[Mapserver-users] Reading in Projections from layer data files

[Pericles S. Nacionales]

Tyler, folks,

I probably shouldn't be the one replying to your message but I'm sure
Steve L., Frank W., and others will say something if I'm wrong...

MapServer doesn't really know projections.  If you don't define
projections, it's assumed that your input and output projections are the
same.  If you do define an output projection (and input projection),
MapServer will pass that info to the proj library which does the
reprojection.

So, don't define projections unless you have to (if you are implementing
WMS apps or just need on-the-fly reprojection because you have data in
different projections).  MapServer will probably create your maps faster
without it.

As for ESRI-style .PRJ file, MapServer doesn't know what that is and
doesn't use it (but perhaps gdal/ogr does).  The raster world file, or
the GeoTIFF projection info is used for extent information and not
projection.  It would be nice to have those projection info
automatically used by MapServer but not if performance suffers
considerably.

Anybody else have $0.02 to give away?

-Perry

On Mon, 2004-04-26 at 13:45, Tyler Mitchell wrote:
> Seems projections are the topic of the day.  It got me wondering, when 
> does (or does not) MapServer read and use projection info from the source 
> data files?  I.e. if I have my MAP projection set in the map file, and I 
> have a shape file with a prj (or tiff with tfw) - do I need to add a 
> PROJECTION section to my LAYER or not?  I guess, basically, I'm wondering 
> does mapserver ever reproject without layer projections being explicitly 
> defined? 
> 
> Tyler
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