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.datum;
019
020import java.util.Map;
021import org.opengis.annotation.UML;
022
023import static org.opengis.annotation.Obligation.*;
024import static org.opengis.annotation.Specification.*;
025
026
027/**
028 * Position, scale and orientation of a geocentric Cartesian 3D coordinate system relative to the planet.
029 * It may also identify a defined ellipsoid (or sphere) that approximates the shape of the planet
030 * and which is centred on and aligned to this geocentric coordinate system.
031 *
032 * @author  OGC Topic 2 (for abstract model and documentation)
033 * @author  Martin Desruisseaux (IRD, Geomatys)
034 * @version 3.1
035 * @since   1.0
036 *
037 * @see Ellipsoid
038 * @see PrimeMeridian
039 *
040 * @see DatumAuthorityFactory#createGeodeticDatum(String)
041 * @see DatumFactory#createGeodeticDatum(Map, Ellipsoid, PrimeMeridian)
042 */
043@UML(identifier="GeodeticReferenceFram", specification=ISO_19111)
044public interface GeodeticDatum extends Datum {
045    /**
046     * Returns an approximation of the surface of the geoid.
047     * Because of the area for which the approximation is valid
048     * — traditionally regionally, but with the advent of satellite positioning often globally —
049     * the ellipsoid is typically associated with Geographic and Projected <abbr>CRS</abbr>s.
050     *
051     * <h4>Obligation</h4>
052     * If the <abbr>CRS</abbr> using this frame is associated to an {@link org.opengis.referencing.cs.EllipsoidalCS},
053     * then the ellipsoid is mandatory. This is the case of all {@link org.opengis.referencing.crs.GeographicCRS}.
054     * But if the <abbr>CRS</abbr> is associated to a {@link org.opengis.referencing.cs.CartesianCS} or
055     * {@link org.opengis.referencing.cs.SphericalCS}, then the ellipsoid is optional.
056     * However, if there is a recommended reference ellipsoid for the reference frame
057     * then it is advised to return that ellipsoid.
058     *
059     * @return the approximation of the surface of the geoid, or {@code null} if unspecified.
060     *         A non-null value is mandatory when this frame is used with ellipsoidal coordinate systems,
061     *         and recommended for all other cases.
062     */
063    @UML(identifier="ellipsoid", obligation=CONDITIONAL, specification=ISO_19111)
064    Ellipsoid getEllipsoid();
065
066    /**
067     * Returns the origin from which longitude values are specified.
068     * Most geodetic reference frames use Greenwich as their prime meridian.
069     *
070     * @return the origin from which longitude values are specified.
071     */
072    @UML(identifier="primeMeridian", obligation=MANDATORY, specification=ISO_19111)
073    PrimeMeridian getPrimeMeridian();
074}