SineStarFactory.java example

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com.revolsys.open-master
/*
 * 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.revolsys.geometry.model.util;

import com.revolsys.geometry.model.BoundingBox;
import com.revolsys.geometry.model.Geometry;
import com.revolsys.geometry.model.GeometryFactory;
import com.revolsys.geometry.model.LinearRing;
import com.revolsys.geometry.model.Polygon;
import com.revolsys.geometry.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 {
  protected double armLengthRatio = 0.5;

  protected int numArms = 8;

  /**
   * Creates a factory which will create sine stars using the default
   * {@link GeometryFactory}.
   *
   * @param geomFact the factory to use
   */
  public SineStarFactory() {
    super();
  }

  /**
   * Creates a factory which will create sine stars using the given
   * {@link GeometryFactory}.
   *
   * @param geomFact the factory to use
   */
  public SineStarFactory(final GeometryFactory geomFact) {
    super(geomFact);
  }

  /**
   * Generates the geometry for the sine star
   *
   * @return the geometry representing the sine star
   */
  public Geometry newSineStar() {
    final BoundingBox env = this.dim.getEnvelope();
    final double radius = env.getWidth() / 2.0;

    double armRatio = this.armLengthRatio;
    if (armRatio < 0.0) {
      armRatio = 0.0;
    }
    if (armRatio > 1.0) {
      armRatio = 1.0;
    }

    final double armMaxLen = armRatio * radius;
    final double insideRadius = (1 - armRatio) * radius;

    final double centreX = env.getMinX() + radius;
    final double centreY = env.getMinY() + radius;

    final double[] coordinates = new double[(this.vertexCount + 1) * 2];
    int coordinateIndex = 0;
    for (int i = 0; i < this.vertexCount; i++) {
      // the fraction of the way thru the current arm - in [0,1]
      final double ptArcFrac = i / (double)this.vertexCount * this.numArms;
      final double armAngFrac = ptArcFrac - Math.floor(ptArcFrac);

      // the angle for the current arm - in [0,2Pi]
      // (each arm is a complete sine wave cycle)
      final double armAng = 2 * Math.PI * armAngFrac;
      // the current length of the arm
      final double armLenFrac = (Math.cos(armAng) + 1.0) / 2.0;

      // the current radius of the curve (core + arm)
      final double curveRadius = insideRadius + armMaxLen * armLenFrac;

      // the current angle of the curve
      final double ang = i * (2 * Math.PI / this.vertexCount);
      final double x = curveRadius * Math.cos(ang) + centreX;
      final double y = curveRadius * Math.sin(ang) + centreY;
      coordinates[coordinateIndex++] = this.geomFact.makeXyPrecise(x);
      coordinates[coordinateIndex++] = this.geomFact.makeXyPrecise(y);
    }

    final LinearRing ring = this.geomFact.linearRing(2, coordinates);
    final Polygon poly = this.geomFact.polygon(ring);
    return poly;
  }

  /**
   * Sets the ration of the length of each arm to the distance from the tip
   * of the arm to the centre of the star.
   * Value should be between 0.0 and 1.0
   *
   * @param armLengthRatio
   */
  public void setArmLengthRatio(final double armLengthRatio) {
    this.armLengthRatio = armLengthRatio;
  }

  /**
   * Sets the number of arms in the star
   *
   * @param numArms the number of arms to generate
   */
  public void setNumArms(final int numArms) {
    this.numArms = numArms;
  }
}