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package org.reprap.geometry.polygons;
import org.reprap.Preferences;
/**
* Small class to hold circles (centre and squared radius)
*
*/
public class RrCircle {
private Rr2Point centre;
private double radius2;
/**
* Constructor makes a circle from three points on its
* circumference.
* (See "A Programmer's Geometry" p 65, by Adrian Bowyer and John Woodwark)
* @param pk
* @param pl
* @param pm
*/
public RrCircle(Rr2Point k, Rr2Point l, Rr2Point m) throws RrParallelLineException
{
Rr2Point lk = Rr2Point.sub(l, k);
Rr2Point mk = Rr2Point.sub(m, k);
double det = Rr2Point.op(lk, mk);
if(Math.abs(det) < Preferences.tiny())
throw new RrParallelLineException("RrCircle: colinear points.");
double lk2 = Rr2Point.mul(lk, lk);
double mk2 = Rr2Point.mul(mk, mk);
Rr2Point lkt = new Rr2Point(lk2, lk.y());
Rr2Point mkt = new Rr2Point(mk2, mk.y());
double x = 0.5*Rr2Point.op(lkt, mkt)/det;
lkt = new Rr2Point(lk.x(), lk2);
mkt = new Rr2Point(mk.x(), mk2);
double y = 0.5*Rr2Point.op(lkt, mkt)/det;
radius2 = x*x + y*y;
centre = new Rr2Point(x + k.x(), y + k.y());
}
public Rr2Point centre()
{
return centre;
}
public double radiusSquared()
{
return radius2;
}
}
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