[mapserver-users] Re: Trouble with South pole projection issues

[Frank Warmerdam]

On Fri, Jan 20, 2012 at 11:51 AM, Fuchs Juan Carlos <
jfuch at indec.mecon.gov.ar> wrote:

> ** **
>
> Hi Mr Frank Warmerdam****
>
> I sent out this post, but no one answer, so I´m here, bothering you again.
> ****
>
> Any adwise would gratefull received!****
>
> Happy New Year!****
>
> Juan Carlos Fuchs, from ****Argentina****.
>


> ...
>


> This is the *.prj from the shp i have, and need to bring along with the
> other one.****
>
> ** **
>
>
> PROJCS["lambert",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["False_Easting",10000000.0],PARAMETER["False_Northing",6391246.5],PARAMETER["Central_Meridian",-60.0],PARAMETER["Latitude_Of_Origin",-40.0],UNIT["Meter",1.0]]
> ****
>
> ** **
>
> that is my first try so far,: from my *.map file layer (Projection)****
>
> ** **
>
>             PROJECTION****
>
>                         "proj=laea"****
>
>                         "ellps=WGS84"****
>
>                         "lat_1=40"****
>
>                         "lon_0=-60"****
>
>                         "south"****
>
>             END****
>
>
> ...


> As you can see it goes LL EPSG:4326 in geographics (????) is there some
> doc I can read about the "towgs84" Parameters, my guess is that they have
> not to be 0,0,0,0,0,0,0....****
>
>
>
Juan,

I do not believe the problem is related to the +towgs84 datum shifting.  I
believe the problem is that your LAEA projection definition for MapServer
lacks the false easting and northing values.  Try something like:


PROJECTION

   "+proj=laea +ellps=WGS84 +lat_1=40 +lon_0=-60 +south +x_0=10000000.0
+y_0=6391246.5"

END


The key change here being the addition of +x_0 and +y_0.  I am not familiar
with the

+south parameter for LAEA though it might be appropriate.

By the way, you can use the new gdalsrsinfo utility to translate coordinate
systems with GDAL.  eg.

warmerdam at gdal:~$ gdalsrsinfo
ESRI::'PROJCS["lambert",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["False_Easting",10000000.0],PARAMETER["False_Northing",6391246.5],PARAMETER["Central_Meridian",-60.0],PARAMETER["Latitude_Of_Origin",-40.0],UNIT["Meter",1.0]]'

PROJ.4 : '+proj=laea +lat_0=-40 +lon_0=-60 +x_0=10000000 +y_0=6391246.5
+datum=WGS84 +units=m +no_defs '

OGC WKT :
PROJCS["lambert",
    GEOGCS["GCS_WGS_1984",
        DATUM["WGS_1984",
            SPHEROID["WGS_84",6378137.0,298.257223563]],
        PRIMEM["Greenwich",0.0],
        UNIT["Degree",0.0174532925199433]],
    PROJECTION["Lambert_Azimuthal_Equal_Area"],
    PARAMETER["False_Easting",10000000.0],
    PARAMETER["False_Northing",6391246.5],
    PARAMETER["longitude_of_center",-60.0],
    PARAMETER["latitude_of_center",-40.0],
    UNIT["Meter",1.0]]

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 Software Developer
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