LineConvexSubset.java

/*
 * 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
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 *
 *      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,
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 * See the License for the specific language governing permissions and
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package org.apache.commons.geometry.euclidean.twod;

import java.util.Collections;
import java.util.List;

import org.apache.commons.geometry.core.Transform;
import org.apache.commons.geometry.core.partitioning.Hyperplane;
import org.apache.commons.geometry.core.partitioning.HyperplaneConvexSubset;
import org.apache.commons.geometry.core.partitioning.Split;
import org.apache.commons.geometry.euclidean.oned.Interval;

/** Class representing a convex subset of a line in 2D Euclidean space. Instances
 * need not be finite, in which case the start or end point (or both) will be null.
 * Line segments and rays are examples of convex line subsets.
 * @see Lines
 */
public abstract class LineConvexSubset extends LineSubset implements HyperplaneConvexSubset<Vector2D> {

    /** Construct a new instance for the given line.
     * @param line line containing this line subset
     */
    LineConvexSubset(final Line line) {
        super(line);
    }

    /** {@inheritDoc} */
    @Override
    public List<LineConvexSubset> toConvex() {
        return Collections.singletonList(this);
    }

    /** {@inheritDoc}
     *
     * <p>This method always returns {@code false}.</p>
     */
    @Override
    public boolean isEmpty() {
        return false;
    }

    /** Get the start point for the subset.
     * @return the start point for the subset, or null if no start point exists
     */
    public abstract Vector2D getStartPoint();

    /** Get the 1D start location of the subset or {@link Double#NEGATIVE_INFINITY} if
     * no start location exists.
     * @return the 1D start location of the subset or {@link Double#NEGATIVE_INFINITY} if
     *      no start location exists.
     */
    public abstract double getSubspaceStart();

    /** Get the end point for the subset.
     * @return the end point for the subset, or null if no end point exists.
     */
    public abstract Vector2D getEndPoint();

    /** Get the 1D end location of the subset or {@link Double#POSITIVE_INFINITY} if
     * no end location exists.
     * @return the 1D end location of the subset or {@link Double#POSITIVE_INFINITY} if
     *      no end location exists
     */
    public abstract double getSubspaceEnd();

    /** {@inheritDoc} */
    @Override
    public Interval getSubspaceRegion() {
        final double start = getSubspaceStart();
        final double end = getSubspaceEnd();

        return Interval.of(start, end, getPrecision());
    }

    /** Get the 1D interval for the region. This method is an alias for {@link #getSubspaceRegion()}.
     * @return the 1D interval for the region.
     */
    public Interval getInterval() {
        return getSubspaceRegion();
    }

    /** {@inheritDoc} */
    @Override
    public Split<LineConvexSubset> split(final Hyperplane<Vector2D> splitter) {
        final Line thisLine = getLine();
        final Line splitterLine = (Line) splitter;

        final Vector2D intersection = splitterLine.intersection(thisLine);
        if (intersection == null) {
            return getNonIntersectingSplitResult(splitterLine, this);
        }
        return splitOnIntersection(splitterLine, intersection);
    }

    /** {@inheritDoc} */
    @Override
    public Vector2D closest(final Vector2D pt) {
        final Line line = getLine();
        final double abscissa = line.abscissa(pt);

        return line.toSpace(closestAbscissa(abscissa));
    }

    /** {@inheritDoc} */
    @Override
    public abstract LineConvexSubset transform(Transform<Vector2D> transform);

    /** {@inheritDoc} */
    @Override
    public abstract LineConvexSubset reverse();

    /** Get the closest value in the subspace region to the given abscissa.
     * @param abscissa input abscissa
     * @return the closest value in the subspace region to the given abscissa
     */
    abstract double closestAbscissa(double abscissa);

    /** Split this instance using the given splitter line and intersection point.
     * @param splitter splitter line
     * @param intersection intersection point between the splitter line and the line
     *      for this instance
     * @return the result of splitting this instance with the given splitter line and intersection
     *      point
     */
    abstract Split<LineConvexSubset> splitOnIntersection(Line splitter, Vector2D intersection);
}