum of Australia.
  • Compares geodesy of the same point in two different mapping systems.
  • Displays geographic, geocentric and projection coordinates of three dimensional points in any defined Mapping System.
  • Displays point scale factor and grid convergence.
  • Is a 32-bit Windows application.
  • Includes complete documentation in Help (assuming that you understand the concepts).
  • Is Copyright © Geocomp Systems.
  • Is downloadable free of charge from the web.
  • Is included on our Terramodel 10.61J DVD.
  • Was released in November 1999.

Examples of supported mapping systems

  • Local Grid - chose your own
  • Mercator
  • Transverse Mercator - Australia (AMG, ISG, MGA), NZ, Germany, Canada, USA, Great Britain and Russia
  • Stereographic - Polar regions, Nederlands, Hungary, Poland
  • Lambert 1 Parallel - France, Belgium, Denmark
  • Lambert 2 Parallel - World Aeronautical Charts
  • Cassini-Soldner
  • Gnomic
  • New Zealand Map Grid
  • Skew Orthomorphic

Some of the predefined spheroids

  • WGS84
  • WGS72
  • WGS99
  • Australian GDA94/MGA94
  • Bessel 1841
  • Malaysia Kertau 1948 Everest Modified
  • North American Datum 1983

File Formats

Geocalc supports a wide range of ASCII text coordinate formats for import and export. Coordinates can be expressed as Latitudes and Longitudes, Easting and Northing or X,Y,Z.

The following coordinate file formats are predefined:

  • Geocomp Spatial Data System (.PTS & .STR)
  • Geocomp Field File (.FLD)
  • GeoNav Coast File (.CST)
  • UKOOA P1/90
  • X Y Z


  • Download gcalc420.exe (2 MB).
  • Uninstall any previous versions of GeoCalc using Control Panel.
  • Run the self-extracting gcalc420.exe.
  • Unzip the files to the default location, or enter a temporary location like C:\Temp.
  • Run setup.exe from your location.
  • For Windows versions after XP, download and install WinHlp32.exe.
  • Select GeoCalc from the Windows Start Menu or Apps.
  • Select Index from GeoCalc Help for instructions.
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