Re: [mapserver-users] Beginner question - UK projections

[Frank Warmerdam <warmerdam@pobox.com>]

dchampion@clacks.gov.uk wrote:
> I'm a new Mapserver user, and not a geographer, so this may be a simple 
> question! Any help would be most gratefully received.
>
> I've compiled v3.5 with PROJ4 support and the demo works beautifully.
>
> I have a shapefile with data of my local area, Clackmannanshire in 
> Scotland. My problem is how to get this data to display. I'm fairly sure 
> it has something to do with projections, but that's where my understanding 
> runs dry.
>
> So, how do I determine:
>
> a) What extent values to use
> b) What values to put in the PROJECTION block in the .map file?
>
> I've taken EXTENT values from ArcView based on UK OS grid references, and 
> I've tried this for projection, based on my scant understanding, but no 
> data is displayed:
>
> PROJECTION
>   "proj=tmerc"
>   "ellps=airy"
>   "zone=31"
>   "north"
>   "no_defs"
> END

Daniel,

The UK National Grid should be represented as:

PROJECTION
  "proj=tmerc"
  "lat_0=49.000000000"
  "lon_0=-2.000000000"
  "k=0.999601"
  "x_0=400000.000"
  "y_0=-100000.000"
  "ellps=airy"
  "towgs84=375,-111,431,0,0,0,0"
END

The "towgs84" portion is only necessary if you will have data in other
datums.

Best regards,

--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent