Josh English wrote in message <371BC172.F6F8B0AC@spiritone.com>...
>Thank you for the circumference formula... I've been looking for it.
>

It's an approximation, of course. The exact circumference is caclulated with
integrals.

As for your other method, I don't know... I think you'd need the foci of the
ellipse to calculate the radius. The sum of the distances from a point on
the ellipse to the foci is constant:
X - an arbitrary point on the ellipse
F1 and F2 - foci

XF1 + XF2 = 2 * major radius

You can also deduct that the distance from a focal point to the point where
the ellipse's radius is smallest (minor radius) = the major radius

It should now be quite easy to find the foci, given the major and minor
axes. From there, a bit of trig should give you the radius for any angle.
I'm thinking this up as I go, so I might be quite wrong. But if you feel
like it, give it a try (I don't feel like it, sorry :)

Margus

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