cal/cal/circle.cal

{ RCSid $Id$ }
{
        Calculate center and radius of circle based on three
        points in the plane.

        Beware colinear points and points parallel to y-axis.

        6/4/2002        Greg Ward
                        solution due to Paul Bourke

        Inputs:

        x1,y1,x2,y2,x3,y3       - points on circle

        Outputs:

        xc, yc, r               - center and radius
}
sq(x) : x*x;

ma = (y2-y1)/(x2-x1);
mb = (y3-y2)/(x3-x2);

xc = (ma*mb*(y1-y3) + mb*(x1+x2) - ma*(x2+x3)) / (2*(mb-ma));

yc = ((x1+x2)/2 - xc)/ma + (y1+y2)/2;

r = sqrt(sq(x2-xc) + sq(y2-yc));
Revision:	1.2
Committed:	Wed Nov 21 18:10:45 2018 UTC (5 years, 5 months ago) by greg
Branch:	MAIN
CVS Tags:	rad5R4, rad5R3, HEAD
Changes since 1.1:	+1 -0 lines
Log Message:	Added missing RCSid tag
#	User	Rev	Content
1	greg	1.2	{ RCSid $Id$ }
2	greg	1.1	{
3			Calculate center and radius of circle based on three
4			points in the plane.
5
6			Beware colinear points and points parallel to y-axis.
7
8			6/4/2002 Greg Ward
9			solution due to Paul Bourke
10
11			Inputs:
12
13			x1,y1,x2,y2,x3,y3 - points on circle
14
15			Outputs:
16
17			xc, yc, r - center and radius
18			}
19			sq(x) : x*x;
20
21			ma = (y2-y1)/(x2-x1);
22			mb = (y3-y2)/(x3-x2);
23
24			xc = (mamb(y1-y3) + mb(x1+x2) - ma(x2+x3)) / (2*(mb-ma));
25
26			yc = ((x1+x2)/2 - xc)/ma + (y1+y2)/2;
27
28			r = sqrt(sq(x2-xc) + sq(y2-yc));