PROJ.4 is a cartographic projections library written in C, originally written by Gerald Evenden (at that time at the USGS). It is in active use by quite a lot of applications, like QuantumGIS [L1 ], GRASS GIS [L2 ], MapServer, PostGIS, and many others.
More information can be found here: http://trac.osgeo.org/proj/
TR (2010-06-10) It turned out, that making a Tcl binding to proj.4 was quite simple. It just took a few days to get all things right. There is a more or less well-defined API [L3 ], that can be used and what I am currently coming up with is a new Tcl package with the main command proj::project. It works like this:
package require tclproj
# give an input coordinate system in proj.4 format,
# an output coordinate system,
# and a list of x/y coordinate pairs in a list:
proj::project "+proj=latlong +ellps=clrk66" "+proj=merc +ellps=clrk66 +lat_ts=33" {-16 20.25}
-1495284.21147 1920596.78992
proj::project "+proj=latlong +ellps=WGS84" "+proj=merc +ellps=WGS84 +lat_ts=33" {-16 20.25 10.33 54.55 9.23433 55.01132}
-1495251.43594 1920692.42348 965371.708328 6078165.01069 862977.824527 6152753.87339As of now, there is basic error checking, and some other commands already, but the heart is the proj::project command. The extension can be built with the proj.4 library statically linked in, so there is no need of seperately installing proj.4 on your system. My test system is a Mac right now, but my build script should also work nicely on Unix. I don't about Windows yet.
It would be fairly easy to also add commands that correspond to the ones used in the tcllib module mapproj.
If there is an interest for this work within the Tcl community, I can try to set up a place where you can download the source and maybe some binaries ... just drop me a line.
Related topics: geodesy