How to convert latitude/longitude in degrees to BBOX where SRS=EPSG:27700

Anyone know how to convert latitude, longitude in degrees to define a BBOX where SRS=EPSG:27700?

I am trying to call a WMS service with a URL like following (not a real link): http://mysecretmappingserver.com/wms?user=myuser&pwd=mypassword&VERSION=1.1.1&REQUEST=GetMap&LAYERS=ap25cm&STYLES=&SRS=EPSG:27700&BBOX=229096,231675,229296,231875&width=400&height=400

~~Any language would be fine; C# preferable.~~

Spacedman has been trying to help me, but I can't seem to get Proj4Net to work for me - all me, I'm sure - but if someone knows either Proj4Net or the math involved, that might be better...

Solution

You need an interface to the PROJ.4 projections library in your language of choice. In R, for example, its in the rgdal package:

Here's some points (1,1 to 2,2 degrees) in epsg:4326:

> pts
SpatialPoints:
     coords.x1 coords.x2
[1,]         1         1
[2,]         2         2
Coordinate Reference System (CRS) arguments: +init=epsg:4326

and voila:

> spTransform(pts,CRS("+init=epsg:27700"))
SpatialPoints:
     coords.x1 coords.x2
[1,]  734005.9  -5416918
[2,]  845270.7  -5305999
Coordinate Reference System (CRS) arguments: +init=epsg:27700

Proj.4 docs here:

http://trac.osgeo.org/proj/

Since this is OSGB, probably a better example would be in the UK: here's a point in central london:

> pts = SpatialPoints(cbind(-0.109863,51.460852),proj4string=CRS("+init=epsg:4326"))
> spTransform(pts,CRS("+init=epsg:27700"))SpatialPoints:
     coords.x1 coords.x2
[1,]  531407.1  175235.8
Coordinate Reference System (CRS) arguments: +init=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
+towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894