Xref: utzoo comp.graphics:3389 sci.math:4661
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!n8emr!uncle!oink!jep
From: jep@oink.UUCP (James E. Prior)
Newsgroups: comp.graphics,sci.math
Subject: Re: simple spherical algebra question
Message-ID: <304@oink.UUCP>
Date: 17 Oct 88 23:43:51 GMT
References: <1187@agora.UUCP> <785@uwovax.uwo.ca>
Reply-To: jep@oink.UUCP (James E. Prior)
Organization: Random Prime Research Institute  Columbus, Ohio
Lines: 24

In article <1187@agora.UUCP>, rickc@agora.UUCP (Rick Coates) writes:
> Here is a straightforward question that I have not been able to find
> in my reference books:
> 
> 	Given two points on a sphere, what is the equation of the
> 	line (great circle) between them?  What is the midpoint?
> 
> Many thanks in advance,
> 
> Rick Coates

There are jillions of spheres that pass through any two given points.
Presuming that you know of a particular sphere, i.e. its center,

The great circle is the intersection of the sphere, and the plane
defined by the sphere's center and the two given points.

You may find it handy to derive the formula for the plane by remembering
that the cross product of the two non-parallel vectors lieing in a plane,
is perpendicular to that plane.
-- 
Jim Prior    osu-cis!n8emr!oink!jep    jep@oink.UUCP

Pointers are my friend.