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

[Paul Kelly]

On Thu, 28 Oct 2010, Markus Hetzmannseder wrote:

> On Thu, 28 Oct 2010, Jean-Claude Repetto wrote:
>
>> I get the same results as geoland.at :
>>
>>  cs2cs +init=epsg:4326 +to +proj=lcc +lat_1=49 +lat_2=46 +lat_0=47.5
>> +lon_0=13.33333333333333 +x_0=400000 +y_0=400000 +ellps=bessel
>> +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +units=m +no_defs
>> 14.2833092 48.3098392
>> 470507.17	490503.01 -45.92
>> 16.371345 48.211996
>> 625724.58	483601.74 -44.45
>> 9.747076 47.503042
>> 130056.92	406637.21 -48.36
>
> Oh thx a lot, i did it that way, to get the wrong results:
> proj +proj=lcc +lat_1=49 +lat_2=46 +lat_0=47.5 +lon_0=13.33333333333333
> +x_0=400000 +y_0=400000 +ellps=bessel
> +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +units=m +no_defs
>
> And its looking like that josm-plogin is doing the same. Now i know at
> least how to generate the real projektion with the proj-toolbox itself.
> Now the plugin should be able to be changed in a similar way to use the
> cs2cs arguments.

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.

Best regards

Paul Kelly