[Proj] truble to translate coordinates from WGS84 to EPSG:31287

[Markus Hetzmannseder]

On Thu, 28 Oct 2010, Paul Kelly wrote:

> On Thu, 28 Oct 2010, Markus Hetzmannseder wrote:
>
>
> The proj command does a simple forward projection and ignores the +towgs84
> datum transformation parameters. The cs2cs command takes these into
> account to give a more accurate result. If you leave off the +towgs84
> parameters from the cs2cs command line you will get the same result as
> with the proj command line. It looks to me like the JOSM plugin is not
> doing the datum transformation, only the projection (I had a quick glance at
> <http://svn.openstreetmap.org/applications/editors/josm/plugins/epsg31287/src/com/jhlabs/map/proj/LambertConformalConicProjection.java>)
> to confirm this) - but that is certainly not easy to fix.

Jeah, i know, i was coming to the same result myself too. The epsg31287 
plugin is using the jhlabs java lib to do all the transformation. And on 
the the jhlabs site i found under "What is missing" the statement 
"Coordinate system and geodetic datum conversion is missing." 
(http://www.jhlabs.com/java/maps/proj/index.html)

Doing the transformation with the jhlabs-lib would require some additional 
coding for the datum transformation. Something i am not able to do with my 
tiny knowlege in both fields, java and the math behind all that 
transformations.

Another way would be to rewrite the plugin with another calculation lib in 
behind. Maybe something from http://geotools.org/ could help...

At least we know now where that offset of the current epsg31287 plugin is 
coming from. I hope it will help the author of the plugin a bit to find a 
solution.

Markus