OpenLayers/proj4js and the EPSG:27700 (UK) Projection

Question

I'm trying to use OpenLayers to transform projections, which in turn uses the http://proj4js.org/ library.

  var ll = new OpenLayers.Projection('EPSG:4326');
  var a = new OpenLayers.LonLat(3,53).transform(ll,new OpenLayers.Projection('EPSG:900913'));
  var b = new OpenLayers.LonLat(3,53).transform(ll,new OpenLayers.Projection('EPSG:27700'));

a will have transformed fine, b will not.

Is it possible to get support for EPSG:27700?

http://osgeo-org.1803224.n2.nabble.com/Reprojecting-Google-td1827338.html suggests adding in a extra class, but that's 2 years old so I'm hopeing it's improved since then.

Answer 1

did you include the proj4js files? By default OpenLayers only includes the transforms from 4326 to/from 900913 to save space. See http://trac.osgeo.org/openlayers/wiki/Documentation/Dev/proj4js for more details and other links on how to include the proj4s library.

Answer 2

proj4js javascript code actually goes out to http://spatialreference.org/ to get the info as a last resort (after looking for a local definition and a local JS file). But... http://spatialreference.org/ looks to be down right now. I haven't gone to it in a while so don't know when it went down or when it'll be back up.

However, a while back I grabbed most of the definitions from the website and this is it for 27700 and it matches @iant's post above

Proj4js.defs["EPSG:27700"] = "+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";

If anyone needs other definitions from spatialreference.org there's a zip file with 4000+ definitions available in this thread on OSGEO.