[mapserver-users] PostGIS data in EPSG:31300 using for Google Maps overlay

[Steven De Vriendt]

Brent,

Very, very usefull info. Thanks.  I was just about to reprojecting my data :-)
I thought the SRID table was "constrained" to the geometry and you couldn't
change it. Seems like that's why the 'virtual' table is there for. Ok,
well, I'll give
it a try. Thanks for your input !

Regards,
Steven

On Tue, Apr 8, 2008 at 7:58 PM, Brent Wood <pcreso at pcreso.com> wrote:
>
>  --- Steven De Vriendt <gisaalter at gmail.com> wrote:
>
>  > Hi list,
>  >
>  > I have some data in PostGIS I wish to overlay in Google Maps using WMS
>  > I'm using the same data in a mapserver application, where EPSG code
>  > 31300 is used.
>  > Now for overlay in Google Maps, 4326 is required.
>  > I have made a copy of my map-file and specified 4326 as projection
>  > system.Yet, non of my data is showing up.
>  >
>  > Do I need to reproject my data for this use ? I thought PostGIS was
>  > capable of doing reprojection on the fly ?
>
>  Hi Steven,
>
>  Both mapserver & POstGIS can reproject the data on the fly, but they need to be
>  told the input & output projections.
>
>  As your data is all displayed via mapserver, the instructions either way will
>  be in your mapfile.
>
>  To reproject using PostGIS, edit the SQL command in your data statement which
>  retrieves the PostGIS data. You need to tell PostGIS to return a virtual table
>  to mapserver, and transform the data to the required projection in this. Edit
>  the data line in the layer something like this:
>
>  DATA "new_geom from (select gid, transform(the_geom,4326) as new_geom from
>  table) as mytable using unique gid using srid=4326"
>
>
>  To reproject in mapserver, you need to set the main mapfile projection to
>  EPSG:4326, using, in the global header part of the mapfile:
>
>  UNITS DD
>  PROJECTION
>   "init=epsg:4326"
>  END
>
>  In the METADATA section, you'll need to set the output projection for WMS, eg:
>  METADATA
>   "wms_title" "My WMS Server"
>   "wms_srs"   "EPSG:4326"
>  END
>
>  Then in the layer definition, you specify the layer's native projection, so
>  mapserver can reproject from one to the other:
>
>  LAYER
>   ...
>   PROJECTION
>     "init=epsg:31300"
>   END
>   ...
>  END
>
>  Note that to reproject in PostGIS, Proj.4 support must be compiled into
>  PostGIS, and similarly for mapserver if you do the reprojection there. If you
>  compiled these from source, this is not done by default, & you'll need to run
>  configure with the appropriate flag. If you installed from a package, or on
>  Windows, proj support is generally built in.
>
>
>  HTH,
>
>   Brent Wood
>