[Proj] U.K. OSTN02 and OSGM02

[Roger Oberholtzer]

On Mon, 2005-12-19 at 15:26 +0000, Paul Kelly wrote:
> Hello Roger
> 
> On Mon, 19 Dec 2005, Roger Oberholtzer wrote:
> 
> > Is it possible to calculate the U.K.'s OSTN02 and OSGM02 X/Y coordinates
> > with proj?
> 
> OSGM02 is the geoid model that models the separation between the
> WGS84/ETRS89/GRS80 ellipsoid and the Airy ellipsoid used for Ordnance Survey
> heights (or the Modified Airy ellipsoid in the case of Northern Ireland, which
> OSGM02 is also supposed to apply to but didn't seem quite right when I tried
> it about two years ago). PROJ.4 can't make use of this information and it 
> would need to be applied to the WGS84 height separately from the 
> re-projection step.

I can skip the OSGM02 bit for now.

> OSTN02 is the transformation grid to convert Ordnance Survey National Grid 
> eastings and northings to/from ETRS89/WGS84/GRS80 latitude and longitude. It 
> would be possible to use this data with PROJ.4 by converting it into the 
> gsb format, which PROJ.4 recognises. I did something similar for the 
> national gridshift file used in France (see 
> http://www.stjohnspoint.co.uk/gis/france.htm although I have recently 
> recognised that this might contain a VERY small error due to slightly 
> different parameters used for the Clark 1880 ellipsoid as compared to the 
> parameters built into PROJ.4) and would like to do it for OSTN02 but 
> haven't had time.

I plan on starting with WGS84 latitude and longitude. I get the general
idea of what you did in the link above, but I am uncertain how to do
this for OSTN02.

> Sorry I haven't really been any help.

Well, a bit. At least the answer was not that I could not get there from
here. Not that I know the way...

-- 
Roger Oberholtzer
OPQ Systems AB