[mapserver-users] Spherical Mercator Projection Problem

[Fawcett, David (MPCA)]

Sergey,

If your data is in epsg:4326 and you want to publish the data as epsg:3785, you will need to projection blocks to your layers.

Something like:

  PROJECTION
            "init=epsg:4326"
  END
The Projection block in the MAP section defines your output projection.  Because your data is not in the same projection, you will need to define a projection block in each layer section.  Those projection blocks define the 'input' projection.  They tell MapServer what projection the data exists in.  This allows MapServer (with proj4 support) to re-project your data to the output projection.

David.


From: mapserver-users-bounces at lists.osgeo.org [mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Sergey Kraev
Sent: Wednesday, February 23, 2011 5:01 AM
To: mapserver-users at lists.osgeo.org
Subject: [mapserver-users] Spherical Mercator Projection Problem

Hi,

I'm running MS4W v3.0 (including MapServer 5.6.5) on Windows.

My data source are PostGIS multipolygon countries' borders.

I have successfully got MapServer to render the world map in WGS84 projection using these settings:

Request:

http://127.0.0.1:8080/cgi-bin/mapserv.exe?map=world.map&mode=map&mapsize=256+256&mapext=-180+-90+180+90

world.map:

MAP
EXTENT                   -180 -90 180 90
  #EXTENT         -20037508 -20037508 20037508 20037508
  SIZE           256 256
  IMAGECOLOR     153 179 204
  FONTSET        "c:\MS4W\fonts\fonts.list"
  RESOLUTION        96
  MAXSIZE        5000

  PROJECTION
            "init=epsg:4326"
            #"init=epsg:3785"
  END
...
<layers don't have PROJECTION sections>

I would like MapServer to render the same data into a "Web (spherical) Mercator" projected map (epsg:3785), but I don't know how to modify my request and mapfile in order to get the correct map.

With the following settings I just receive a picture without any polygons.

\ms4w\proj\nad\epsg:

                 ...
<3785> +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs <>
...

Request (only mapext is different):

http://127.0.0.1:8080/cgi-bin/mapserv.exe?map=world.map&mode=map&mapsize=256+256&mapext=-20037508+-20037508+20037508+20037508<http://127.0.0.1:8080/cgi-bin/mapserv.exe?map=world.map&mode=map&mapsize=256+256&mapext=-180+-90+180+90>

world.map (only EXTENT and PROJECTION are different):

MAP
  #EXTENT                -180 -90 180 90
  EXTENT         -20037508 -20037508 20037508 20037508
  SIZE           256 256
  IMAGECOLOR     153 179 204
  FONTSET        "c:\MS4W\fonts\fonts.list"
  RESOLUTION        96
  MAXSIZE        5000

  PROJECTION
            #"init=epsg:4326"
            "init=epsg:3785"
  END
...
<layers don't have PROJECTION sections>

I'm assuming that -20037508 -20037508 20037508 20037508 is correct extent for the whole world map, since Google uses that and they also have Mercator projection.

Thanks for your help.

Sergey

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