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On 30/04/2014 17:37, Douglas Bateman
wrote:
This is a new club consisting, so far, of two members: Frank King and myself.After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) I would be all in favour of marking the zero meridian for the whole of its length on land, if that's the intention. Why is the difference 90 metres ? Wikipedia says 200 metres ("102.5 metres east of its last position") at http://en.wikipedia.org/wiki/Meridian_%28geography%29 - see also http://en.wikipedia.org/wiki/Prime_meridian http://wikimapia.org/3323604/Meridian-Building says :- "Curiously, whether by accident or design, the location of the WGS84 0° meridian is marked in Greenwich by the presence of a waste basket on the path leading more or less due east from the observatory containing the transit telescope." Is it the old thing about GPS receivers being deliberately inaccurate to preserve military secrets, or is it that dedicated GPS receivers are more accurate than smart phones and tablets ? I know that Harriet James used a hand held GPS receiver when measuring the location of my house. -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK |
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