[Mapserver-users] Definition Projections, raw proj parameters vs EPSG code

[Jean-Francois.Doyon at CCRS.NRCan.gc.ca]

Hello,

I was wondering about the whole PROJ handling in MapServer. More precisely,
whether PROJ/MapServer does revers lookups on the EPSG list.

For instance, there is a fake EPSG code out there (cubewerx software users
will be familiar with this) that is EPSG:42304.

Now it turns out that that is the exact projection of our data.

So, when defining the projection of a layer in a MapFile used for WMS (or
WFS I guess), am I better off using the EPSG code, or a full definition ?
does it matter ?

In the case where the output projection is the same as the input, is there
an advantage to defining the layer using the EPSG code (MapServer is smart
enough to recognize no reprojection is needed, since the EPSG code for both
ends is the same), or does it reproject anyways? What if the layer defines
the projection using full PROJ.4 parameters, does MapServer recognize it as
being that same EPSG code projection, and skip the re-projection, or does it
reproject anyways (to the same projection)?

I'm guessing specifying projections with the EPSG code everywhere possible
is more efficient, but I want to check before I have to go and edit a bunch
of layers.

Thanks,

Jean-François Doyon
Internet Service Development and Systems Support / Soutien de systèmes et
developement de services Internet
GeoAccess Division / Division GéoAccès
Canada Center for Remote Sensing / Centre canadien de télédétection
Natural Resources Canada /  Ressources naturelles Canada
Phone / Téléphone: (613) 992-4902
Fax / Télécopieur: (613) 947-2410
http://atlas.gc.ca