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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 - 2012 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;

/**
 * A GeometryEquality that considers two Geometrys to be equal iff one of these conditions is
 * satisfied:
 * 
 *      both have the same type, coordinate reference system and consist of the same Points.
 *      both are empty
 * 
 *
 * Point equality is determined by the {@link PositionEquality} instance that is passed to the constructor. In
 * case of the default no-args constructor, {@link ExactPositionEquality} is used.
 *
 * @author Karel Maesen, Geovise BVBA
 *         creation-date: 4/25/12
 */
public class GeometryPositionEquality implements GeometryEquality {


    private final PositionSequenceEquality pointSeqEq;

    /**
     * Constructs an instance that uses the specified PositionEquality to determine
     * whether the Geometrys have the same Positionss.
     *
     * @param pointEq
     */
    public GeometryPositionEquality(PositionEquality pointEq) {
        this.pointSeqEq = new PositionSequencePositionEquality(pointEq);
    }

    /**
     * Constructs an instance that uses {@code ExactPositionEquality} to determine
     * whether the Geometrys have the same Positionss.
     */
    public GeometryPositionEquality() {
        ExactPositionEquality pointEquality = new ExactPositionEquality();
        this.pointSeqEq = new PositionSequencePositionEquality(pointEquality);
    }

    //FIXME - provide a means to also inject an PositionSequenceEquality, e.g.
    // for rings equal except one is shifted n positions w.r.t the other.


    /**
     * {@inheritDoc}
     */
    @Override
    public  boolean equals(Geometry
 first, Geometry
 second) {
        if (first == second) return true;
        if (first == null || second == null) return false;
        if (first.isEmpty() && second.isEmpty()) return true;
        if (first.isEmpty() || second.isEmpty()) return false;
        if (! first.getCoordinateReferenceSystem().equals(second.getCoordinateReferenceSystem())) return false;
        if (first.getGeometryType() != second.getGeometryType()) return false;
        if (first instanceof AbstractGeometryCollection) {
            assert(second instanceof AbstractGeometryCollection);
            return equals((AbstractGeometryCollection)first, (AbstractGeometryCollection)second);
        }
        if (first instanceof Polygon) {
            assert(second instanceof Polygon);
            return equals((Polygon
)first, (Polygon
)second);
        }
        return pointSeqEq.equals(first.getPositions(), second.getPositions());
    }

    private 
 boolean equals (Polygon
 first, Polygon second){
        if (first.getNumInteriorRing() != second.getNumInteriorRing()) return false;
        if (!equals(first.getExteriorRing(), second.getExteriorRing())) return false;
        for (int i = 0; i < first.getNumInteriorRing(); i++) {
            if (!equals(first.getInteriorRingN(i), second.getInteriorRingN(i))) return false;
        }
        return true;
    }

    private boolean equals(AbstractGeometryCollection first, AbstractGeometryCollection second) {
        if (first.getNumGeometries() != second.getNumGeometries()) return false;
        for (int i = 0; i < first.getNumGeometries(); i++) {
            if (! equals(first.getGeometryN(i), second.getGeometryN(i))) return false;
        }
        return true;
    }
}