Re: [UMN_MAPSERVER-USERS] Projection WGS84 in decimal degree

[Ed McNierney]

Title: Projection WGS84 in decimal degree

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.

 

     - Ed

 

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

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From: UMN MapServer Users List [mailto:[EMAIL PROTECTED] On Behalf Of zze-SIGALE PORTANERI F ext RD-BIZZ-SOP
Sent: Wednesday, January 11, 2006 7:20 AM
To: MAPSERVER-USERS@LISTS.UMN.EDU
Subject: [UMN_MAPSERVER-USERS] Projection WGS84 in decimal degree

Hi all,

I have a set of WGS84 data points that come from GPS system in decimal degree longitude/latitude coordinates.
I would like to display them with mapserver using a mapfile which already define several layers in Lambert II.

I did specified the global projection in the mapfile for Lambert II etendu :

PROJECTION
"init=epsg:27582"
END

The GPS LAYER describing the WGS84 data includes the projection definition for the WGS84 :
LAYER
  NAME "GPS"
  PROJECTION
    "init=epsg:4326"
  END
  ...
END
But points are not displayed at the right place (at about 200km far away)  :-(
Apparently, the 4326 epsg definition considers longitude/latitude coordinates in Degree/Minute/Second, while my data are in Decimal Degrees.

So I tried to specify the following in the GPS layer :

PROJECTION
"proj=longlat"
"ellps=WGS84"
"datum=WGS84"
"units=dd"
END


but mapserver returns: "Error in msProcessProjection(): unknown unit conversion id"
The prog -lu command doesn't list the "dd" unit...
How to display longlat data in Decimal Degree under Mapserver?

Regards
FP