7m error often associated with the approx. transformation that consumer grade gps units (or many of the coordinate conversion websites) carry out compared to the full OSTN02 definitive transformation. If possible should always use the OSTN02 transformation.
Below are a few examples of points in wgs84 and osgb format transformed with OSTN02 if you want to check some others Point ID Latitude Longitude Ellipsoid Height Northing Easting Orth. height Time RTCM-Ref 0000 52.0242012 -0.7717783 139.488 236908.8906 484368.9928 92.26152 31/05/2011 14:44 RTCM-Ref 0014 51.9015014 -0.1784953 158.652 224117.4848 525415.3853 112.47864 31/05/2011 14:38 RTCM-Ref 0019 52.25181 -2.19794 87.084 261532.2794 386583.8284 37.4539 14/06/2010 09:30 1 52.0652051 -2.6857082 99.02443 240980.03 353090 48.15 13/04/2012 15:16 -----Original Message----- From: Nick Hopton [mailto:[email protected]] Sent: 10 May 2012 11:13 To: [email protected] Subject: [Qgis-user] OSGB coordinates to WGS84 lat/lon problem A chap on QGIS at Stack Exchange is having problems with accuracy when transforming from Ordnance Survey grid coordinates to WGS84 lat/lon. He's finding discrepancies in the order of seven metres. Using QGIS 1.7.4, OSGEO4W under Vista I was able to reproduce the problem, but using QGIS Lisboa RC1 under Ubuntu 11.10 produced transformations good to better than a metre. My first reaction was that there must problems with the QGIS 1.7.4 Proj4 parameter string for EPSG:27700, but on checking I found that 1.7.4 and Lisboa use identical strings for this CRS. I'm now at a bit of a loss to understand how following an identical procedure on both systems can produce differing results. If anyone would care to check this, below is the csv file I used for my tests. Station,x,y Inkpen,437346.0,161624.8 Hodmore,468296.3,178184.9 Hindhead,489984.6,135909.7 Under Ubuntu these coordinates transformed to: Inkpen 437346 161624.8 -1.465102 51.352478 Hodmore 468296.3 178184.9 -1.017527 51.498487 Hindhead 489984.6 135909.7 -0.715814 51.115423 Under Vista they transformed to: Inkpen 437346 161624.8 -1.46511 51.352424 Hodmore 468296.3 178184.9 -1.017525 51.498435 Hindhead 489984.6 135909.7 -0.715808 51.115362 In my part of the world the differences amount to about six metres on the ground. The Inkpen test point is in fact an old triangulation pillar and the point as transformed by Ubuntu sits exactly on this when viewed in Goorgle Earth. Any ideas? Nick. -- View this message in context: http://osgeo-org.1560.n6.nabble.com/OSGB-coordinates-to-WGS84-lat-lon-problem-tp4965339.html Sent from the Quantum GIS - User mailing list archive at Nabble.com. _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user -- The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England & Wales and a charity registered in Scotland (SC 038302). _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
