001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.geometry.core;
018
019import java.util.Collection;
020import java.util.List;
021import java.util.stream.Collectors;
022
023/** This interface defines mappings between a space and one of its subspaces.
024
025 * <p>Subspaces are the lower-dimension subsets of a space. For example,
026 * in an n-dimension space, the subspaces are the (n-1) dimension space,
027 * the (n-2) dimension space, and so on. This interface can be used regardless
028 * of the difference in number of dimensions between the space and the target
029 * subspace. For example, a line in 3D Euclidean space can use this interface
030 * to map directly from 3D Euclidean space to 1D Euclidean space (ie, the location
031 * along the line).</p>
032 *
033 * @param <P> Point type defining the embedding space.
034 * @param <S> Point type defining the embedded subspace.
035 */
036public interface Embedding<P extends Point<P>, S extends Point<S>> {
037
038    /** Transform a space point into a subspace point.
039     * @param pt n-dimension point of the space
040     * @return lower-dimension point of the subspace corresponding to
041     *      the specified space point
042     * @see #toSpace
043     */
044    S toSubspace(P pt);
045
046    /** Transform a collection of space points into subspace points.
047     * @param pts collection of n-dimension points to transform
048     * @return collection of transformed lower-dimension points.
049     * @see #toSubspace(Point)
050     */
051    default List<S> toSubspace(final Collection<P> pts) {
052        return pts.stream().map(this::toSubspace).collect(Collectors.toList());
053    }
054
055    /** Transform a subspace point into a space point.
056     * @param pt lower-dimension point of the subspace
057     * @return n-dimension point of the space corresponding to the
058     *      specified subspace point
059     * @see #toSubspace(Point)
060     */
061    P toSpace(S pt);
062
063    /** Transform a collection of subspace points into space points.
064     * @param pts collection of lower-dimension points to transform
065     * @return collection of transformed n-dimension points.
066     * @see #toSpace(Point)
067     */
068    default List<P> toSpace(final Collection<S> pts) {
069        return pts.stream().map(this::toSpace).collect(Collectors.toList());
070    }
071}