[OSM-talk] Coordinate transforms

Laurence Penney lists at lorp.org
Thu Apr 27 20:13:43 BST 2006


Thanks for that, Barry and Erik.

Since the accuracy is 7m (rather than 20cm), am I correct in thinking 
that none of these methods incorporate the bilinear interpolation based 
on the km square in which the point falls? Of course for GPS-related 
stuff that might not be considered too important, but it seems to me 
there's no point dropping accuracy if it's relatively easy to maintain it.

-- Laurence

Barry Hunter wrote:
> There is links to various PHP/Perl/JS code here:
> http://www.nearby.org.uk/downloads.html#programs
> nearly all converted from the gps.gov.uk information.
> These use the Hermert Transformation, with a typical accuracy of about 
> 7m I believe for most of GB. Irish gets better at about 2m.
> 
> For an online batch converter checkout
> www.osconverter.co.uk
> uses the definitive OSTN02 transformation.
> Or the one at www.gps.gov.uk (no longer requires you to login)
> 
> 
> I don't think there are any issues of IP after conversion. However 
> technically any coordinates in OSGB36 could be an issue as there is some 
> debate if the BNG is itself copyrighted, but as its just a means of 
> specifying a position its a real world fact. (A database of points could 
> be copywrited as that is a 'work', as such its the database of postcodes 
> that copywrited not the individual postcodes)
> 
> Hope that helps
> 
> Barry
> - www.nearby.org.uk - www.geograph.org.uk - www.trigtools.co.uk -






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