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This geoLatte-geom library offers a geometry model that conforms to the OGC Simple Features for SQL specification.
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/*
 * This file is part of the GeoLatte project.
 *
 *     GeoLatte 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 3 of the License, or
 *     (at your option) any later version.
 *
 *     GeoLatte 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 GeoLatte.  If not, see .
 *
 * Copyright (C) 2010 - 2011 and Ownership of code is shared by:
 * Qmino bvba - Romeinsestraat 18 - 3001 Heverlee  (http://www.qmino.com)
 * Geovise bvba - Generaal Eisenhowerlei 9 - 2140 Antwerpen (http://www.geovise.com)
 */

package org.geolatte.geom;

import org.geolatte.geom.crs.CoordinateReferenceSystem;

/**
 * A LineString is a 1-dimensional Geometry consisting of the LineSegments defined by
 * consecutive pairs of Points of a PointSequence.
 *
 * @author Karel Maesen, Geovise BVBA, 2011
 */
public class LineString extends Geometry
 implements Linear
, Simple {

    public LineString(CoordinateReferenceSystem
 crs) {
        super(crs);
    }

    /**
     * This constructor has been added to speed up object creation of LinearRings
     *
     * @param base
     */
    protected LineString(LineString
 base) {
        super(base.getPositions(), base.getCoordinateReferenceSystem());
    }

    /**
     * Constructs a LineString from the specified positions
     * and CoordinateReferenceSystem.
     *
     * @param positions the {@code PositionSequence} that determines the geometry
     * @params crs the  {@code CoordinateReferenceSystem} for the geometry
     * @throws IllegalArgumentException if the passed PointSequence is non-empty and of size less than 2
     */
    public LineString(PositionSequence
 positions, CoordinateReferenceSystem
 crs) {
        super(positions, crs);
        if (positions.size() != 0 && positions.size() < 2) {
            throw new IllegalArgumentException("Require at least two points for a linestring");
        }
    }


    /**
     * Returns the first Position of this LineString.
     *
     * @return the first Position of this LineString.
     */
    public P getStartPosition() {
        return getPositionN(0);
    }


    /**
     * Returns the last Position of this LineString.
     *
     * @return the last Position of this LineString.
     */
    public P getEndPosition() {
        return getPositionN(getNumPositions() - 1);
    }

    /**
     * Checks whether this LineString is closed, i.e. the first Point equals the last.
     *
     * @return true if this LineString is closed.
     */
    public boolean isClosed() {
        return !isEmpty() && getStartPosition().equals(getEndPosition());
    }

    /**
     * Checks whether this LineString is a ring, i.e. is closed and non-empty.
     *
     * 
Note that this implementation allows rings thate are non-simple.
     *
     * @return true if this LineString is a ring.
     */
    public boolean isRing() {
        return !isEmpty() && isClosed();
    }

    @Override
    public int getDimension() {
        return 1;
    }

    @Override
    public GeometryType getGeometryType() {
        return GeometryType.LINESTRING;
    }

    @Override
    public void accept(GeometryVisitor visitor) {
        visitor.visit(this);
    }

    /**
     * Returns the {@code LineSegments} that define this instance.
     *
     * @return an Iterable of this instance's {@code LineSegment}s
     */
    Iterable> lineSegments() {
        return new LineSegments(getPositions());
    }

    @Override
    @SuppressWarnings("unchecked")
    public  LineString as(Class castToType){
        checkCast(castToType);
        return (LineString)this;
    }

}