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
Error occurred while calculating annotation data.
Log Message:	Added missing RCSid tag
#	Content
1	{ RCSid $Id$ }
2	{
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));