Update the mean earth radius number

[sakisdog]

Based on http://en.wikipedia.org/wiki/Earth_radius and some Google Maps distance calculations i think this change produces more accurate results.

[mikalhart]

I see @ress997 comment that the suggest new value is accepted by the Japan Meteorological Agency. Are there any other thoughts out there? Has anyone encountered problems with the old value? I'd love just a bit more evidence that a change is for the better and won't hurt anyone.

[sakisdog]

I don't think that there is a problem between small distances with the old value. But in calculation between long distances there is a big difference. I created a small example between 2 places (London and Edinburgh). Using Google Maps measure tool i found that the result of 6371009 value is the same as Google's.
Also based on this International Union of Geodesy and Geophysics (IUGG) and International Earth Rotation and Reference Systems Service (IERS) use 6371008.7714 (6371009 with rounding) as mean eath radius.