Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!hsdndev!cmcl2!kramden.acf.nyu.edu!brnstnd
From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.c
Subject: Re: Efficient algorithm needed
Message-ID: <11959:Mar2000:15:3791@kramden.acf.nyu.edu>
Date: 20 Mar 91 00:15:37 GMT
References: <2538@odin.cs.hw.ac.uk> <4987@goanna.cs.rmit.oz.au> <27497@uflorida.cis.ufl.EDU>
Organization: IR
Lines: 20
X-Right-Newsgroups: comp.programming

In article <27497@uflorida.cis.ufl.EDU> jdb@reef.cis.ufl.edu (Brian K. W. Hook) writes:
> Given an ellipse and a point, determine where a line from the center of the
> ellipse to the point will intersect the ellipse.
> You are give:
> The center of the ellipse
> The width of ellipse
> The height of the ellipse
> The X and Y coordinate of the point

What is the ellipse's orientation?

If it is not rotated, then a point (x,y) is on the edge of the ellipse
only if ((x - c)/w)^2 + ((y - d)/h)^2 = 1, where (c,d) is the center and
(h,w) are half of height and width. So to scale a point (x,y) to the
edge you should subtract (c,d), then divide by sqrt((x/w)^2 + (y/h)^2),
then add (c,d) back in.

Now what does this have to do with the C language?

---Dan