001// License: GPL. For details, see LICENSE file.
002package org.openstreetmap.josm.data.projection.proj;
003
004import static org.openstreetmap.josm.tools.I18n.tr;
005
006import org.openstreetmap.josm.data.Bounds;
007import org.openstreetmap.josm.data.projection.ProjectionConfigurationException;
008
009/**
010 * Mercator Cylindrical Projection. The parallels and the meridians are straight lines and
011 * cross at right angles; this projection thus produces rectangular charts. The scale is true
012 * along the equator (by default) or along two parallels equidistant of the equator (if a scale
013 * factor other than 1 is used). This projection is used to represent areas close to the equator.
014 * It is also often used for maritime navigation because all the straight lines on the chart are
015 * <em>loxodrome</em> lines, i.e. a ship following this line would keep a constant azimuth on its
016 * compass.
017 * <p>
018 * This implementation handles both the 1 and 2 stardard parallel cases.
019 * For 1 SP (EPSG code 9804), the line of contact is the equator.
020 * For 2 SP (EPSG code 9805) lines of contact are symmetrical
021 * about the equator.
022 * <p>
023 * This class has been derived from the implementation of the Geotools project;
024 * git 8cbf52d, org.geotools.referencing.operation.projection.Mercator
025 * at the time of migration.
026 * <p>
027 * <b>References:</b>
028 * <ul>
029 *   <li>John P. Snyder (Map Projections - A Working Manual,<br>
030 *       U.S. Geological Survey Professional Paper 1395, 1987)</li>
031 *   <li>"Coordinate Conversions and Transformations including Formulas",<br>
032 *       EPSG Guidence Note Number 7, Version 19.</li>
033 * </ul>
034 *
035 * @author André Gosselin
036 * @author Martin Desruisseaux (PMO, IRD)
037 * @author Rueben Schulz
038 * @author Simone Giannecchini
039 *
040 * @see <A HREF="http://mathworld.wolfram.com/MercatorProjection.html">Mercator projection on MathWorld</A>
041 * @see <A HREF="http://www.remotesensing.org/geotiff/proj_list/mercator_1sp.html">"mercator_1sp" on RemoteSensing.org</A>
042 * @see <A HREF="http://www.remotesensing.org/geotiff/proj_list/mercator_2sp.html">"mercator_2sp" on RemoteSensing.org</A>
043 */
044public class Mercator extends AbstractProj implements IScaleFactorProvider {
045    /**
046     * Maximum difference allowed when comparing real numbers.
047     */
048    private static final double EPSILON = 1E-6;
049
050    protected double scaleFactor;
051
052    @Override
053    public String getName() {
054        return tr("Mercator");
055    }
056
057    @Override
058    public String getProj4Id() {
059        return "merc";
060    }
061
062    @Override
063    public void initialize(ProjParameters params) throws ProjectionConfigurationException {
064        super.initialize(params);
065        scaleFactor = 1;
066        if (params.lat_ts != null) {
067            /*
068             * scaleFactor is not a parameter in the 2 SP case and is computed from
069             * the standard parallel.
070             */
071            double standardParallel = Math.toRadians(params.lat_ts);
072            if (spherical) {
073                scaleFactor *= Math.cos(standardParallel);
074            } else {
075                scaleFactor *= msfn(Math.sin(standardParallel), Math.cos(standardParallel));
076            }
077        }
078        /*
079         * A correction that allows us to employs a latitude of origin that is not
080         * correspondent to the equator. See Snyder and al. for reference, page 47.
081         */
082        if (params.lat0 != null) {
083            final double lat0 = Math.toRadians(params.lat0);
084            final double sinPhi = Math.sin(lat0);
085            scaleFactor *= (Math.cos(lat0) / (Math.sqrt(1 - e2 * sinPhi * sinPhi)));
086        }
087    }
088
089    @Override
090    public double[] project(double y, double x) {
091        if (Math.abs(y) > (Math.PI/2 - EPSILON)) {
092            return new double[] {0, 0}; // this is an error and should be handled somehow
093        }
094        if (spherical) {
095            y = Math.log(Math.tan(Math.PI/4 + 0.5*y));
096        } else {
097            y = -Math.log(tsfn(y, Math.sin(y)));
098        }
099        return new double[] {x, y};
100    }
101
102    @Override
103    public double[] invproject(double x, double y) {
104        if (spherical) {
105            y = Math.PI/2 - 2.0*Math.atan(Math.exp(-y));
106        } else {
107            y = Math.exp(-y);
108            y = cphi2(y);
109        }
110        return new double[] {y, x};
111    }
112
113    @Override
114    public Bounds getAlgorithmBounds() {
115        return new Bounds(-89, -180, 89, 180, false);
116    }
117
118    @Override
119    public double getScaleFactor() {
120        return scaleFactor;
121    }
122}