/* GeoGebra - Dynamic Mathematics for Everyone http://www.geogebra.org This file is part of GeoGebra. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation. */ /* * AlgoCircleThreePoints.java * * Created on 15. November 2001, 21:37 */ package geogebra.kernel; import geogebra.euclidian.EuclidianConstants; import geogebra.kernel.kernelND.GeoConicND; import geogebra.kernel.kernelND.GeoPointND; /** * * @author Markus * @version */ public class AlgoCircleThreePoints extends AlgoElement { /** * */ private static final long serialVersionUID = 1L; private GeoPointND A, B, C; // input protected GeoConicND circle; // output // line bisectors private GeoLine s0, s1; private GeoPoint center; private double[] det = new double[3]; transient private double ax, ay, bx, by, cx, cy, ABx, ABy, ACx, ACy, BCx, BCy, maxDet; transient private int casenr; protected AlgoCircleThreePoints( Construction cons, String label, GeoPointND A, GeoPointND B, GeoPointND C) { this(cons, A, B, C); circle.setLabel(label); } public AlgoCircleThreePoints( Construction cons, GeoPointND A, GeoPointND B, GeoPointND C) { super(cons); setPoints(A,B,C); createCircle(); circle.addPointOnConic(getA()); //move into setIncidence(); circle.addPointOnConic(getB()); circle.addPointOnConic(getC()); // temp: line bisectors s0 = new GeoLine(cons); s1 = new GeoLine(cons); center = new GeoPoint(cons); setInputOutput(); // for AlgoElement compute(); setIncidence(); } private void setIncidence() { if (A instanceof GeoPoint) ((GeoPoint) A).addIncidence(circle); if (B instanceof GeoPoint) ((GeoPoint) B).addIncidence(circle); if (C instanceof GeoPoint) ((GeoPoint) C).addIncidence(circle); } /** set the three points of the circle to A, B, C * @param A first point * @param B second point * @param C third point */ protected void setPoints(GeoPointND A, GeoPointND B, GeoPointND C){ this.A = A; this.B = B; this.C = C; } /** * create the object circle */ protected void createCircle(){ circle = new GeoConic(cons); } public String getClassName() { return "AlgoCircleThreePoints"; } public int getRelatedModeID() { return EuclidianConstants.MODE_CIRCLE_THREE_POINTS; } // for AlgoElement protected void setInputOutput() { setInput(); setOutput(); setDependencies(); // done by AlgoElement } protected void setInput() { input = new GeoElement[3]; input[0] = (GeoElement) A; input[1] = (GeoElement) B; input[2] = (GeoElement) C; } protected void setOutput() { output = new GeoElement[1]; output[0] = circle; } public GeoConicND getCircle() { return circle; } public GeoPoint getA() { return (GeoPoint) A; } public GeoPoint getB() { return (GeoPoint) B; } public GeoPoint getC() { return (GeoPoint) C; } // compute circle through A, B, C protected void compute() { // A, B or C undefined if (!getA().isFinite() || !getB().isFinite() || !getC().isFinite()) { circle.setUndefined(); return; } // get inhomogenous coords of points ax = ((GeoPoint) getA()).inhomX; ay = ((GeoPoint) getA()).inhomY; bx = ((GeoPoint) getB()).inhomX; by = ((GeoPoint) getB()).inhomY; cx = ((GeoPoint) getC()).inhomX; cy = ((GeoPoint) getC()).inhomY; // A = B = C if (kernel.isEqual(ax, bx) && kernel.isEqual(ax, cx) && kernel.isEqual(ay, by) && kernel.isEqual(ay, cy)) { circle.setCircle((GeoPoint) getA(), 0.0); // single point return; } // calc vectors AB, AC, BC ABx = bx - ax; ABy = by - ay; ACx = cx - ax; ACy = cy - ay; BCx = cx - bx; BCy = cy - by; double lengthAB = GeoVec2D.length(ABx, ABy); double lengthAC = GeoVec2D.length(ACx, ACy); double lengthBC = GeoVec2D.length(BCx, BCy); // find the two bisectors with max intersection angle // i.e. maximum abs of determinant of directions // max( abs(det(AB, AC)), abs(det(AC, BC)), abs(det(AB, BC)) ) det[0] = Math.abs(ABx * ACy - ABy * ACx) / (lengthAB * lengthAC); // AB, AC det[1] = Math.abs(ACx * BCy - ACy * BCx) / (lengthAC * lengthBC); // AC, BC det[2] = Math.abs(ABx * BCy - ABy * BCx) / (lengthAB * lengthBC); // AB, BC // take ip[0] as init minimum and find minimum case maxDet = det[0]; casenr = 0; if (det[1] > maxDet) { casenr = 1; maxDet = det[1]; } if (det[2] > maxDet) { casenr = 2; maxDet = det[2]; } // A, B, C are collinear: set M to infinite point // in perpendicular direction of AB if (kernel.isZero(maxDet)) { center.setCoords(-ABy, ABx, 0.0d); circle.setCircle(center, (GeoPoint) getA()); } // standard case else { // intersect two line bisectors according to casenr switch (casenr) { case 0 : // bisectors of AB, AC s0.x = ABx; s0.y = ABy; s0.z = - ((ax + bx) * s0.x + (ay + by) * s0.y) / 2.0; s1.x = ACx; s1.y = ACy; s1.z = - ((ax + cx) * s1.x + (ay + cy) * s1.y) / 2.0; break; case 1 : // bisectors of AC, BC s1.x = ACx; s1.y = ACy; s1.z = - ((ax + cx) * s1.x + (ay + cy) * s1.y) / 2.0; s0.x = BCx; s0.y = BCy; s0.z = - ((bx + cx) * s0.x + (by + cy) * s0.y) / 2.0; break; case 2 : // bisectors of AB, BC s0.x = ABx; s0.y = ABy; s0.z = - ((ax + bx) * s0.x + (ay + by) * s0.y) / 2.0; s1.x = BCx; s1.y = BCy; s1.z = - ((bx + cx) * s1.x + (by + cy) * s1.y) / 2.0; break; } // intersect line bisectors to get midpoint GeoVec3D.cross(s0, s1, center); circle.setCircle(center, center.distance(getA())); } } public String toString() { // Michael Borcherds 2008-03-30 // simplified to allow better Chinese translation return app.getPlain("CircleThroughABC",A.getLabel(),B.getLabel(),C.getLabel()); } }