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** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
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** This file is part of the QtPositioning module of the Qt Toolkit.
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#include "qgeoprojection_p.h"

#include "qgeocoordinate.h"

#include <qnumeric.h>

#include <cmath>

#include "qdoublevector2d_p.h"
#include "qdoublevector3d_p.h"

QT_BEGIN_NAMESPACE

QDoubleVector2D QGeoProjection::coordToMercator(const QGeoCoordinate &coord)
{
    const double pi = M_PI;

    double lon = coord.longitude() / 360.0 + 0.5;

    double lat = coord.latitude();
    lat = 0.5 - (std::log(std::tan((pi / 4.0) + (pi / 2.0) * lat / 180.0)) / pi) / 2.0;
    lat = qMax(0.0, lat);
    lat = qMin(1.0, lat);

    return QDoubleVector2D(lon, lat);
}

double QGeoProjection::realmod(const double a, const double b)
{
    quint64 div = static_cast<quint64>(a / b);
    return a - static_cast<double>(div) * b;
}

QGeoCoordinate QGeoProjection::mercatorToCoord(const QDoubleVector2D &mercator)
{
    const double pi = M_PI;

    double fx = mercator.x();
    double fy = mercator.y();

    if (fy < 0.0)
        fy = 0.0;
    else if (fy > 1.0)
        fy = 1.0;

    double lat;

    if (fy == 0.0)
        lat = 90.0;
    else if (fy == 1.0)
        lat = -90.0;
    else
        lat = (180.0 / pi) * (2.0 * std::atan(std::exp(pi * (1.0 - 2.0 * fy))) - (pi / 2.0));

    double lng;
    if (fx >= 0) {
        lng = realmod(fx, 1.0);
    } else {
        lng = realmod(1.0 - realmod(-1.0 * fx, 1.0), 1.0);
    }

    lng = lng * 360.0 - 180.0;

    return QGeoCoordinate(lat, lng, 0.0);
}

QGeoCoordinate QGeoProjection::coordinateInterpolation(const QGeoCoordinate &from, const QGeoCoordinate &to, qreal progress)
{
    QDoubleVector2D s = QGeoProjection::coordToMercator(from);
    QDoubleVector2D e = QGeoProjection::coordToMercator(to);

    double x = s.x();

    if (0.5 < qAbs(e.x() - s.x())) {
        // handle dateline crossing
        double ex = e.x();
        double sx = s.x();
        if (ex < sx)
            sx -= 1.0;
        else if (sx < ex)
            ex -= 1.0;

        x = (1.0 - progress) * sx + progress * ex;

        if (!qFuzzyIsNull(x) && (x < 0.0))
            x += 1.0;

    } else {
        x = (1.0 - progress) * s.x() + progress * e.x();
    }

    double y = (1.0 - progress) * s.y() + progress * e.y();

    QGeoCoordinate result = QGeoProjection::mercatorToCoord(QDoubleVector2D(x, y));
    result.setAltitude((1.0 - progress) * from.altitude() + progress * to.altitude());

    return result;
}

QT_END_NAMESPACE