package com.vividsolutions.jts.shape.fractal;
import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jts.math.Vector2D;
import com.vividsolutions.jts.shape.*;
public class KochSnowflakeBuilder
extends GeometricShapeBuilder
{
private CoordinateList coordList = new CoordinateList();
public KochSnowflakeBuilder(GeometryFactory geomFactory)
{
super(geomFactory);
}
public static int recursionLevelForSize(int numPts)
{
double pow4 = numPts / 3;
double exp = Math.log(pow4)/Math.log(4);
return (int) exp;
}
public Geometry getGeometry()
{
int level = recursionLevelForSize(numPts);
LineSegment baseLine = getSquareBaseLine();
Coordinate[] pts = getBoundary(level, baseLine.getCoordinate(0), baseLine.getLength());
return geomFactory.createPolygon(
geomFactory.createLinearRing(pts), null);
}
/**
* The height of an equilateral triangle of side one
*/
private static double HEIGHT_FACTOR = Math.sin(Math.PI / 3.0);
private static final double ONE_THIRD = 1.0/3.0;
private static final double THIRD_HEIGHT = HEIGHT_FACTOR/3.0;
private static final double TWO_THIRDS = 2.0/3.0;
private Coordinate[] getBoundary(int level, Coordinate origin, double width)
{
double y = origin.y;
// for all levels beyond 0 need to vertically shift shape by height of one "arm" to centre it
if (level > 0) {
y += THIRD_HEIGHT * width;
}
Coordinate p0 = new Coordinate(origin.x, y);
Coordinate p1 = new Coordinate(origin.x + width/2, y + width * HEIGHT_FACTOR);
Coordinate p2 = new Coordinate(origin.x + width, y);
addSide(level, p0, p1);
addSide(level, p1, p2);
addSide(level, p2, p0);
coordList.closeRing();
return coordList.toCoordinateArray();
}
public void addSide(int level, Coordinate p0, Coordinate p1) {
if (level == 0)
addSegment(p0, p1);
else {
Vector2D base = Vector2D.create(p0, p1);
Coordinate midPt = base.multiply(0.5).translate(p0);
Vector2D heightVec = base.multiply(THIRD_HEIGHT);
Vector2D offsetVec = heightVec.rotateByQuarterCircle(1);
Coordinate offsetPt = offsetVec.translate(midPt);
int n2 = level - 1;
Coordinate thirdPt = base.multiply(ONE_THIRD).translate(p0);
Coordinate twoThirdPt = base.multiply(TWO_THIRDS).translate(p0);
// construct sides recursively
addSide(n2, p0, thirdPt);
addSide(n2, thirdPt, offsetPt);
addSide(n2, offsetPt, twoThirdPt);
addSide(n2, twoThirdPt, p1);
}
}
private void addSegment(Coordinate p0, Coordinate p1)
{
coordList.add(p1);
}
}