On 2013-01-09 16:13, Johnny wrote:
Are you aware of any way to batch process this in Linux to enable swift
conversion of multiple references?
You'd need a script that maps the 2-letter grid cell identifiers to the
respective offsets, then calculates the Easting and Northing values. I
can send you an example off-list.
Please note that behind the scenes, these datum shift parameters are
applied: +towgs84=375,-111,431,0,0,0,0 (which might be what you want
.. or not).
Sorry, I don't know much about cartography and datums, but guess these
are the defaults by gdaltransform? Anyhow, it achieves what I want! :)
Indeed, these are the default values for a 3-parameter transformation
(I'm using GDAL 1.9.2).
On page 33 of [1], OSGB gives the values for a 7-parameter
transformation which should be more accurate in most cases. You have to
revert the signs of the given values and use them like this:
+towgs84=446.448,-125.157,542.06,0.1502,0.247,0.8421,-20.4894
And there is OSGB's grid shift file at [2] which leads to even more
accurate results.
Hermann
[1]
http://www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf
[2]
http://www.ordnancesurvey.co.uk/oswebsite/gps/osnetfreeservices/furtherinfo/ostn02_ntv2.html
Regards,
Johnny
Footnotes:
[1]
http://digimap.edina.ac.uk/webhelp/os/gazetteer_plus/grid_ref_conversion.htm
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