[Proj] OSGB36

[Roger Oberholtzer]

On Fri, 2006-01-13 at 14:19 +0100, Oscar van Vlijmen wrote:
> > From: Paul Kelly <paul-grass-stjohnspoint.co.uk>
> > Subject: Re: [Proj] OSGB36
> > On Thu, 12 Jan 2006, Roger Oberholtzer wrote:
> 
> >> This time, I am testing OSGB36 (UK). My current method uses geotrans. I
> >> am using a 7 parameter transform (in geotrans-speak).
> >> A sample set of points:
> >> WGS84 (somewhere near Norwich):
> >> lat=52.63820000
> >> lng=1.25423000
> >> I should get (UK TRL say):
> >> N=620282.88  E=309469.17
> 
> > You need to do a datum transformation (WGS84 to OSGB36)
> > With the following command line
> > cs2cs +proj=latlong +ellps=WGS84 +towgs84=0,0,0 +nodefs +to +proj=tmerc
> > +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy
> > +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894 +units=m
> > +no_defs
> > I get these results
> > 620286.26       309466.38
> > for your test point. Much closer.
> 
> I can confirm the test results from mr. Kelly.
> A more verbose description:
> Transformation from WGS84 to OSGB36:
> lat=52.63820; lon=1.25423; h=0;
> This gives:
> lat=52.637798, lon=1.256045, h=-45.3413
> Transformation parameters:
> dx=-446.448; dy=125.157; dz=-542.060;
> rx=-0.1502; ry=-0.2470; rz=-0.8421; ds=20.4894;
> Position vector rotation, approximate transform (like PROJ.4 does).
> Transverse Mercator on Airy 1830 ellipsoid:
> with: lat0=49.0; lon0=-2.0; x0=400000; y0=-100000; k0=0.9996012717;
> gives: x=620286.2515, y=309466.3864
> 
> Source of the parameters:
> "A guide to coordinate systems in Great Britain", Ordnance Survey, v1.4 May
> 2002
> <http://www.gps.gov.uk/additionalInfo/images/A_guide_to_coord.pdf>
> 
> Differences with Ordance Survey results must be attributed to lack of
> gridinterpolation.

Is that the main thing that OSTN02 adds to all this?

-- 
Roger Oberholtzer
OPQ Systems AB