I'm looking for a Java-based solution to convert coordinates from Lambert93 to WGS84.
However, when testing it with data from North of France, the resulting longitude is off by something like 50km. Here's an example:
- Source data (in Lambert93): X = 668832.5384, Y = 6950138.7285
- Geofree conversion to WGS84: lat = 49.64961, lng = 2.56865 (this is correct)
- Output of the above Java program: lat = 49.65262, lng = 1.90503 (this is incorrect)
As far as I can tell, the program is "faithful" in that it faithfully implements the algorithms from IGN; so the fault either lies in the algorithms themselves, or in some parameter or some constant that needs to be adjusted.
How can one sort this out?
(There are other Java-based solutions capable of doing all sorts of GIS manipulations, but since I only need to do this conversion (on lots of data), I'd rather use a very simple, very light package, and "lambert-java" fits this bill nicely; however of course it also needs to be correct...)
Edit 2014-03: this was solved by the original author five months ago and has been working wonderfully ever since.