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  1. Qt Mobility
  2. QTMOBILITY-1977

Custom Tile Map Plugins can not override map projection by reimplementing coordinateToWorldReferencePosition()

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Not Evaluated
    • Resolution: Done
    • Affects Version/s: 1.0.0, 1.0.1, 1.0.2, 1.1.0, 1.1.1, 1.1.2
    • Fix Version/s: 1.2.x
    • Component/s: Location
    • Labels:
      None
    • Commits:
      2d388217c0d1c3891aa1fba39f3ccc028f09cd3a

      Description

      The bug is that QGeoTiledMapData::coordinateToScreenPosition uses wrong map projection algorithm.

      It should use the customizable algorithm function:
      QPoint QGeoTiledMapData::coordinateToWorldReferencePosition(const QGeoCoordinate &coordinate) const

      Instead it uses always the default Mercator Spherical algorithm provided in:
      QPoint QGeoTiledMapDataPrivate::coordinateToWorldReferencePosition(double lng, double lat) const

      Here's the default implementation of:
      QPointF QGeoTiledMapData::coordinateToScreenPosition(const QGeoCoordinate &coordwgs) const

      180 QPointF QGeoTiledMapData::coordinateToScreenPosition(const QGeoCoordinate &coordwgs) const
      181 {
      182     Q_D(const QGeoTiledMapData);
      183     return d->coordinateToScreenPosition(coordwgs.longitude(), coordwgs.latitude());
      184 }
      

      As can be seen this directly just calls the private implementation in QGeoTiledMapDataPrivate::coordinateToScreenPosition():

      159 QPointF QGeoTiledMapDataPrivate::coordinateToScreenPosition(double lon, double lat) const
      160 {
      161     QPointF offset = windowOffset();
      162 
      163     QPoint pos(coordinateToWorldReferencePosition(lon, lat));
      164 
      165     const int x = pos.x() - worldReferenceViewportRect.left();
      166 //    if (x < 0)
      167 //        x += worldReferenceSize.width();
      168 
      169     const int y = pos.y() - worldReferenceViewportRect.top();
      170 
      171     QPointF posF(offset.x() + qreal(x) / zoomFactor, offset.y() + qreal(y) / zoomFactor);
      172 
      173     return posF;
      174 }
      

      The map projection is implemented in QGeoTiledMapDataPrivate::coordinateToWorldReferencePosition(), which is a private implementation that can not be customized:

      220 QPoint QGeoTiledMapDataPrivate::coordinateToWorldReferencePosition(double lng, double lat) const
      221 {
      222     lng = lng / 360.0 + 0.5;
      223 
      224     lat = 0.5 - (log(tan((PI / 4.0) + (PI / 2.0) * lat / 180.0)) / PI) / 2.0;
      225     lat = qMax(0.0, lat);
      226     lat = qMin(1.0, lat);
      227 
      228     const double x = lng * worldReferenceSize.width();
      229     const double y = lat * worldReferenceSize.height();
      230 
      231     const QPoint r(int(x > 0 ? x + 0.5 : x - 0.5),
      232                    int(y > 0 ? y + 0.5 : y - 0.5));
      233     return r;
      234 }
      

      As you can see, the implementation never calls the customizable function:
      QPoint QGeoTiledMapData::coordinateToWorldReferencePosition(const QGeoCoordinate &coordinate) const

      Easy workaround candidate is to override the function coordinateToScreenPosition() in custom tile map plugin:
      QPointF QGeoTiledMapData::coordinateToScreenPosition(const QGeoCoordinate &coordwgs) const

      However this does not help since the default tile map plugin implementation uses the wrong coordinateToScreenPosition() function that can not be overridden by custom map plugin implementers (since it is in the private implementation):
      QPointF QGeoMapDataPrivate::coordinateToScreenPosition(double lon, double lat) const

      This private function is directly used e.g. from the QGeoMapObjectEngine class so fixing of this bug into Qt Mobility is very important.
      Otherwise no 3rd party developer can utilize different map projections by customizing the tiled map base implementation!

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            Assignee:
            cadam Cristian Adam
            Reporter:
            kung foo Kung Foo
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              Dates

              Created:
              Updated:
              Resolved:

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