On 19/03/2009 22:33, Andy Robinson wrote: > Ian Wills wrote: > >> I have noticed a puzzling thing that applies to OSM, Yahoo and Google maps. >> >> The origin of longitude (zero longitude) should run through the Royal >> Observatory at Greenwich, near London. Specifically it should run >> through the optical axis of the transit telescope in the Transit >> Building at Greenwich. Certainly, the Greenwich observatory people >> think so. Not only is the zero meridian marked on the ground but the >> gift shop sells zero meridian T shirts, mugs and all the usual kitsch. >> >> The Observatory's website thinks so too - see >> http://www.nmm.ac.uk/places/royal-observatory/meridian-line/ >> >> My problem is that in OSM, the zero meridian does not run through the >> Transit Building where it should. Here is a permalink: >> >> http://www.openstreetmap.org/?lat=51.47786&lon=-0.001528&zoom=18 >> >> That is, at a longitude of -0.001528. >> >> The Transit building is quite clear in the Yahoo image but OSM puts >> the zero meridian about 100 metres to the east of the meridian line. >> >> OSM and Yahoo are not alone in this, Google maps does the same. Try >> entering +51° 28' 40.27", +0° 0' 0.01" into Google maps and check the >> image. (You will need the fraction of a second). >> >> The resolution of longitude at the latitude of Greenwich is about 1 >> metre so OSM, Yahoo and Google should be able to get closer than 100 >> metres. >> >> - I find it hard to believe that all mapping, or at least mapping in >> the UK, is out by 100m. Can anyone explain this discrepancy? >> >> - Has anyone been to the meridian line at Greenwich with a GPS to >> check the position? >> >>
> http://en.wikipedia.org/wiki/WGS84 should answer your question > > Cheers > > Andy > > _______________________________________________ > newbies mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/newbies > _______________________________________________ newbies mailing list [email protected] http://lists.openstreetmap.org/listinfo/newbies
