/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2000-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library 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;
 *    version 2.1 of the License.
 *
 *    This library 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.
 *
 *    This package contains formulas from the PROJ package of USGS.
 *    USGS's work is fully acknowledged here. This derived work has
 *    been relicensed under LGPL with Frank Warmerdam's permission.
 */
package org.geotools.referencing.operation.projection;

import java.awt.geom.Point2D;
import org.opengis.parameter.ParameterNotFoundException;
import org.opengis.parameter.ParameterValueGroup;
import org.geotools.resources.i18n.ErrorKeys;

import static java.lang.Math.*;


/**
 * The equatorial case of the {@link Orthographic} projection. This is a
 * simplification of the oblique case for {@link #latitudeOfOrigin} == 0.0.
 * Only the spherical form is given here.
 *
 * @todo this code is identical to the oblique except for 6 lines.
 *       It could be moved to the oblique with an isEquatorial flag.
 *
 * @since 2.4
 *
 *
 * @source $URL$
 * @version $Id$
 * @author Rueben Schulz
 */
public class EquatorialOrthographic extends ObliqueOrthographic {
    /**
     * For cross-version compatibility.
     */
    private static final long serialVersionUID = 1093901743907259987L;

    /**
     * Maximum difference allowed when comparing real numbers.
     */
    private static final double EPSILON = 1E-6;

    /**
     * Constructs an equatorial orthographic projection.
     *
     * @param  parameters The parameter values in standard units.
     * @throws ParameterNotFoundException if a mandatory parameter is missing.
     */
    protected EquatorialOrthographic(final ParameterValueGroup parameters)
            throws ParameterNotFoundException
    {
        super(parameters);
        ensureLatitudeEquals(Provider.LATITUDE_OF_ORIGIN, latitudeOfOrigin, 0);
        latitudeOfOrigin = 0.0;
    }

    /**
     * Transforms the specified (<var>&lambda;</var>,<var>&phi;</var>) coordinates
     * (units in radians) and stores the result in {@code ptDst} (linear distance
     * on a unit sphere).
     */
    @Override
    protected Point2D transformNormalized(double x, double y, Point2D ptDst)
            throws ProjectionException
    {
        // Compute using oblique formulas, for comparaison later.
        assert (ptDst = super.transformNormalized(x, y, ptDst)) != null;
        final double cosphi = cos(y);
        final double coslam = cos(x);
        if (cosphi * coslam < -EPSILON) {
            throw new ProjectionException(ErrorKeys.POINT_OUTSIDE_HEMISPHERE);
        }
        y = sin(y);
        x = cosphi * sin(x);

        assert checkTransform(x, y, ptDst);
        if (ptDst != null) {
            ptDst.setLocation(x,y);
            return ptDst;
        }
        return new Point2D.Double(x,y);
    }

    /**
     * Transforms the specified (<var>x</var>,<var>y</var>) coordinates
     * and stores the result in {@code ptDst}.
     */
    @Override
    protected Point2D inverseTransformNormalized(double x, double y, Point2D ptDst)
            throws ProjectionException
    {
        // Compute using oblique formulas, for comparaison later.
        assert (ptDst = super.inverseTransformNormalized(x, y, ptDst)) != null;
        final double rho = hypot(x, y);
        double sinc = rho;
        if (sinc > 1.0) {
            if ((sinc - 1.0) > EPSILON) {
                throw new ProjectionException(ErrorKeys.POINT_OUTSIDE_HEMISPHERE);
            }
            sinc = 1.0;
        }
        final double cosc = sqrt(1.0 - sinc * sinc); /* in this range OK */
        if (rho <= EPSILON) {
            y = latitudeOfOrigin;
            x = 0.0;
        } else {
            double phi = y * sinc / rho;
            x *= sinc;
            y = cosc * rho;

            // begin sinchk
            if (abs(phi) >= 1.0) {
                phi = (phi < 0.0) ? -PI/2.0 : PI/2.0;
            } else {
                phi = asin(phi);
            }
            // end sinchk

            if (y == 0.0) {
                if (x == 0.0) {
                    x = 0.0;
                } else {
                    x = (x < 0.0) ? -PI/2.0 : PI/2.0;
                }
            } else {
                x = atan2(x, y);
            }
            y = phi;
        }
        assert checkInverseTransform(x, y, ptDst);
        if (ptDst != null) {
            ptDst.setLocation(x,y);
            return ptDst;
        }
        return new Point2D.Double(x,y);
    }
}