[OSM-dev] Code for OSTN02?

[TimSC]

Thomas Wood wrote:
> Good luck, this is the one projection that the OS actually sell for
> professional uses.
>
> I thought that OSTN02 wouldn't actually be needed unless for the very
> high precision stuff. The standard OSGB36 transform should be good
> enough otherwise?
I don't think they are that restrictive. They seem to have a freeware 
library and API for windows (closed source) here 
http://www.ordnancesurvey.co.uk/oswebsite/gps/osnetfreeservices/furtherinfo/questdeveloper.html

On accuracy, converting NR730100 to ETRS89,

OSTN02: 55.33149630, -5.58040715
Helmert (based on OS spreadsheet[1], ported to C++): 55.331258, -5.580440849
Nearby.org.uk:  55.331495, -5.580444
http://www.rutter.uklinux.net/ostowiki.html: 55.33149480 -5.58044426
Streetmap.co.uk: 55.331967, -5.579682
ganzc (by Chuck Gantz): 55.3314950512,-5.58040512526

[1] 
http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/ProjectionandTransformationCalculations.xls

First observation: there is a range of accuracies from various sources! 
ganzc was better than I remember. I will investigate that one further.

Tim