[Proj] U.K. OSTN02 and OSGM02
paul-grass at stjohnspoint.co.uk
Mon Dec 19 10:26:07 EST 2005
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
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.
Sorry I haven't really been any help.
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