[Proj] OSGB36

Roger Oberholtzer roger at opq.se
Fri Jan 13 11:02:45 EST 2006

On Fri, 2006-01-13 at 11:28 -0400, John Smart wrote:
> >> Differences with Ordance Survey results must be attributed to lack of
> >> gridinterpolation.
> >
> > Is that the main thing that OSTN02 adds to all this?
> >
> OSTN02 is a grid-shifts file with grid resolution = 1km. The shifts are from 
> GB National Grid (i.e. a TM projection) on ETRS89 to the same projection on 
> OSGB36. Bilinear interpolation is used between grid nodes. The stated 
> accuracy is something like 0.1m at 1 sigma. The grid-shifts file has a nice 
> feature that it has dummy values outside of a 10km buffer around GB 
> coastline. The file also has orthometric height differences (OSGM02) at the 
> same grid points.
> The 7 parameter is stated as being good for applications needing accuracy 
> less good than +/- 5m.
> Could be nice if Proj would support this grid shift file, but what is really 
> needed (IMHO) is some standardization on such file formats so that a 
> plethora of different formats would not be needed. Ntv2 is something of a 
> standard but relates to lat/long differences not projection grid. 

As a start, where can one get the grid shift values? Is there only one
standard set?

Isn't there any Linux library that will do this (commercial is fine,

Roger Oberholtzer
OPQ Systems AB

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