MercatorProjection.cpp

// SPDX-License-Identifier: LGPL-2.1-or-later
//
// SPDX-FileCopyrightText: 2007-2008 Inge Wallin <ingwa@kde.org>
// SPDX-FileCopyrightText: 2007-2012 Torsten Rahn <rahn@kde.org>
//
 
// Local
#include "MercatorProjection.h"
 
// Marble
#include "GeoDataLatLonAltBox.h"
#include "ViewportParams.h"
 
#include "MarbleMath.h"
 
#include <QIcon>
 
using namespace Marble;
 
MercatorProjection::MercatorProjection()
    : CylindricalProjection()
    , m_lastCenterLat(200.0)
    , m_lastCenterLatInv(0.0)
{
    setMinLat(minValidLat());
    setMaxLat(maxValidLat());
}
 
MercatorProjection::~MercatorProjection() = default;
 
QString MercatorProjection::name() const
{
    return QObject::tr("Mercator");
}
 
QString MercatorProjection::description() const
{
    return QObject::tr("<p><b>Mercator Projection</b></p><p>Applications: popular standard map projection for navigation.</p>");
}
 
QIcon MercatorProjection::icon() const
{
    return QIcon(QStringLiteral(":/icons/map-mercator.png"));
}
 
qreal MercatorProjection::maxValidLat() const
{
    // This is the max value where gd( lat ) is defined.
    return +85.05113 * DEG2RAD;
}
 
qreal MercatorProjection::minValidLat() const
{
    // This is the min value where gd( lat ) is defined.
    return -85.05113 * DEG2RAD;
}
 
bool MercatorProjection::screenCoordinates(const GeoDataCoordinates &geopoint, const ViewportParams *viewport, qreal &x, qreal &y, bool &globeHidesPoint) const
{
    globeHidesPoint = false;
    qreal lon;
    qreal originalLat;
 
    geopoint.geoCoordinates(lon, originalLat);
    qreal const lat = qBound(minLat(), originalLat, maxLat());
    const bool isLatValid = lat == originalLat;
 
    // Convenience variables
    int radius = viewport->radius();
    auto width = (qreal)(viewport->width());
    auto height = (qreal)(viewport->height());
 
    qreal rad2Pixel = 2 * radius / M_PI;
 
    const qreal centerLon = viewport->centerLongitude();
    const qreal centerLat = viewport->centerLatitude();
    if (centerLat != m_lastCenterLat) {
        m_lastCenterLatInv = gdInv(centerLat);
        m_lastCenterLat = centerLat;
    }
 
    // Let (x, y) be the position on the screen of the placemark..
    x = (width / 2 + rad2Pixel * (lon - centerLon));
    y = (height / 2 - rad2Pixel * (gdInv(lat) - m_lastCenterLatInv));
 
    // Return true if the calculated point is inside the screen area,
    // otherwise return false.
    return isLatValid
        && ((0 <= y && y < height)
            && ((0 <= x && x < width) || (0 <= x - 4 * radius && x - 4 * radius < width) || (0 <= x + 4 * radius && x + 4 * radius < width)));
}
 
bool MercatorProjection::screenCoordinates(const GeoDataCoordinates &coordinates,
                                           const ViewportParams *viewport,
                                           qreal *x,
                                           qreal &y,
                                           int &pointRepeatNum,
                                           const QSizeF &size,
                                           bool &globeHidesPoint) const
{
    pointRepeatNum = 0;
    // On flat projections the observer's view onto the point won't be
    // obscured by the target planet itself.
    globeHidesPoint = false;
 
    // Convenience variables
    int radius = viewport->radius();
    auto width = (qreal)(viewport->width());
    auto height = (qreal)(viewport->height());
 
    // Let (itX, y) be the first guess for one possible position on screen..
    qreal itX;
    bool visible = screenCoordinates(coordinates, viewport, itX, y);
 
    // Make sure that the requested point is within the visible y range:
    if (0 <= y + size.height() / 2.0 && y < height + size.height() / 2.0) {
        // For the repetition case the same geopoint gets displayed on
        // the map many times.across the longitude.
 
        int xRepeatDistance = 4 * radius;
 
        // Finding the leftmost positive x value
        if (itX + size.width() / 2.0 >= xRepeatDistance) {
            const int repeatNum = (int)((itX + size.width() / 2.0) / xRepeatDistance);
            itX = itX - repeatNum * xRepeatDistance;
        }
        if (itX + size.width() / 2.0 < 0) {
            itX += xRepeatDistance;
        }
        // the requested point is out of the visible x range:
        if (itX > width + size.width() / 2.0) {
            return false;
        }
 
        // Now iterate through all visible x screen coordinates for the point
        // from left to right.
        int itNum = 0;
        while (itX - size.width() / 2.0 < width) {
            *x = itX;
            ++x;
            ++itNum;
            itX += xRepeatDistance;
        }
 
        pointRepeatNum = itNum;
 
        return visible;
    }
 
    // the requested point is out of the visible y range:
    return false;
}
 
bool MercatorProjection::geoCoordinates(const int x, const int y, const ViewportParams *viewport, qreal &lon, qreal &lat, GeoDataCoordinates::Unit unit) const
{
    const int radius = viewport->radius();
    Q_ASSERT(radius > 0);
 
    // Calculate translation of center point
    const qreal centerLon = viewport->centerLongitude();
    const qreal centerLat = viewport->centerLatitude();
 
    // Calculate how many pixel are being represented per radians.
    const float rad2Pixel = (qreal)(2 * radius) / M_PI;
    const qreal pixel2Rad = M_PI / (2 * radius);
 
    {
        const int halfImageWidth = viewport->width() / 2;
        const int xPixels = x - halfImageWidth;
        lon = xPixels * pixel2Rad + centerLon;
 
        while (lon > M_PI)
            lon -= 2 * M_PI;
        while (lon < -M_PI)
            lon += 2 * M_PI;
 
        if (unit == GeoDataCoordinates::Degree) {
            lon *= RAD2DEG;
        }
    }
 
    {
        const int halfImageHeight = viewport->height() / 2;
        const int yCenterOffset = (int)(asinh(tan(centerLat)) * rad2Pixel);
        const int yTop = halfImageHeight - 2 * radius + yCenterOffset;
        const int yBottom = yTop + 4 * radius;
        if (y >= yTop && y < yBottom) {
            lat = gd(((halfImageHeight + yCenterOffset) - y) * pixel2Rad);
 
            if (unit == GeoDataCoordinates::Degree) {
                lat *= RAD2DEG;
            }
 
            return true; // lat successfully calculated
        }
    }
 
    return false; // lat unchanged
}
 
GeoDataLatLonAltBox MercatorProjection::latLonAltBox(const QRect &screenRect, const ViewportParams *viewport) const
{
    qreal west;
    qreal north = 85 * DEG2RAD;
    geoCoordinates(screenRect.left(), screenRect.top(), viewport, west, north, GeoDataCoordinates::Radian);
 
    qreal east;
    qreal south = -85 * DEG2RAD;
    geoCoordinates(screenRect.right(), screenRect.bottom(), viewport, east, south, GeoDataCoordinates::Radian);
 
    // For the case where the whole viewport gets covered there is a
    // pretty dirty and generic detection algorithm:
    GeoDataLatLonAltBox latLonAltBox;
    latLonAltBox.setNorth(north, GeoDataCoordinates::Radian);
    latLonAltBox.setSouth(south, GeoDataCoordinates::Radian);
    latLonAltBox.setWest(west, GeoDataCoordinates::Radian);
    latLonAltBox.setEast(east, GeoDataCoordinates::Radian);
    latLonAltBox.setMinAltitude(-100000000.0);
    latLonAltBox.setMaxAltitude(100000000000000.0);
 
    // The remaining algorithm should be pretty generic for all kinds of
    // flat projections:
 
    // If the whole globe is visible we can easily calculate
    // analytically the lon-/lat- range.
    // qreal pitch = GeoDataPoint::normalizeLat( viewport->planetAxis().pitch() );
 
    int xRepeatDistance = 4 * viewport->radius();
    if (viewport->width() >= xRepeatDistance) {
        latLonAltBox.setWest(-M_PI);
        latLonAltBox.setEast(+M_PI);
    }
 
    return latLonAltBox;
}
 
bool MercatorProjection::mapCoversViewport(const ViewportParams *viewport) const
{
    int radius = viewport->radius();
    int height = viewport->height();
 
    // Calculate translation of center point
    const qreal centerLat = viewport->centerLatitude();
 
    // Calculate how many pixel are being represented per radians.
    const float rad2Pixel = (float)(2 * radius) / M_PI;
 
    int yCenterOffset = (int)(asinh(tan(centerLat)) * rad2Pixel);
    int yTop = height / 2 - 2 * radius + yCenterOffset;
    int yBottom = yTop + 4 * radius;
 
    return !(yTop >= 0 || yBottom < height);
}