Projection LAMBERT III (South of France) parameters

[Homme Zwaagstra]

On Thu, Jul 07, 2005 at 09:46:13AM -0400, Frank Warmerdam wrote:
> On 7/7/05, Selim Hernandez <pimpoumvlan at hotmail.com> wrote:
> > Hello,
> > 
> > I can't find the right PROJECTION object's parameters in my .map file for
> > coords in LAMBERT III (used for the South of France).
> > 
> > Though, when I translate these coords into the WGS 84 system (epsg:4326),
> > it works fine.
> > 
> > Maybe the coords in the epsg file are wrong.
> > 
> > I used the following parameters and none of them worked :
> > 
> > "proj=lcc"
> > "lat_1=44.10000000000001"
> > "lat_0=44.10000000000001"
> > "lon_0=2.33722917"
> > "k_0=0.999877499"
> > "x_0=600000"
> > "y_0=200000"
> > "a=6378249.2"
> > "b=635651"
> > "pm=paris"
> > "units=m"
> 
> Selim,
> 
> There is an issue with the automated conversion from EPSG into 
> PROJ.4 syntax for coordinate system using gradians for angular
> values.  I think the angular->degree translation is happening twice.
> 
> Could you try using lat_0=49 and lat_1=49? 
> 
> Alternatively, it might be that the prime meridian is being improperly
> applied.  If so, try setting lon_0=0.  
> 
> I do appologise for this botching of some complex coordinate systems.
> I have had some open bug reports on it for some time, but haven't gotten
> back to deal with it properly.
> 
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent

The PROJ.4 syntax that we use for Lambert III is:

+proj=lcc +lat_1=44 +lat_2=49 +lat_0=46.5 +lon_0=3 +x_0=700000 +y_0=6600000 +ellps=GRS80 +units=m +no_defs no_defs

The parameters are the result of trawling through various
literature. I don't profess to be an expert in projections, but this
seems to transform data in Lambert III satisfactorily for use in our
mapserver apps. For convenience we added it into the PROJ.4 epsg file
with the id 102110.

I hope this helps!

Kind regards,

Homme Zwaagstra.