geographical accuracy

[Bob Walker]

On Wed, 21 Feb 2007, Graham Seaman wrote:

> Hi all,
>
> I'm trying to generate a set of latitude/longitude points for use with google 
> maps (to avoid having to query google for the actual locations). What I have 
> as source data is a set of northing/easting values with 6 digits for 
> northing, 6 digits for easting. I'm using Geography::NationalGrid::GB to 
> convert these to lat/long pairs. The results are all approximately correct, 
> but generally about 20 metres or so off in an apparently random way. The 
> features I'm trying to locate are mostly quite large and clearly visible on 
> google's satellite/hybrid view (but I have around 20,000 locations to deal 
> with, so can't correct them all manually). I have seen the same features 
> located accurately on another google map application, so I know the problem 
> is not at the google end of things.
>

its the ellipisoid.
http://search.cpan.org/~mysociety/Geo-HelmertTransform-1.11/lib/Geo/HelmertTransform.pm
will help you.

-- 
Bob Walker
http://www.randomness.org.uk/
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