Er, any comments...or should I be posting this some place else? P=| On Dec 4, 4:41 pm, Kaimbridge <[email protected]> wrote: > The current default radius used in Google Maps distance calculations > is the WGS-84 equatorial radius, "a", 6378.137 km (6378137 m). > While "a" is ideal along the equator, that is only one extreme: The > other is along a north-south meridian, which approximately equals "[.5* > (a^2+b^2)]^.5", the "elliptical quadratic mean". For WGS-84, this > works out to 6367.454, with the actual meridional value being about > 6367.449 km. > If you average the two extremes, you get the "ellipsoidal quadratic > mean", "Qr": > > / equatorial^2 + meridional^2 \^.5 > Qr = (-------------------------------), > \ 2 / > > / a^2 + .5*(a^2+b^2) \^.5 > = (----------------------), > \ 2 / > > / 3*a^2 + b^2 \^.5 > = (---------------); > \ 4 / > > So, for the WGS-84 spheroid model, where a = 6378.137 and > b = 6356.752314, Qr ~=~ 6372.7975559, 6372.797 or——given all of the > different "flavors" discussed in the "Talk:Earth" link given in the > link below—— even just rounded to "6372.8"! See: > > http://groups.google.com/group/comp.infosystems.gis/msg/5897cf05c924a569 > > for a fuller explanation why, as well as the Wikipedia link to an even > much more thorough explanation. > > ~Kaimbridge~ > > ----- > Wikipedia—Contributor Home Page: > > http://en.wikipedia.org/wiki/User:Kaimbridge > > ***** Void Where Permitted; Limit 0 Per Customer. *****
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