agoss94 commented on code in PR #218: URL: https://github.com/apache/commons-geometry/pull/218#discussion_r1269917506
########## commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/twod/hull/ConvexHull2D.java: ########## @@ -0,0 +1,469 @@ +/* + * 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.geometry.euclidean.twod.hull; + +import java.util.ArrayList; +import java.util.Collection; +import java.util.Collections; +import java.util.Iterator; +import java.util.List; + +import org.apache.commons.geometry.core.ConvexHull; +import org.apache.commons.geometry.euclidean.EuclideanCollections; +import org.apache.commons.geometry.euclidean.twod.ConvexArea; +import org.apache.commons.geometry.euclidean.twod.Lines; +import org.apache.commons.geometry.euclidean.twod.Vector2D; +import org.apache.commons.geometry.euclidean.twod.path.LinePath; +import org.apache.commons.numbers.core.Precision; + +/** + * This class represents a convex hull in two-dimensional Euclidean space. + */ +public final class ConvexHull2D implements ConvexHull<Vector2D> { + + /** Vertices for the convex hull, in order. */ + private final List<Vector2D> vertices; + + /** Polyline path for the convex hull. */ + private final LinePath path; + + /** Simple constructor; no validation is performed. + * @param vertices the vertices of the convex hull; callers are responsible for ensuring that + * the given vertices are in order, unique, and define a convex hull. + * @param precision precision context used to compare floating point numbers + */ + ConvexHull2D(final Collection<Vector2D> vertices, final Precision.DoubleEquivalence precision) { + this.vertices = Collections.unmodifiableList(new ArrayList<>(vertices)); + this.path = buildHullPath(vertices, precision); + } + + /** {@inheritDoc} */ + @Override + public List<Vector2D> getVertices() { + return vertices; + } + + /** Get a path defining the convex hull. The path will contain + * <ul> + * <li>zero segments if the hull consists of only a single point,</li> + * <li>one segment if the hull consists of two points,</li> + * <li>three or more segments defining a closed loop if the hull consists of more than + * two non-collinear points.</li> + * </ul> + * @return polyline path defining the convex hull + */ + public LinePath getPath() { + return path; + } + + /** {@inheritDoc} */ + @Override + public ConvexArea getRegion() { + return path.isClosed() ? + ConvexArea.convexPolygonFromPath(path) : + null; + } + + /** {@inheritDoc} */ + @Override + public String toString() { + final StringBuilder sb = new StringBuilder(); + sb.append(getClass().getSimpleName()) + .append("[vertices= ") + .append(getVertices()) + .append(']'); + + return sb.toString(); + } + + /** Build a polyline representing the path for a convex hull. + * @param vertices convex hull vertices + * @param precision precision context used to compare floating point values + * @return path for the convex hull defined by the given vertices + */ + private static LinePath buildHullPath(final Collection<Vector2D> vertices, + final Precision.DoubleEquivalence precision) { + if (vertices.size() < 2) { + return LinePath.empty(); + } + + final boolean closeLoop = vertices.size() > 2; + + return LinePath.builder(precision) + .appendVertices(vertices) + .build(closeLoop); + } + + /** Class used to build convex hulls. The builder is based on the Akl-Toussaint + * heuristic to construct the hull. The heuristic is based on the idea of a + * convex quadrilateral, which is formed by four points with the lowest and + * highest x / y coordinates. Any point that lies inside this quadrilateral can + * not be part of the convex hull and can thus be safely discarded before + * generating the convex hull itself. + * <p> + * The complexity of the operation is O(n), and may greatly improve the time it + * takes to construct the convex hull afterwards, depending on the point + * distribution. + * + * @see <a href= + * "http://en.wikipedia.org/wiki/Convex_hull_algorithms#Akl-Toussaint_heuristic";> + * Akl-Toussaint heuristic (Wikipedia)</a> + */ + public static final class Builder { + + /** Corner of triangle with minimal x coordinate. */ Review Comment: Yes, that should obviously mean quadrilateral. -- This is an automated message from the Apache Git Service. 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