[OSM-talk] BNGR (was: Bringing OSM to walkers)

[OJW]

On Sunday 06 May 2007 20:45, Frederik Ramm wrote:
> How much of these design choices can one replicate without receiving
> love letters from OS attorneys?

All of them? it's just a 1km^2 grid and the metre is SI


As to the BNGR ("OSGB grid") thing, I noticed recently that the recommended 
way to convert from Ordnance Survey's grid system to WGS-84 is using a big 
datafile containing different conversions for every point in the UK.

http://gps.ordnancesurvey.co.uk/convert.asp

i.e. the Helmert transform gives "up to 5 metres inaccuracy", whereas the 
exact transform requires a data file and windows DLL.

..which might explain their allusions to the BNGR being copyrighted despite it 
dating from 1830 and 1936 -- do they refer to the Quest software and data 
file for OSTN02 conversion?