Proj4: A nice tool for coordinate transformations

Proj4 is an excellent little utility for coordinate conversion allowing the transformation of map coordinates from a slew of map projection systems.
There are a number of ports that allow this tool to be seamlessly used programmatically. These include ports for python, R-Statistics, Proj4Net for dotNet, Javascript library. Through these options, the tool can be used directly from the command prompt or within code in scripts according to their preferred languages.

This tool simplifies coordinate transformation and is especially suited in automating the coordinate transformation for any area. By considering the Kenyan case, two systems have been dominant in their application. These are the Cassini-Soldner and the Universal Transverse Mercator (UTM) coordinate systems. By analyses of the UTM system used in Kenya (zones 36 & 37 both North and South) there is perfect agreement with Survey of Kenya computations, i.e. transformation from Geographic coordinates to UTM coordinates and vice versa.

Unfortunately, direct Proj4 computations of the Cassini Soldner are not consistent with the computations from Survey of Kenya (SoK). Geographic to Cassini-Soldner transformation indicate inconsistencies that aren’t easy to model as yet, though there are counter strategies to support that. A work around is the use of the famous Affine Transformation parameters that are currently used as a nation. At some point though it is expected that the Proj4 tool will be used instead supporting the C-S <=> geographic <=> UTM approach giving exact values. This will address the small discrepancies that arise from the application of transformation parameters.

David Kuria
About David Kuria 4 Articles
I'm passionate about GIS and related spatial technologies and their application in unraveling some of society's problems that have a spatial dimension.
  • Steve Ochieng

    Thanks David, this is very informative.