HarryS
Posts: 1
Joined: Wed May 18, 2011 6:24 pm
Contact: Website

bug with OSGB36 definitions?

Wed May 18, 2011 6:37 pm

Hi,

I'm transforming between OSGB36(British National Grid) and UTM Zone 31N(European 1950).
If I select OSGB36 grid from Earth-Europe-United Kingdom-OSGB36-British National Grid, I get a different result from selecting OSGB36 from Earth-Europe-United Kingdom-England-OSGB36-British National Grid. The difference is about 6 metres.

Also, If I transform from OSGB36 to ETRS89 using the British Ordnance Survey software (Grid Inquest), I get a different result from CoordTrans.

How can I reliably transform from ETRS89-OSGB36-UTM Zone 31N(European 1950).

Many thanks for your help

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johan
GpsGate
Posts: 14387
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: bug with OSGB36 definitions?

Wed May 18, 2011 6:53 pm

Datums before 1970, when laser was introduced for geo-measurements are less reliable. Older is less reliable. OSGB is from 1936.

CoordTrans uses 7 parameter Helmert for datum transformation. And no correction tables are used.

Regards,
Johan

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