OpenStreetMap
Found myself at the Royal Observatory this morning (on the map), and discovered a bit of trivia since I expected to be located at longitude: 0°0 as my geography class would have made me believe. Well, its not:
Prime meridian at Greenwich. CC-by-sa ChrisO
The prime meridian established at the Royal Observatory, Greenwich in 1851 is actually at 0°0′5.3″W, thats 102m west of the the 0°0 prime meridian used in the WGS 84 coordinate system. Why? Because the modern coordinate system was corrected to have its origin at the Earth’s centre of mass.
Read more at https://en.wikipedia.org/wiki/Prime_meridian#International_prime_meridian
GPS coordinate at the Greenwich meridian. CC-by-sa Jckcip
Discussion
Comment from andy mackey on 31 August 2016 at 16:08
I had been told that it had been adjusted, Thanks for linking me to more information.
Comment from BushmanK on 31 August 2016 at 16:38
Question is, what exactly you call “the Greenwich meridian” - several things sharing this name. EPSG:8901 is a zero longitude line and it is called “Greenwich meridian”. But historical Greenwich meridian mark is not a zero anymore, as explained above.
Comment from Boston Logan Taxi on 31 August 2016 at 18:29
kool, that is some news. Even till date I thought it was 0,0 on the lat-long map. Thanks for bring this up and clarifying it for us so well.
Comment from Warin61 on 31 August 2016 at 22:34
The first ‘refinement’ of wgs84 moved it by ~1.5 metres, subsequent ‘refinements’ are in the order of 0.1 metres. I don’t know if these are all in the one general direction (and therefore cumulative) or in random directions. There is, I believe, at least one datum with 0 running through Meca.
I’d think the historical Greenwich meridian mark was used as 0, and probably that is still the case for some maps … probably very old ones.
Comment from TheSwavu on 1 September 2016 at 23:17
The real story is that there are two groups of people who are interested in where the Prime Meridian is:
Turns out the time people were the ones that spent all the effort and money worrying about measuring the rotation of the planet and they wanted their time scales to be constant. By the time the space people found out it was too late (apparently it would have been perfectly feasible to have nudged the time people to line up with the space people but the chance was missed).
There is a journal paper on the subject