Dear all
Can anyone help me with a problem involving Ordnance Survey coordinates,
MapInfo's conversion to Lat/Long and discrepancies with GPS-output ?
Basically the problem is:
a) We've used MapInfo to derive Lat/Longs from OS-coordinates
b) These coordinates don't match what the client's GPS says
c) The GPS matches (nearly) to a transformation done by a 3rd party.
To give an example for OS coordinates 504469,247557 (middle of England):
MapInfo Lat/Long = -0.474, 52.116
GPS = -0.287, 52.070
Client's database = -0.294, 52.133
Independent 3rd-party = -0.283, 52.066
I know about the accuracy constraints applied to 'non-military' GPS but as the
MapInfo value is so anomalous this is not the issue.
To do the MapInfo 'conversion' I've used MI4.5 and simple done:
Table->Create Points
Projection ... British National Grid
Select CentroidX(obj), CentroidY(obj) ......
Have I used MapInfo correctly ?
Is it's computation of projections correct ?
Could the other sources be incorrect ... and how/why ?
I don't actually know much about projections (it may well be obvious from the
above !) and I've only rejoined the list recently so if the answer is obvious (or has
been covered elsewhere) my apologies for wasting time ... but please point me to
such a solution !
Regards
James
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