[postgis-users] SRID tranformations (OSGB 1936)

[Mark Cave-Ayland]

Vyron Antoniou wrote:
> Hi,
> 
> I think I'm missing something with SRIDs and transformations but I don't
> really know what!!!
> 
> I have some POIs in WGS84 [ex. SRID=4326;POINT(-1.78103 51.09168)].
> 
> When I transform them into "OSGB 1936 / British National Grid" I use the
> function: Transform(the_geom,27700) so the result for the above point is :
> SRID=27700;POINT(415333.48161197 132490.68798396).
> 
> BUT.... if I use the transformation tool at
> http://www.geograph.org.uk/latlong.php the result is:
> 
> [WGS84: 51:5.5008N 1:46.8618W]
> Datum: Ordnance Survey Great Britain 1936
> Easting/Northing: 415431,132508
> 
> Running some test with GIS software it seems that the latter is the
> correct transformation
> 
> Any ideas?
> 
> Cheers!
> Vyron


Hi Vyron,

The definition of UK SRID 27700 is currently wrong since it is missing 
the OSGB36 datum definition. Unfortunately it only works correctly if 
you are using PROJ >= 4.5, but if this is the case then simply append 
"+datum=OSGB36" to the proj4text field and try again.


HTH,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
T: +44 870 608 0063