[mapserver-users] Beginner question - UK projections

[Frank Warmerdam]

dchampion at 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,

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