SierpinskiCarpetBuilder.java

/*
* The JTS Topology Suite is a collection of Java classes that
* implement the fundamental operations required to validate a given
* geo-spatial data set to a known topological specification.
*
* Copyright (C) 2001 Vivid Solutions
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*
* For more information, contact:
*
*     Vivid Solutions
*     Suite #1A
*     2328 Government Street
*     Victoria BC  V8T 5G5
*     Canada
*
*     (250)385-6040
*     www.vividsolutions.com
*/

package com.vividsolutions.jts.shape.fractal;

import java.util.*;

import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jts.shape.*;

public class SierpinskiCarpetBuilder 
extends GeometricShapeBuilder
{
	private CoordinateList coordList = new CoordinateList();
	
	public SierpinskiCarpetBuilder(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 origin = baseLine.getCoordinate(0);
		LinearRing[] holes = getHoles(level, origin.x, origin.y, getDiameter());
		LinearRing shell = (LinearRing) ((Polygon) geomFactory.toGeometry(getSquareExtent())).getExteriorRing();
		return geomFactory.createPolygon(
				shell, holes);
	}
	
	private LinearRing[] getHoles(int n, double originX, double originY, double width) 
	{
		List holeList = new ArrayList();
		
		addHoles(n, originX, originY, width, holeList );
		
		return GeometryFactory.toLinearRingArray(holeList);
	}

	private void addHoles(int n, double originX, double originY, double width, List holeList) 
	{
		if (n < 0) return;
		int n2 = n - 1;
		double widthThird = width / 3.0;
		double widthTwoThirds = width * 2.0 / 3.0;
		double widthNinth = width / 9.0;
		addHoles(n2, originX, 									originY, widthThird, holeList);
		addHoles(n2, originX + widthThird, 			originY, widthThird, holeList);
		addHoles(n2, originX + 2 * widthThird, 	originY, widthThird, holeList);
		
		addHoles(n2, originX, 									originY + widthThird, widthThird, holeList);
		addHoles(n2, originX + 2 * widthThird, 	originY + widthThird, widthThird, holeList);

		addHoles(n2, originX, 									originY + 2 * widthThird, widthThird, holeList);
		addHoles(n2, originX + widthThird, 			originY + 2 * widthThird, widthThird, holeList);
		addHoles(n2, originX + 2 * widthThird, 	originY + 2 * widthThird, widthThird, holeList);

		// add the centre hole
		holeList.add(createSquareHole(originX + widthThird, originY + widthThird, widthThird));
	}

	private LinearRing createSquareHole(double x, double y, double width)
	{
		Coordinate[] pts = new Coordinate[]{
        new Coordinate(x, y),
        new Coordinate(x + width, y),
        new Coordinate(x + width, y + width),
        new Coordinate(x, y + width),
        new Coordinate(x, y)
        }	;
		return geomFactory.createLinearRing(pts); 
	}
	

}