Thanks! Matt
On 6/16/05, Barry Hunter <[EMAIL PROTECTED]> wrote: > I can't really say much on the accuracy of the easting/northing to lat/long > conversion, but it seems quite accurate and appears to be reversible > (converting backwards and forwards doesn't introduce 'drift') - in one > direction the iterative process is used. > > However the conversion between osgb36 and wgs84 lat/long uses the Hermert > Datum Transformation. This is typically accurate to about 7 meters across > the GB mainland. If interested can dig out maps detailing the drift. > > There is roughly equivalent to that as performed in a GPSr but gives > slightly different results. (being optimised for small cpu usage) > > There is a more detailed Datum transformation available from the OS, which > promises sub cm accuracy but this is huge and cumbersome, involving a large > lookup table. > > Hope that helps, > > Barry > > > ----- Original Message ----- > From: "Matthew Hurst" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Thursday, June 16, 2005 6:23 PM > Subject: Re: [backstage] Converting between easting/northing and long/lat > > > > This is great - I have been looking for exactly the same thing to deal > > with UK data. > > Can you comment on the accuracy of the conversion? My understanding is > > that > > the operation (at least as described in OS literature) is an iterative > > one, so precision may > > well be dependant on cpu time. > > > > MattH > > > > On 6/16/05, Barry Hunter <[EMAIL PROTECTED]> wrote: > >> > >> I have recently got some code working for geograph.co.uk project. > >> > >> It's not polished yet, but does work: > >> http://cvs.sourceforge.net/viewcvs.py/geograph/geograph/libs/geograph/conversionslatlong.class.php?rev=1.1&sortby=date&view=log > >> > >> (you will just need to change the class definition to remove the 'extends > >> Conversions' which it doesn't need to function) > >> > >> then can just be used: > >> > >> $conv = new ConversionsLatLong(); > >> list($e,$n) = $conv->wgs84_to_osgb36($lat,$long); > >> list($lat,$long) = $conv->osgb36_to_wgs84($e,$n); > >> > >> there is a utility function to convert easting/northing to grid reference > >> but not the other way yet! (osgb36_to_gridref) > >> > >> Barry > >> > >> > >> ----- Original Message ----- > >> From: Paul Maunders > >> To: [email protected] > >> Sent: Tuesday, June 14, 2005 8:05 PM > >> Subject: [backstage] Converting between easting/northing and long/lat > >> > >> > >> Hi Guys, > >> > >> On the subject of maps, I was wondering if anyone has any php code to > >> convert between OS grid references or GB OS easting / northings and > >> longitude and lattitudes? > >> > >> Regards, > >> > >> Paul Maunders > > > > > > > > >
