Re: formula for great circle computation

From: (Mark Brader)
Organization: SoftQuad Inc., Toronto, Canada
Date:         13 Oct 95 01:30:28 
References:   1 2
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Karl Swartz (kls@ohare.Chicago.COM) writes:

>     acos( sin(lat1) * sin(lat2)  + cos(lat1) * cos(lat2) * cos(theta) )

[Where acos is done in radians]

> Multiply that by the radius of the earth (i.e., 6371.2 kilometers) to
> get a reasonable approximation of the great circle distance.

Right, it's a reasonable approximation.  So don't be fooled by that
"6371.2 km" -- that implies a spurious degree of precision.  The radius
of the Earth varies by more then 40 km between poles and equator.
And if you want the distance flown rather than the ground distance
covered, you also need to take the flying altitude into account!

Mark Brader,       "I'm not a lawyer, but I'm pedantic and
SoftQuad Inc., Toronto         that's just as good."      -- D Gary Grady

My text in this article is in the public domain.