From: ovek AT arcticnet DOT no (Ove Kaaven)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: ellipses at an angle
Date: Tue, 04 Feb 1997 09:33:04 GMT
Organization: Vplan Programvare AS
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Message-ID: <5d82fe$6v7$1@troll.powertech.no>
References: <199702030225 DOT UAA22378 AT mail DOT texoma DOT net>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

"Mark S. Teel" <mteel AT texoma DOT net> wrote:

>>that: picture an ellipse leaning against a wall, what algorithm would 
>>I
>>use to draw that?
>>
>>Shawn Betts
>>
>:Well, you could use the original definition of an ellipse (that is, from
>:any point on the ellipse, the sum of the distances from that point to the
>:two foci equals 1).  The math gets a little messy though.

>No!  This is not even the definition of an ellipse parallel to a coordinate
>axis!

An ellipse can be expressed as all points whose the sum of the two
distances from the point to the two foci is equal. (I don't know where
he got 1 from, but this sum will remain constant.) Check with any book
on geometry.

You can plot an ellipse by sticking two nails in paper (the two foci),
connecting them with an arbitrary length of thread, then plotting by
holding a pencil tight against the thread (which will maintain a
constant sum of distances to foci).

This is one possible definition of an ellipse, and it's independent of
mathematics.