bool SphericalProjection::screenCoordinates( const GeoDataCoordinates &coordinates,
                                             const ViewportParams *viewport,
                                             qreal &x, qreal &y, bool &globeHidesPoint ) const
{
    qDebug() << "SphericalProjection::screenCoordinates() lat: " << coordinates.latitude() << " lon: " << coordinates.longitude() << " type: " << coordinates.getType();
    qreal       absoluteAltitude = coordinates.altitude() + EARTH_RADIUS;
    Quaternion  qpos             = coordinates.quaternion();

    //if (coordinates.getType())
    //    viewport->setClock(coordinates.getClock());
    qpos.rotateAroundAxis( *( viewport->planetAxisMatrix(coordinates.getType() ) ));

    qreal      pixelAltitude = ( ( viewport->radius() )
                                  / EARTH_RADIUS * absoluteAltitude );
    if ( coordinates.altitude() < 10000 ) {
        // Skip placemarks at the other side of the earth.
        if ( qpos.v[Q_Z] < 0 ) {
            globeHidesPoint = true;
            return false;
        }
    }
    else {
        qreal  earthCenteredX = pixelAltitude * qpos.v[Q_X];
        qreal  earthCenteredY = pixelAltitude * qpos.v[Q_Y];
        qreal  radius         = viewport->radius();

        // Don't draw high placemarks (e.g. satellites) that aren't visible.
        if ( qpos.v[Q_Z] < 0
             && ( ( earthCenteredX * earthCenteredX
                    + earthCenteredY * earthCenteredY )
                  < radius * radius ) ) {
            globeHidesPoint = true;
            return false;
        }
    }

    // Let (x, y) be the position on the screen of the placemark..
    x = ((qreal)(viewport->width())  / 2 + pixelAltitude * qpos.v[Q_X]);
    y = ((qreal)(viewport->height()) / 2 - pixelAltitude * qpos.v[Q_Y]);

    // Skip placemarks that are outside the screen area
    if ( x < 0 || x >= viewport->width() || y < 0 || y >= viewport->height() ) {
        globeHidesPoint = false;
        return false;
    }

    globeHidesPoint = false;
    return true;
}