{
	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));