TQ2549 : Trig point S3328 Reigate Park

taken 7 years ago, near to Reigate, Surrey, Great Britain

Trig point S3328 Reigate Park
Trig point S3328 Reigate Park
A significant photograph for the photographer, as it led him to understand why his GPS seemed to show a fairly consistent error about 7 m too far north in this part of the world. Officially, this point is at TQ 2514849422. With an excellent view of the sky and plenty of differential satellites, the GPS showed a location of TQ 2515149429 when about 3 m due east of the trig point, instead of TQ2515149422. Buried in the Geograph discussion group was a thread giving the explanation. Etrex devices use the Molodensky transformation between British grid coordinates and WGS84 latitude and longitude. This is inaccurate by varying amounts over the country when compared with the official OSTN02 transformation, and is about 7 m too far north for TQ. It is spot-on for eastings in TQ. With this correction, the GPS was extremely accurate.
Creative Commons Licence [Some Rights Reserved]   © Copyright Robin Webster and licensed for reuse under this Creative Commons Licence.
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TQ2549, 373 images   (more nearby )
Photographer
  (find more nearby)
Date Taken
Thursday, 1 July, 2010   (more nearby)
Submitted
Thursday, 1 July, 2010
Category
Trig Point   (more nearby)
Subject Location
OSGB36: geotagged! TQ 25148 49422 [1m precision]
WGS84: 51:13.8164N 0:12.5387W
Camera Location
OSGB36: geotagged! TQ 25151 49422
View Direction
WEST (about 270 degrees)
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