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