newbie needs help correcting distorted map

[Ed McNierney]

Mike -

Because MapServer supports projections defined parametrically (i.e. by specifying the family of projection and its parameters), it - practically speaking - supports any projection you want.  The European Petroleum Survey Group (EPSG) maintains a database of projections with a unique integer ID associated with each (the "EPSG code") and several products (including MapServer) support this "shorthand" way of describing projections.  "EPSG:4326" is EPSG code 4326, which is the "decimal degrees, WGS84 datum" projection.

If YOU don't know what projection you want, it's hard for any of us to know.  It sounds like you might be best served by just living with the "geographic" projection you're using for a while, until you better understand what you want.

Read the MapServer documentation to learn more about extents.  Normally, a MapServer request will include the extents (in the coordinates of the output map projection).

Finally, please ALWAYS reply to the group.  This allows others to participate in the discussion (the first person to answer your first question may not know the answers to all your questions), allows others to learn from the information so the question doesn't need to be asked again, puts the answers in the archives, and prevents the first person to reply from feeling like they've acquired a personal lifetime support commitment just because they answered one question <g>.

     - Ed

----- Original Message -----
From: Mike Jackson <mj at sci.fi>
To: Ed McNierney <ed at TOPOZONE.COM>
Sent: Tue, 12 Oct 2004 18:22:06 -0400
Subject: Re: [UMN_MAPSERVER-USERS] newbie needs help correcting distorted map


> Ed McNierney wrote:
> 
> >Mike -
> >
> >It sounds like nothing's wrong at all, except your choice of output projection.
>  The "geographic" projection has MANY limitations, including the fact that it
> badly distorts areas far from the Equator.  But all projections have strong
> points and weak points - that's why there are several to choose from.
> >
> >  
> >
> How do I tell which projection mapserver is using? Where is the list of 
> supported projections?
> 
> >You should try to do some research on what a good output projection would be. 
> If you're particularly interested in northern Europe, then look for the
> projections that are popular in those countries.  You can then change the
> MAP-level PROJECTION, UNITS, and EXTENT to reflect the *output* projection you
> want, while leaving the LAYER definitions alone, since those do accurately
> describe the *input* projection of your source data.
> >  
> >
> 
> I researched for a while and came up empty. Perhaps I don't know the 
> keywords to search for.
> 
> If a shapefile mentions an extent, then how can I know how to determine 
> an arbitrary extent that I would like to see? For example, what would 
> the extent be if I wanted to view Great Britain?
> 
> Thanks,
> Mike
> 
>