C++ (Cpp) QgsDistanceArea::lengthUnits示例

double QgsLayoutItemScaleBar::mapWidth() const
{
  if ( !mMap )
  {
    return 0.0;
  }

  QgsRectangle mapExtent = mMap->extent();
  if ( mSettings.units() == QgsUnitTypes::DistanceUnknownUnit )
  {
    return mapExtent.width();
  }
  else
  {
    QgsDistanceArea da;
    da.setSourceCrs( mMap->crs(), mLayout->project()->transformContext() );
    da.setEllipsoid( mLayout->project()->ellipsoid() );

    QgsUnitTypes::DistanceUnit units = da.lengthUnits();
    double measure = da.measureLine( QgsPointXY( mapExtent.xMinimum(), mapExtent.yMinimum() ),
                                     QgsPointXY( mapExtent.xMaximum(), mapExtent.yMinimum() ) );
    measure /= QgsUnitTypes::fromUnitToUnitFactor( mSettings.units(), units );
    return measure;
  }
}