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Java example source code file (AbstractConvexHullGenerator2D.java)

This example Java source code file (AbstractConvexHullGenerator2D.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

abstractconvexhullgenerator2d, collection, convergenceexception, convexhull2d, default_tolerance, mathillegalargumentexception, nullargumentexception, util

The AbstractConvexHullGenerator2D.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math3.geometry.euclidean.twod.hull;

import java.util.Collection;

import org.apache.commons.math3.exception.ConvergenceException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.geometry.euclidean.twod.Vector2D;
import org.apache.commons.math3.util.MathUtils;

/**
 * Abstract base class for convex hull generators in the two-dimensional euclidean space.
 *
 * @since 3.3
 */
abstract class AbstractConvexHullGenerator2D implements ConvexHullGenerator2D {

    /** Default value for tolerance. */
    private static final double DEFAULT_TOLERANCE = 1e-10;

    /** Tolerance below which points are considered identical. */
    private final double tolerance;

    /**
     * Indicates if collinear points on the hull shall be present in the output.
     * If {@code false}, only the extreme points are added to the hull.
     */
    private final boolean includeCollinearPoints;

    /**
     * Simple constructor.
     * <p>
     * The default tolerance (1e-10) will be used to determine identical points.
     *
     * @param includeCollinearPoints indicates if collinear points on the hull shall be
     * added as hull vertices
     */
    protected AbstractConvexHullGenerator2D(final boolean includeCollinearPoints) {
        this(includeCollinearPoints, DEFAULT_TOLERANCE);
    }

    /**
     * Simple constructor.
     *
     * @param includeCollinearPoints indicates if collinear points on the hull shall be
     * added as hull vertices
     * @param tolerance tolerance below which points are considered identical
     */
    protected AbstractConvexHullGenerator2D(final boolean includeCollinearPoints, final double tolerance) {
        this.includeCollinearPoints = includeCollinearPoints;
        this.tolerance = tolerance;
    }

    /**
     * Get the tolerance below which points are considered identical.
     * @return the tolerance below which points are considered identical
     */
    public double getTolerance() {
        return tolerance;
    }

    /**
     * Returns if collinear points on the hull will be added as hull vertices.
     * @return {@code true} if collinear points are added as hull vertices, or {@code false}
     * if only extreme points are present.
     */
    public boolean isIncludeCollinearPoints() {
        return includeCollinearPoints;
    }

    /** {@inheritDoc} */
    public ConvexHull2D generate(final Collection<Vector2D> points)
            throws NullArgumentException, ConvergenceException {
        // check for null points
        MathUtils.checkNotNull(points);

        Collection<Vector2D> hullVertices = null;
        if (points.size() < 2) {
            hullVertices = points;
        } else {
            hullVertices = findHullVertices(points);
        }

        try {
            return new ConvexHull2D(hullVertices.toArray(new Vector2D[hullVertices.size()]),
                                    tolerance);
        } catch (MathIllegalArgumentException e) {
            // the hull vertices may not form a convex hull if the tolerance value is to large
            throw new ConvergenceException();
        }
    }

    /**
     * Find the convex hull vertices from the set of input points.
     * @param points the set of input points
     * @return the convex hull vertices in CCW winding
     */
    protected abstract Collection<Vector2D> findHullVertices(Collection points);

}

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