Projection WGS84 in decimal degree

[Ed McNierney]

Frank & FP -

Good catch, Frank - that's an excellent possibility.

FP, make sure your EPSG file contains an accurate definition of <27582>,
including the prime meridian (primem) of 2.337229166666667.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: fwarmerdam at gmail.com [mailto:fwarmerdam at gmail.com] On Behalf Of
Frank Warmerdam
Sent: Wednesday, January 11, 2006 10:16 AM
To: Ed McNierney
Cc: MAPSERVER-USERS at lists.umn.edu
Subject: Re: [UMN_MAPSERVER-USERS] Projection WGS84 in decimal degree

On 1/11/06, Ed McNierney <ed at topozone.com> wrote:
>
> FP -
>
> Your first GPS layer definition should be fine.  You don't say what 
> data source you are using for your GPS data, but if it is a shapefile 
> or inline features you will be using decimal degrees and those will 
> work fine with the "init=epsg:4326" definition.
>
> The first thing I would suggest is that you confirm that the 
> EPSG:27582 projection is in fact correct. The related Paris / Lambert 
> projections (27581-27584, for example) are all rather similar and can 
> certainly look the same.  Can you check the coordinates of a few 
> points to make sure they're accurate?  An error of 200km is far too 
> large to be a datum error, but could easily be due to the different 
> false easting/northing values used in these similar projections.

FP,

I would add to Ed's comments that the PROJ definitions files for EPSG
zones with alternate prime meridians are often messed up, and a
horizontal offset of 250km is approximately the distance of the paris
meridian from greenwich.

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