Thanks for the link Barry.... just integrated it with some postcode data I have, and it appears to work very well!
Paul
On 16/06/05, 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
>
>
>
