[ms4w-users] geographic projection converted to Mercator?

Frank Warmerdam warmerdam at pobox.com
Fri Jan 6 11:59:03 EST 2006

On 1/6/06, Tib Kat <oceatoon at gmail.com> wrote:
> Hi
> I'm a complete novice using MapServer still gettting familiar with the
> structure and what can and cannot be done.
> My client has Geographic Projection image and I'll need to have them
> served as Mercator Projection.
> Can MapServer do this sort of transformation ?
> is it more efficient to directly use Mercator removing the CPU Load of
> converting one format to the other.
>  is there a caching device so this is done only once ?
> If my original image is 10000x10000 and I need to be served 256x256
> tiles according to the viewing section is this also possible?


Image reprojection is fairly expensive to do on the fly in
MapServer, so if you know you always want to serve it in
Mercator it would be prudent to reproject it once ahead of

You will need to use a non-mapserver utility to do so.
One that will do it is the gdalwarp utility but I don't
imagine that is distributed in ms4w.   You can install
FWTools from http://fwtools.maptools.org and use it
from the FWTools Shell, something like:

  gdalwarp -s_srs WGS84 -t_srs "+proj=merc ..." in.tif out.tif

gdalwarp should understand the same PROJ.4 syntax used
by MapServer for projections (with a few caveats).

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

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