[mapserver-users] Extents and projections multiple datasets

[Paul Ramsey]

Gail,

The PROJECTION in each LAYER should be the projection of the *source
data*. So if your data is from multiple folks in multiple projections,
your LAYER projections should generally be different from one another,
not all the same.

The PROJECTION at the MAP level defines what you want your output
projection to be.  You can define your own, or you could pick
something standard that makes sense for your overall extent.  (If you
know what your overall extent is (statewide, coutrywide, global), I
can give you a suggestion.)

So, the LAYER projections are *input* projections, the MAP projection
is an *output* projection. By knowing both the input and output,
mapserver can apply a math transform to the data to project it on the
fly from the input to the output.

Yours,

Paul

On Fri, Apr 25, 2008 at 11:34 AM, Gail Long <codeburg at hotmail.com> wrote:
>
> I need some good pointers to docs or how-tos for working with extents and
> projections from multiple datasets.  I'm getting shape files from several
> different sources and they all seem to have different projections and built
> on lots of different extents.  I need to have them work together.
>
> I'm defining a projection for the map and the same projection in each layer
> definition of my map file:
>
>   PROJECTION
>     "proj=lcc"
>     "lon_0=90w"
>     "lat_0=45"
>   END
>
> I'm picking what I believe to be the largest extents.  Is this the right way
> to go?  I don't really understand how these go together.  I never have any
> trouble when the dataset is from one source.
>
> I would appreciate any advice.
>
> -- Things are only difficult while you don't understand them.
>
> ________________________________
> Back to work after baby– how do you know when you're ready?
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