001/*
002 *    GeoAPI - Java interfaces for OGC/ISO standards
003 *    Copyright © 2003-2023 Open Geospatial Consortium, Inc.
004 *    http://www.geoapi.org
005 *
006 *    Licensed under the Apache License, Version 2.0 (the "License");
007 *    you may not use this file except in compliance with the License.
008 *    You may obtain a copy of the License at
009 *
010 *        http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *    Unless required by applicable law or agreed to in writing, software
013 *    distributed under the License is distributed on an "AS IS" BASIS,
014 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 *    See the License for the specific language governing permissions and
016 *    limitations under the License.
017 */
018package org.opengis.referencing.crs;
019
020import java.util.Map;
021import org.opengis.referencing.cs.EllipsoidalCS;
022import org.opengis.referencing.datum.Ellipsoid;
023import org.opengis.referencing.datum.GeodeticDatum;
024import org.opengis.referencing.datum.DatumEnsemble;
025import org.opengis.annotation.UML;
026
027import static org.opengis.annotation.Obligation.*;
028import static org.opengis.annotation.Specification.*;
029
030
031/**
032 * A 2- or 3-dimensional <abbr>CRS</abbr> based on an ellipsoidal approximation of the geoid.
033 * This provides an accurate representation of the geometry of geographic features for a large portion of the planet's surface.
034 * A 2D geographic <abbr>CRS</abbr> is used when positions of features are described on the surface of the reference ellipsoid.
035 * A 3D geographic <abbr>CRS</abbr> is used when positions are described on, above or below the reference ellipsoid.
036 *
037 * <p>A geographic <abbr>CRS</abbr> is not suitable for mapmaking on a planar surface,
038 * because it describes geometry on a curved surface.
039 * It is impossible to represent such geometry in a Euclidean plane without introducing distortions.
040 * The need to control these distortions has given rise to the development of {@link ProjectedCRS}s.</p>
041 *
042 * <p>The {@link GeodeticDatum} associated to this <abbr>CRS</abbr> must have an {@link Ellipsoid}.
043 * I.e., the ellipsoid is generally optional but become mandatory in the context of {@code GeographicCRS}.</p>
044 *
045 * <h2>Permitted coordinate systems</h2>
046 * This type of <abbr>CRS</abbr> can be used with coordinate systems of type {@link EllipsoidalCS} only.
047 *
048 * @author  OGC Topic 2 (for abstract model and documentation)
049 * @author  Martin Desruisseaux (IRD, Geomatys)
050 * @version 3.1
051 * @since   1.0
052 *
053 * @see CRSAuthorityFactory#createGeographicCRS(String)
054 * @see CRSFactory#createGeographicCRS(Map, GeodeticDatum, DatumEnsemble, EllipsoidalCS)
055 */
056@UML(identifier="GeographicCRS", specification=ISO_19111)
057public interface GeographicCRS extends GeodeticCRS {
058    /**
059     * Returns the coordinate system, which shall be ellipsoidal.
060     *
061     * @return the ellipsoidal coordinate system.
062     */
063    @Override
064    @UML(identifier="coordinateSystem", obligation=MANDATORY, specification=ISO_19111)
065    EllipsoidalCS getCoordinateSystem();
066}