SineStarFactory.java
/*
* Copyright (c) 2016 Vivid Solutions.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
* and the Eclipse Distribution License is available at
*
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.locationtech.jts.geom.util;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Envelope;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.LinearRing;
import org.locationtech.jts.geom.Polygon;
import org.locationtech.jts.util.GeometricShapeFactory;
/**
* Creates geometries which are shaped like multi-armed stars
* with each arm shaped like a sine wave.
* These kinds of geometries are useful as a more complex
* geometry for testing algorithms.
*
* @author Martin Davis
*
*/
public class SineStarFactory
extends GeometricShapeFactory
{
/**
* Creates a sine star with the given parameters.
*
* @param origin the origin point
* @param size the size of the star
* @param nPts the number of points in the star
* @param nArms the number of arms to generate
* @param armLengthRatio the arm length ratio
* @return a sine star shape
*/
public static Geometry create(Coordinate origin, double size, int nPts, int nArms, double armLengthRatio) {
SineStarFactory gsf = new SineStarFactory();
gsf.setCentre(origin);
gsf.setSize(size);
gsf.setNumPoints(nPts);
gsf.setArmLengthRatio(armLengthRatio);
gsf.setNumArms(nArms);
Geometry poly = gsf.createSineStar();
return poly;
}
protected int numArms = 8;
protected double armLengthRatio = 0.5;
/**
* Creates a factory which will create sine stars using the default
* {@link GeometryFactory}.
*/
public SineStarFactory()
{
super();
}
/**
* Creates a factory which will create sine stars using the given
* {@link GeometryFactory}.
*
* @param geomFact the factory to use
*/
public SineStarFactory(GeometryFactory geomFact)
{
super(geomFact);
}
/**
* Sets the number of arms in the star
*
* @param numArms the number of arms to generate
*/
public void setNumArms(int numArms)
{
this.numArms = numArms;
}
/**
* Sets the ratio of the length of each arm to the radius of the star.
* A smaller number makes the arms shorter.
* Value should be between 0.0 and 1.0
*
* @param armLengthRatio the ratio determining the length of them arms.
*/
public void setArmLengthRatio(double armLengthRatio)
{
this.armLengthRatio = armLengthRatio;
}
/**
* Generates the geometry for the sine star
*
* @return the geometry representing the sine star
*/
public Geometry createSineStar()
{
Envelope env = dim.getEnvelope();
double radius = env.getWidth() / 2.0;
double armRatio = armLengthRatio;
if (armRatio < 0.0)
armRatio = 0.0;
if (armRatio > 1.0)
armRatio = 1.0;
double armMaxLen = armRatio * radius;
double insideRadius = (1 - armRatio) * radius;
double centreX = env.getMinX() + radius;
double centreY = env.getMinY() + radius;
Coordinate[] pts = new Coordinate[nPts + 1];
int iPt = 0;
for (int i = 0; i < nPts; i++) {
// the fraction of the way through the current arm - in [0,1]
double ptArcFrac = (i / (double) nPts) * numArms;
double armAngFrac = ptArcFrac - Math.floor(ptArcFrac);
// the angle for the current arm - in [0,2Pi]
// (each arm is a complete sine wave cycle)
double armAng = 2 * Math.PI * armAngFrac;
// the current length of the arm
double armLenFrac = (Math.cos(armAng) + 1.0) / 2.0;
// the current radius of the curve (core + arm)
double curveRadius = insideRadius + armMaxLen * armLenFrac;
// the current angle of the curve
double ang = i * (2 * Math.PI / nPts);
double x = curveRadius * Math.cos(ang) + centreX;
double y = curveRadius * Math.sin(ang) + centreY;
pts[iPt++] = coord(x, y);
}
pts[iPt] = new Coordinate(pts[0]);
LinearRing ring = geomFact.createLinearRing(pts);
Polygon poly = geomFact.createPolygon(ring);
return poly;
}
}