[gdal-dev] Problem with +ellps=airy which is used for BNG

[Jean-Claude REPETTO]

Andreas Joisten a écrit :
> Hi all,
> 
> The BNG (British Natial Grid) based on the airy Ellipsoid but GDAL did not know this parameter.
> 
> 
> +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs 
> 
> Probably, gdal does not know this parameter:  +ellps=airy

Hello,

You don't need to specify the ellipsoid, because it is already contained 
in the datum definition :

proj -v +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 
+y_0=-100000 +datum=OSGB36 +units=m +no_defs
#Transverse Mercator
#	Cyl, Sph&Ell
# +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
# +datum=OSGB36 +units=m +no_defs +ellps=airy
# +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894

Jean-Claude