AzimuthalProjection.cpp

// SPDX-License-Identifier: LGPL-2.1-or-later
//
// SPDX-FileCopyrightText: 2014 Gábor Péterffy <peterffy95@gmail.org>
//
 
// Local
#include "AzimuthalProjection.h"
#include "AzimuthalProjection_p.h"
#include "AbstractProjection_p.h"
 
// Marble
#include "GeoDataLinearRing.h"
#include "GeoDataLineString.h"
#include "GeoDataCoordinates.h"
#include "GeoDataLatLonAltBox.h"
#include "ViewportParams.h"
 
#include <QPainterPath>
 
 
namespace Marble {
 
bool AzimuthalProjection::isClippedToSphere() const
{
    return true;
}
 
qreal AzimuthalProjection::clippingRadius() const
{
    return 1;
}
 
bool AzimuthalProjection::screenCoordinates( const GeoDataLineString &lineString,
                                                  const ViewportParams *viewport,
                                                  QVector<QPolygonF *> &polygons ) const
{
 
    Q_D( const AzimuthalProjection );
    // Compare bounding box size of the line string with the angularResolution
    // Immediately return if the latLonAltBox is smaller.
    if ( !viewport->resolves( lineString.latLonAltBox() ) ) {
//      mDebug() << "Object too small to be resolved";
        return false;
    }
 
    d->lineStringToPolygon( lineString, viewport, polygons );
    return true;
}
 
bool AzimuthalProjection::mapCoversViewport( const ViewportParams *viewport ) const
{
        qint64  radius = viewport->radius() * viewport->currentProjection()->clippingRadius();
        qint64  width  = viewport->width();
        qint64  height = viewport->height();
 
        // This first test is a quick one that will catch all really big
        // radii and prevent overflow in the real test.
        if ( radius > width + height )
            return true;
 
        // This is the real test.  The 4 is because we are really
        // comparing to width/2 and height/2.
        if ( 4 * radius * radius >= width * width + height * height )
            return true;
 
        return false;
}
 
GeoDataLatLonAltBox AzimuthalProjection::latLonAltBox( const QRect& screenRect,
                                                       const ViewportParams *viewport ) const
{
    // For the case where the whole viewport gets covered there is a
    // pretty dirty and generic detection algorithm:
    GeoDataLatLonAltBox latLonAltBox = AbstractProjection::latLonAltBox( screenRect, viewport );
 
    // If the whole globe is visible we can easily calculate
    // analytically the lon-/lat- range.
    qreal pitch = GeoDataCoordinates::normalizeLat( viewport->planetAxis().pitch() );
 
    if ( 2.0 * viewport->radius() <= viewport->height()
         &&  2.0 * viewport->radius() <= viewport->width() )
    {
        // Unless the planetaxis is in the screen plane the allowed longitude range
        // covers full -180 deg to +180 deg:
        if ( pitch > 0.0 && pitch < +M_PI ) {
            latLonAltBox.setWest(  -M_PI );
            latLonAltBox.setEast(  +M_PI );
            latLonAltBox.setNorth( +fabs( M_PI / 2.0 - fabs( pitch ) ) );
            latLonAltBox.setSouth( -M_PI / 2.0 );
        }
        if ( pitch < 0.0 && pitch > -M_PI ) {
            latLonAltBox.setWest(  -M_PI );
            latLonAltBox.setEast(  +M_PI );
            latLonAltBox.setNorth( +M_PI / 2.0 );
            latLonAltBox.setSouth( -fabs( M_PI / 2.0 - fabs( pitch ) ) );
        }
 
        // Last but not least we deal with the rare case where the
        // globe is fully visible and pitch = 0.0 or pitch = -M_PI or
        // pitch = +M_PI
        if ( pitch == 0.0 || pitch == -M_PI || pitch == +M_PI ) {
            qreal yaw = viewport->planetAxis().yaw();
            latLonAltBox.setWest( GeoDataCoordinates::normalizeLon( yaw - M_PI / 2.0 ) );
            latLonAltBox.setEast( GeoDataCoordinates::normalizeLon( yaw + M_PI / 2.0 ) );
            latLonAltBox.setNorth( +M_PI / 2.0 );
            latLonAltBox.setSouth( -M_PI / 2.0 );
        }
 
        return latLonAltBox;
    }
 
    // Now we check whether maxLat (e.g. the north pole) gets displayed
    // inside the viewport to get more accurate values for east and west.
 
    // We need a point on the screen at maxLat that definitely gets displayed:
    qreal averageLongitude = ( latLonAltBox.west() + latLonAltBox.east() ) / 2.0;
 
    GeoDataCoordinates maxLatPoint( averageLongitude, maxLat(), 0.0, GeoDataCoordinates::Radian );
    GeoDataCoordinates minLatPoint( averageLongitude, minLat(), 0.0, GeoDataCoordinates::Radian );
 
    qreal dummyX, dummyY; // not needed
    bool dummyVal;
 
    if ( screenCoordinates( maxLatPoint, viewport, dummyX, dummyY, dummyVal ) ||
         screenCoordinates( minLatPoint, viewport, dummyX, dummyY, dummyVal ) ) {
        latLonAltBox.setWest( -M_PI );
        latLonAltBox.setEast( +M_PI );
    }
 
    return latLonAltBox;
}
 
QPainterPath AzimuthalProjection::mapShape( const ViewportParams *viewport ) const
{
    int  radius    = viewport->radius() * viewport->currentProjection()->clippingRadius();
    int  imgWidth  = viewport->width();
    int  imgHeight = viewport->height();
 
    QPainterPath fullRect;
    fullRect.addRect(  0 , 0 , imgWidth, imgHeight );
 
    // If the globe covers the whole image, then the projected region represents
    // all of the image.
    // Otherwise the active region has got the shape of the visible globe.
 
    if ( !viewport->mapCoversViewport() ) {
        QPainterPath mapShape;
        mapShape.addEllipse(
            imgWidth  / 2 - radius,
            imgHeight / 2 - radius,
            2 * radius,
            2 * radius );
        return mapShape.intersected( fullRect );
    }
 
    return fullRect;
}
 
AzimuthalProjection::AzimuthalProjection(AzimuthalProjectionPrivate * dd) :
    AbstractProjection( dd )
{
}
 
AzimuthalProjection::~AzimuthalProjection()
{
}
 
void AzimuthalProjectionPrivate::tessellateLineSegment( const GeoDataCoordinates &aCoords,
                                                qreal ax, qreal ay,
                                                const GeoDataCoordinates &bCoords,
                                                qreal bx, qreal by,
                                                QVector<QPolygonF*> &polygons,
                                                const ViewportParams *viewport,
                                                TessellationFlags f,
                                                bool allowLatePolygonCut ) const
{
    // We take the manhattan length as a distance approximation
    // that can be too big by a factor of sqrt(2)
    qreal distance = fabs((bx - ax)) + fabs((by - ay));
#ifdef SAFE_DISTANCE
    // Interpolate additional nodes if the line segment that connects the
    // current or previous nodes might cross the viewport.
    // The latter can pretty safely be excluded for most projections if both points
    // are located on the same side relative to the viewport boundaries and if they are
    // located more than half the line segment distance away from the viewport.
    const qreal safeDistance = - 0.5 * distance;
    if (   !( bx < safeDistance && ax < safeDistance )
        || !( by < safeDistance && ay < safeDistance )
        || !( bx + safeDistance > viewport->width()
            && ax + safeDistance > viewport->width() )
        || !( by + safeDistance > viewport->height()
            && ay + safeDistance > viewport->height() )
    )
    {
#endif
        int maxTessellationFactor = viewport->radius() < 20000 ? 10 : 20;
        int const finalTessellationPrecision = qBound(2, viewport->radius()/200, maxTessellationFactor) * tessellationPrecision;
 
        // Let the line segment follow the spherical surface
        // if the distance between the previous point and the current point
        // on screen is too big
 
        if ( distance > finalTessellationPrecision ) {
            const int tessellatedNodes = qMin<int>( distance / finalTessellationPrecision, maxTessellationNodes );
 
            processTessellation( aCoords, bCoords,
                                 tessellatedNodes,
                                 polygons,
                                 viewport,
                                 f,
                                 allowLatePolygonCut);
        }
        else {
            crossHorizon( bCoords, polygons, viewport, allowLatePolygonCut );
        }
#ifdef SAFE_DISTANCE
    }
#endif
}
 
 
void AzimuthalProjectionPrivate::processTessellation( const GeoDataCoordinates &previousCoords,
                                                    const GeoDataCoordinates &currentCoords,
                                                    int tessellatedNodes,
                                                    QVector<QPolygonF*> &polygons,
                                                    const ViewportParams *viewport,
                                                    TessellationFlags f,
                                                    bool allowLatePolygonCut ) const
{
 
    const bool clampToGround = f.testFlag( FollowGround );
    const bool followLatitudeCircle = f.testFlag( RespectLatitudeCircle )
                                      && previousCoords.latitude() == currentCoords.latitude();
 
    // Calculate steps for tessellation: lonDiff and altDiff
    qreal lonDiff = 0.0;
    if ( followLatitudeCircle ) {
        const int previousSign = previousCoords.longitude() > 0 ? 1 : -1;
        const int currentSign = currentCoords.longitude() > 0 ? 1 : -1;
 
        lonDiff = currentCoords.longitude() - previousCoords.longitude();
        if ( previousSign != currentSign
             && fabs(previousCoords.longitude()) + fabs(currentCoords.longitude()) > M_PI ) {
            if ( previousSign > currentSign ) {
                // going eastwards ->
                lonDiff += 2 * M_PI ;
            } else {
                // going westwards ->
                lonDiff -= 2 * M_PI;
            }
        }
    }
 
    // Create the tessellation nodes.
    GeoDataCoordinates previousTessellatedCoords = previousCoords;
    for ( int i = 1; i <= tessellatedNodes; ++i ) {
        const qreal t = (qreal)(i) / (qreal)( tessellatedNodes + 1 );
 
        GeoDataCoordinates currentTessellatedCoords;
 
        if ( followLatitudeCircle ) {
            // To tessellate along latitude circles use the
            // linear interpolation of the longitude.
            const qreal altDiff = currentCoords.altitude() - previousCoords.altitude();
            const qreal altitude = altDiff * t + previousCoords.altitude();
            const qreal lon = lonDiff * t + previousCoords.longitude();
            const qreal lat = previousTessellatedCoords.latitude();
 
            currentTessellatedCoords = GeoDataCoordinates(lon, lat, altitude);
        }
        else {
            // To tessellate along great circles use the
            // normalized linear interpolation ("NLERP") for latitude and longitude.
            currentTessellatedCoords = previousCoords.nlerp(currentCoords, t);
        }
 
        if (clampToGround) {
            currentTessellatedCoords.setAltitude(0);
        }
 
        crossHorizon( currentTessellatedCoords, polygons, viewport, allowLatePolygonCut );
        previousTessellatedCoords = currentTessellatedCoords;
    }
 
    // For the clampToGround case add the "current" coordinate after adding all other nodes.
    GeoDataCoordinates currentModifiedCoords( currentCoords );
    if ( clampToGround ) {
        currentModifiedCoords.setAltitude( 0.0 );
    }
    crossHorizon( currentModifiedCoords, polygons, viewport, allowLatePolygonCut );
}
 
void AzimuthalProjectionPrivate::crossHorizon( const GeoDataCoordinates & bCoord,
                                              QVector<QPolygonF*> &polygons,
                                              const ViewportParams *viewport,
                                              bool allowLatePolygonCut
                                             ) const
{
    qreal x, y;
    bool globeHidesPoint;
 
    Q_Q( const AbstractProjection );
 
    q->screenCoordinates( bCoord, viewport, x, y, globeHidesPoint );
 
    if( !globeHidesPoint ) {
        *polygons.last() << QPointF( x, y );
    }
    else {
        if ( allowLatePolygonCut && !polygons.last()->isEmpty() ) {
            QPolygonF *path = new QPolygonF;
            polygons.append( path );
        }
    }
}
 
bool AzimuthalProjectionPrivate::lineStringToPolygon( const GeoDataLineString &lineString,
                                              const ViewportParams *viewport,
                                              QVector<QPolygonF *> &polygons ) const
{
    Q_Q( const AzimuthalProjection );
 
    const TessellationFlags f = lineString.tessellationFlags();
    bool const tessellate = lineString.tessellate();
    const bool noFilter = f.testFlag(PreventNodeFiltering);
 
 
    qreal x = 0;
    qreal y = 0;
    bool globeHidesPoint = false;
 
    qreal previousX = -1.0;
    qreal previousY = -1.0;
    bool previousGlobeHidesPoint = false;
 
    qreal horizonX = -1.0;
    qreal horizonY = -1.0;
 
    QPolygonF * polygon = new QPolygonF;
    if (!tessellate) {
        polygon->reserve(lineString.size());
    }
    polygons.append( polygon );
 
    GeoDataLineString::ConstIterator itCoords = lineString.constBegin();
    GeoDataLineString::ConstIterator itPreviousCoords = lineString.constBegin();
 
    // Some projections display the earth in a way so that there is a
    // foreside and a backside.
    // The horizon is the line (usually a circle) which separates both
    // sides from each other and resembles the map shape.
    GeoDataCoordinates horizonCoords;
 
    // A horizon pair is a pair of two subsequent horizon crossings:
    // The first one describes the point where a line string disappears behind the horizon.
    // and where horizonPair is set to true.
    // The second one describes the point where the line string reappears.
    // In this case the two points are connected and horizonPair is set to false again.
    bool horizonPair = false;
    GeoDataCoordinates horizonDisappearCoords;
 
    // If the first horizon crossing in a line string describes the appearance of
    // a line string then we call it a "horizon orphan" and horizonOrphan is set to true.
    // In this case once the last horizon crossing in the line string is reached
    // it needs to be connected to the orphan.
    bool horizonOrphan = false;
    GeoDataCoordinates horizonOrphanCoords;
 
    GeoDataLineString::ConstIterator itBegin = lineString.constBegin();
    GeoDataLineString::ConstIterator itEnd = lineString.constEnd();
 
    bool processingLastNode = false;
 
    // We use a while loop to be able to cover linestrings as well as linear rings:
    // Linear rings require to tessellate the path from the last node to the first node
    // which isn't really convenient to achieve with a for loop ...
 
    const bool isLong = lineString.size() > 10;
    const int maximumDetail = levelForResolution(viewport->angularResolution());
    // The first node of optimized linestrings has a non-zero detail value.
    const bool hasDetail = itBegin->detail() != 0;
 
    while ( itCoords != itEnd )
    {
        // Optimization for line strings with a big amount of nodes
        bool skipNode = (hasDetail ? itCoords->detail() > maximumDetail
                : itCoords != itBegin && isLong && !processingLastNode &&
                !viewport->resolves( *itPreviousCoords, *itCoords ) );
 
        if ( !skipNode || noFilter) {
 
            q->screenCoordinates( *itCoords, viewport, x, y, globeHidesPoint );
 
            // Initializing variables that store the values of the previous iteration
            if ( !processingLastNode && itCoords == itBegin ) {
                previousGlobeHidesPoint = globeHidesPoint;
                itPreviousCoords = itCoords;
                previousX = x;
                previousY = y;
            }
 
            // Check for the "horizon case" (which is present e.g. for the spherical projection
            const bool isAtHorizon = ( globeHidesPoint || previousGlobeHidesPoint ) &&
                                     ( globeHidesPoint !=  previousGlobeHidesPoint );
 
            if ( isAtHorizon ) {
                // Handle the "horizon case"
                horizonCoords = findHorizon( *itPreviousCoords, *itCoords, viewport, f );
 
                if ( lineString.isClosed() ) {
                    if ( horizonPair ) {
                        horizonToPolygon( viewport, horizonDisappearCoords, horizonCoords, polygons.last() );
                        horizonPair = false;
                    }
                    else {
                        if ( globeHidesPoint ) {
                            horizonDisappearCoords = horizonCoords;
                            horizonPair = true;
                        }
                        else {
                            horizonOrphanCoords = horizonCoords;
                            horizonOrphan = true;
                        }
                    }
                }
 
                q->screenCoordinates( horizonCoords, viewport, horizonX, horizonY );
 
                // If the line appears on the visible half we need
                // to add an interpolated point at the horizon as the previous point.
                if ( previousGlobeHidesPoint ) {
                    *polygons.last() << QPointF( horizonX, horizonY );
                }
            }
 
            // This if-clause contains the section that tessellates the line
            // segments of a linestring. If you are about to learn how the code of
            // this class works you can safely ignore this section for a start.
 
            if ( lineString.tessellate() /* && ( isVisible || previousIsVisible ) */ ) {
 
                if ( !isAtHorizon ) {
 
                    tessellateLineSegment( *itPreviousCoords, previousX, previousY,
                                           *itCoords, x, y,
                                           polygons, viewport,
                                           f, !lineString.isClosed() );
 
                }
                else {
                    // Connect the interpolated  point at the horizon with the
                    // current or previous point in the line.
                    if ( previousGlobeHidesPoint ) {
                        tessellateLineSegment( horizonCoords, horizonX, horizonY,
                                               *itCoords, x, y,
                                               polygons, viewport,
                                               f, !lineString.isClosed() );
                    }
                    else {
                        tessellateLineSegment( *itPreviousCoords, previousX, previousY,
                                               horizonCoords, horizonX, horizonY,
                                               polygons, viewport,
                                               f, !lineString.isClosed() );
                    }
                }
            }
            else {
                if ( !globeHidesPoint ) {
                    *polygons.last() << QPointF( x, y );
                }
                else {
                    if ( !previousGlobeHidesPoint && isAtHorizon ) {
                        *polygons.last() << QPointF( horizonX, horizonY );
                    }
                }
            }
 
            if ( globeHidesPoint ) {
                if (   !previousGlobeHidesPoint
                    && !lineString.isClosed()
                    ) {
                    polygons.append( new QPolygonF );
                }
            }
 
            previousGlobeHidesPoint = globeHidesPoint;
            itPreviousCoords = itCoords;
            previousX = x;
            previousY = y;
        }
 
        // Here we modify the condition to be able to process the
        // first node after the last node in a LinearRing.
 
        if ( processingLastNode ) {
            break;
        }
        ++itCoords;
 
        if ( itCoords == itEnd  && lineString.isClosed() ) {
            itCoords = itBegin;
            processingLastNode = true;
        }
    }
 
    // In case of horizon crossings, make sure that we always get a
    // polygon closed correctly.
    if ( horizonOrphan && lineString.isClosed() ) {
        horizonToPolygon( viewport, horizonCoords, horizonOrphanCoords, polygons.last() );
    }
 
    if ( polygons.last()->size() <= 1 ){
        delete polygons.last();
        polygons.pop_back(); // Clean up "unused" empty polygon instances
    }
 
    return polygons.isEmpty();
}
 
void AzimuthalProjectionPrivate::horizonToPolygon( const ViewportParams *viewport,
                                           const GeoDataCoordinates & disappearCoords,
                                           const GeoDataCoordinates & reappearCoords,
                                           QPolygonF * polygon ) const
{
    qreal x, y;
 
    const qreal imageHalfWidth  = viewport->width() / 2;
    const qreal imageHalfHeight = viewport->height() / 2;
 
    bool dummyGlobeHidesPoint = false;
 
    Q_Q( const AzimuthalProjection );
    // Calculate the angle of the position vectors of both coordinates
    q->screenCoordinates( disappearCoords, viewport, x, y, dummyGlobeHidesPoint );
    qreal alpha = atan2( y - imageHalfHeight,
                         x - imageHalfWidth );
 
    q->screenCoordinates( reappearCoords, viewport, x, y, dummyGlobeHidesPoint );
    qreal beta =  atan2( y - imageHalfHeight,
                         x - imageHalfWidth );
 
    // Calculate the difference between both
    qreal diff = GeoDataCoordinates::normalizeLon( beta - alpha );
 
    qreal sgndiff = diff < 0 ? -1 : 1;
 
    const qreal arcradius = q->clippingRadius() * viewport->radius();
    const int itEnd = fabs(diff * RAD2DEG);
 
    // Create a polygon that resembles an arc between the two position vectors
    polygon->reserve(polygon->size() + itEnd);
    for ( int it = 1; it <= itEnd; ++it ) {
        const qreal angle = alpha + DEG2RAD * sgndiff * it;
        const qreal itx = imageHalfWidth  +  arcradius * cos( angle );
        const qreal ity = imageHalfHeight +  arcradius * sin( angle );
        *polygon << QPointF( itx, ity );
    }
}
 
 
GeoDataCoordinates AzimuthalProjectionPrivate::findHorizon( const GeoDataCoordinates & previousCoords,
                                                    const GeoDataCoordinates & currentCoords,
                                                    const ViewportParams *viewport,
                                                    TessellationFlags f) const
{
    bool currentHide = globeHidesPoint( currentCoords, viewport ) ;
 
    return doFindHorizon(previousCoords, currentCoords, viewport, f, currentHide, 0);
}
 
 
GeoDataCoordinates AzimuthalProjectionPrivate::doFindHorizon( const GeoDataCoordinates & previousCoords,
                                                    const GeoDataCoordinates & currentCoords,
                                                    const ViewportParams *viewport,
                                                    TessellationFlags f,
                                                    bool currentHide,
                                                    int recursionCounter ) const
{
    if ( recursionCounter > 20 ) {
        return currentHide ? previousCoords : currentCoords;
    }
    ++recursionCounter;
 
    bool followLatitudeCircle = false;
 
    // Calculate steps for tessellation: lonDiff and altDiff
    qreal lonDiff = 0.0;
    qreal previousLongitude = 0.0;
    qreal previousLatitude = 0.0;
 
    if ( f.testFlag( RespectLatitudeCircle ) ) {
        previousCoords.geoCoordinates( previousLongitude, previousLatitude );
        qreal previousSign = previousLongitude > 0 ? 1 : -1;
 
        qreal currentLongitude = 0.0;
        qreal currentLatitude = 0.0;
        currentCoords.geoCoordinates( currentLongitude, currentLatitude );
        qreal currentSign = currentLongitude > 0 ? 1 : -1;
 
        if ( previousLatitude == currentLatitude ) {
            followLatitudeCircle = true;
 
            lonDiff = currentLongitude - previousLongitude;
            if ( previousSign != currentSign
                 && fabs(previousLongitude) + fabs(currentLongitude) > M_PI ) {
                if ( previousSign > currentSign ) {
                    // going eastwards ->
                    lonDiff += 2 * M_PI ;
                } else {
                    // going westwards ->
                    lonDiff -= 2 * M_PI;
                }
            }
 
        }
        else {
//            mDebug() << "Don't FollowLatitudeCircle";
        }
    }
 
    GeoDataCoordinates horizonCoords;
 
    if ( followLatitudeCircle ) {
        // To tessellate along latitude circles use the
        // linear interpolation of the longitude.
        const qreal altDiff = currentCoords.altitude() - previousCoords.altitude();
        const qreal altitude = previousCoords.altitude() + 0.5 * altDiff;
        const qreal lon = lonDiff * 0.5 + previousLongitude;
        const qreal lat = previousLatitude;
 
        horizonCoords = GeoDataCoordinates(lon, lat, altitude);
    }
    else {
        // To tessellate along great circles use the
        // normalized linear interpolation ("NLERP") for latitude and longitude.
        horizonCoords = previousCoords.nlerp(currentCoords, 0.5);
    }
 
    bool horizonHide = globeHidesPoint( horizonCoords, viewport );
 
    if ( horizonHide != currentHide ) {
        return doFindHorizon(horizonCoords, currentCoords, viewport, f, currentHide, recursionCounter);
    }
 
    return doFindHorizon(previousCoords, horizonCoords, viewport, f, horizonHide, recursionCounter);
}
 
 
bool AzimuthalProjectionPrivate::globeHidesPoint( const GeoDataCoordinates &coordinates,
                                          const ViewportParams *viewport ) const
{
    bool globeHidesPoint;
    qreal dummyX, dummyY;
 
    Q_Q( const AzimuthalProjection );
    q->screenCoordinates(coordinates, viewport, dummyX, dummyY, globeHidesPoint);
    return globeHidesPoint;
}
 
 
}