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[help-3dldf] Re: [metapost] Constructing ellipse from 4 points
From: |
Laurence Finston |
Subject: |
[help-3dldf] Re: [metapost] Constructing ellipse from 4 points |
Date: |
Wed, 2 Nov 2005 20:10:12 +0100 (MET) |
On Wed, 2 Nov 2005, Brooks Moses wrote:
> A Google search on "ellipse construct 'four points'" finds the following
> links:
>
> http://steiner.math.nthu.edu.tw/ne01/whw/Ellipse1/part2.htm
> http://mathworld.wolfram.com/ConicSection.html
> http://mathworld.wolfram.com/Ellipse.html
Aha! I just searched for "ellipse constructions" and found a lot of sites
that didn't look too promising. Thanks.
>
> The short form is that, to construct an ellipse, you need either five
> points, four points and a tangent line, or four points and knowledge of the
> direction of the major and minor axes.
I can get more points by finding the intersections of the plane with more
of the ellipses on the ellipsoid, and I can get as many of those as I
want.
> Beyond that, I don't know. My guess is that finding the direction of the
> major and minor axes and using that construction is the way to go.
Thank you for your quick answer.
Laurence
- [help-3dldf] Re: [metapost] Constructing ellipse from 4 points,
Laurence Finston <=