[composer] Allow syncing pictures to true north

Previously pictures could only be synced to grid north, which
can be totally wrong for many CRSes (especially in polar areas)

Users now are given a choice of grid or true north, and can also
enter an optional offset to apply if eg magnetic north is instead
desired.

When synced to true north the bearing is calculated using the
centre point of the linked map item.

Fix #192, #4711

This fix was sponsored by the Norwegian Polar Institute's
Quantarctica project (http://quantarctica.npolar.no) and
coordinated by Faunalia.

(cherry-picked from 89cc645)

python/core/composer/qgscomposerpicture.sip

@@ -30,6 +30,13 @@ class QgsComposerPicture: QgsComposerItem
       Unknown
     };
 
+    //! Method for syncing rotation to a map's North direction
+    enum NorthMode
+    {
+      GridNorth, /*!< Align to grid north */
+      TrueNorth, /*!< Align to true north */
+    };
+
     QgsComposerPicture( QgsComposition *composition /TransferThis/);
     ~QgsComposerPicture();
 
@@ -132,6 +139,38 @@ class QgsComposerPicture: QgsComposerItem
      */
     bool useRotationMap() const;
 
+     /**
+     * Returns the mode used to align the picture to a map's North.
+     * @see setNorthMode()
+     * @see northOffset()
+     * @note added in QGIS 2.18
+     */
+    NorthMode northMode() const;
+
+    /**
+     * Sets the mode used to align the picture to a map's North.
+     * @see northMode()
+     * @see setNorthOffset()
+     * @note added in QGIS 2.18
+     */
+    void setNorthMode( NorthMode mode );
+
+    /**
+     * Returns the offset added to the picture's rotation from a map's North.
+     * @see setNorthOffset()
+     * @see northMode()
+     * @note added in QGIS 2.18
+     */
+    double northOffset() const;
+
+    /**
+     * Sets the offset added to the picture's rotation from a map's North.
+     * @see northOffset()
+     * @see setNorthMode()
+     * @note added in QGIS 2.18
+     */
+    void setNorthOffset( double offset );
+
     /** Returns the resize mode used for drawing the picture within the composer
      * item's frame.
      * @returns resize mode of picture

python/core/core.sip

@@ -21,6 +21,7 @@
 %Include qgsannotation.sip
 %Include qgsapplication.sip
 %Include qgsattributeaction.sip
+%Include qgsbearingutils.sip
 %Include qgsbrowsermodel.sip
 %Include qgsclipper.sip
 %Include qgscolorscheme.sip

python/core/qgsbearingutils.sip

@@ -0,0 +1,21 @@
+/**
+ * \class QgsBearingUtils
+ * \ingroup core
+ * Utilities for calculating bearings and directions.
+ * \note Added in version 2.18
+*/
+class QgsBearingUtils
+{
+%TypeHeaderCode
+#include <qgsbearingutils.h>
+%End
+  public:
+
+    /**
+     * Returns the direction to true north from a specified point and for a specified
+     * coordinate reference system. The returned value is in degrees clockwise from
+     * vertical. An exception will be thrown if the bearing could not be calculated.
+     */
+    static double bearingTrueNorth( const QgsCoordinateReferenceSystem& crs,
+                                    const QgsPoint& point );
+};

src/app/composer/qgscomposerpicturewidget.cpp

@@ -44,6 +44,13 @@ QgsComposerPictureWidget::QgsComposerPictureWidget( QgsComposerPicture* picture
   mOutlineColorButton->setColorDialogTitle( tr( "Select outline color" ) );
   mOutlineColorButton->setContext( "composer" );
 
+  mNorthTypeComboBox->blockSignals( true );
+  mNorthTypeComboBox->addItem( tr( "Grid north" ), QgsComposerPicture::GridNorth );
+  mNorthTypeComboBox->addItem( tr( "True north" ), QgsComposerPicture::TrueNorth );
+  mNorthTypeComboBox->blockSignals( false );
+  mPictureRotationOffsetSpinBox->setClearValue( 0.0 );
+  mPictureRotationSpinBox->setClearValue( 0.0 );
+
   //add widget for general composer item properties
   QgsComposerItemWidget* itemPropertiesWidget = new QgsComposerItemWidget( this, picture );
   mainLayout->addWidget( itemPropertiesWidget );
@@ -273,6 +280,8 @@ void QgsComposerPictureWidget::on_mRotationFromComposerMapCheckBox_stateChanged(
     mPicture->setRotationMap( -1 );
     mPictureRotationSpinBox->setEnabled( true );
     mComposerMapComboBox->setEnabled( false );
+    mNorthTypeComboBox->setEnabled( false );
+    mPictureRotationOffsetSpinBox->setEnabled( false );
     mPicture->setPictureRotation( mPictureRotationSpinBox->value() );
   }
   else
@@ -286,6 +295,8 @@ void QgsComposerPictureWidget::on_mRotationFromComposerMapCheckBox_stateChanged(
 
     mPicture->setRotationMap( composerId );
     mPictureRotationSpinBox->setEnabled( false );
+    mNorthTypeComboBox->setEnabled( true );
+    mPictureRotationOffsetSpinBox->setEnabled( true );
     mComposerMapComboBox->setEnabled( true );
   }
   mPicture->endCommand();
@@ -388,6 +399,8 @@ void QgsComposerPictureWidget::setGuiElementValues()
     mPictureLineEdit->blockSignals( true );
     mComposerMapComboBox->blockSignals( true );
     mRotationFromComposerMapCheckBox->blockSignals( true );
+    mNorthTypeComboBox->blockSignals( true );
+    mPictureRotationOffsetSpinBox->blockSignals( true );
     mResizeModeComboBox->blockSignals( true );
     mAnchorPointComboBox->blockSignals( true );
     mFillColorButton->blockSignals( true );
@@ -410,13 +423,19 @@ void QgsComposerPictureWidget::setGuiElementValues()
       {
         mComposerMapComboBox->setCurrentIndex( itemId );
       }
+      mNorthTypeComboBox->setEnabled( true );
+      mPictureRotationOffsetSpinBox->setEnabled( true );
     }
     else
     {
       mRotationFromComposerMapCheckBox->setCheckState( Qt::Unchecked );
       mPictureRotationSpinBox->setEnabled( true );
       mComposerMapComboBox->setEnabled( false );
+      mNorthTypeComboBox->setEnabled( false );
+      mPictureRotationOffsetSpinBox->setEnabled( false );
     }
+    mNorthTypeComboBox->setCurrentIndex( mNorthTypeComboBox->findData( mPicture->northMode() ) );
+    mPictureRotationOffsetSpinBox->setValue( mPicture->northOffset() );
 
     mResizeModeComboBox->setCurrentIndex(( int )mPicture->resizeMode() );
     //disable picture rotation for non-zoom modes
@@ -444,6 +463,8 @@ void QgsComposerPictureWidget::setGuiElementValues()
     mPictureRotationSpinBox->blockSignals( false );
     mPictureLineEdit->blockSignals( false );
     mComposerMapComboBox->blockSignals( false );
+    mNorthTypeComboBox->blockSignals( false );
+    mPictureRotationOffsetSpinBox->blockSignals( false );
     mResizeModeComboBox->blockSignals( false );
     mAnchorPointComboBox->blockSignals( false );
     mFillColorButton->blockSignals( false );
@@ -726,6 +747,22 @@ void QgsComposerPictureWidget::showEvent( QShowEvent * event )
   refreshMapComboBox();
 }
 
+void QgsComposerPictureWidget::on_mPictureRotationOffsetSpinBox_valueChanged( double d )
+{
+  mPicture->beginCommand( tr( "Picture North offset changed" ), QgsComposerMergeCommand::ComposerPictureNorthOffset );
+  mPicture->setNorthOffset( d );
+  mPicture->endCommand();
+  mPicture->update();
+}
+
+void QgsComposerPictureWidget::on_mNorthTypeComboBox_currentIndexChanged( int index )
+{
+  mPicture->beginCommand( tr( "Picture North mode changed" ) );
+  mPicture->setNorthMode( static_cast< QgsComposerPicture::NorthMode >( mNorthTypeComboBox->itemData( index ).toInt() ) );
+  mPicture->endCommand();
+  mPicture->update();
+}
+
 void QgsComposerPictureWidget::resizeEvent( QResizeEvent * event )
 {
   Q_UNUSED( event );

src/app/composer/qgscomposerpicturewidget.h

@@ -73,6 +73,8 @@ class QgsComposerPictureWidget: public QgsComposerItemBaseWidget, private Ui::Qg
     void on_mFillColorButton_colorChanged( const QColor& color );
     void on_mOutlineColorButton_colorChanged( const QColor& color );
     void on_mOutlineWidthSpinBox_valueChanged( double d );
+    void on_mPictureRotationOffsetSpinBox_valueChanged( double d );
+    void on_mNorthTypeComboBox_currentIndexChanged( int index );
 
   private:
     QgsComposerPicture* mPicture;

src/core/CMakeLists.txt

@@ -76,6 +76,7 @@ SET(QGIS_CORE_SRCS
   qgis.cpp
   qgsapplication.cpp
   qgsattributeaction.cpp
+  qgsbearingutils.cpp
   qgsbrowsermodel.cpp
   qgscachedfeatureiterator.cpp
   qgscacheindex.cpp
@@ -583,6 +584,7 @@ SET(QGIS_CORE_HDRS
   qgis.h
   qgsannotation.h
   qgsattributeaction.h
+  qgsbearingutils.h
   qgscachedfeatureiterator.h
   qgscacheindex.h
   qgscacheindexfeatureid.h

src/core/composer/qgscomposeritemcommand.h

@@ -105,6 +105,7 @@ class CORE_EXPORT QgsComposerMergeCommand: public QgsComposerItemCommand
       LegendRasterBorderWidth,
       //composer picture
       ComposerPictureRotation,
+      ComposerPictureNorthOffset,
       // composer scalebar
       ScaleBarLineWidth,
       ScaleBarHeight,

src/core/composer/qgscomposerpicture.cpp

@@ -28,6 +28,10 @@
 #include "qgsnetworkcontentfetcher.h"
 #include "qgssymbollayerv2utils.h"
 #include "qgssvgcache.h"
+#include "qgslogger.h"
+#include "qgsbearingutils.h"
+#include "qgsmapsettings.h"
+
 #include <QDomDocument>
 #include <QDomElement>
 #include <QFileInfo>
@@ -44,6 +48,8 @@ QgsComposerPicture::QgsComposerPicture( QgsComposition *composition )
     , mMode( Unknown )
     , mPictureRotation( 0 )
     , mRotationMap( nullptr )
+    , mNorthMode( GridNorth )
+    , mNorthOffset( 0.0 )
     , mResizeMode( QgsComposerPicture::Zoom )
     , mPictureAnchor( UpperLeft )
     , mSvgFillColor( QColor( 255, 255, 255 ) )
@@ -61,6 +67,8 @@ QgsComposerPicture::QgsComposerPicture()
     , mMode( Unknown )
     , mPictureRotation( 0 )
     , mRotationMap( nullptr )
+    , mNorthMode( GridNorth )
+    , mNorthOffset( 0.0 )
     , mResizeMode( QgsComposerPicture::Zoom )
     , mPictureAnchor( UpperLeft )
     , mSvgFillColor( QColor( 255, 255, 255 ) )
@@ -419,6 +427,43 @@ void QgsComposerPicture::remotePictureLoaded()
   mLoaded = true;
 }
 
+void QgsComposerPicture::updateMapRotation()
+{
+  if ( !mRotationMap )
+    return;
+
+  // take map rotation
+  double rotation = mRotationMap->mapRotation();
+
+  // handle true north
+  switch ( mNorthMode )
+  {
+    case GridNorth:
+      break; // nothing to do
+
+    case TrueNorth:
+    {
+      QgsPoint center = mRotationMap->currentMapExtent()->center();
+      QgsCoordinateReferenceSystem crs = mComposition->mapSettings().destinationCrs();
+
+      try
+      {
+        double bearing = QgsBearingUtils::bearingTrueNorth( crs, center );
+        rotation += bearing;
+      }
+      catch ( QgsException& e )
+      {
+        Q_UNUSED( e );
+        QgsDebugMsg( QString( "Caught exception %1" ).arg( e.what() ) );
+      }
+      break;
+    }
+  }
+
+  rotation += mNorthOffset;
+  setPictureRotation( rotation );
+}
+
 void QgsComposerPicture::loadPicture( const QString &path )
 {
   if ( path.startsWith( "http" ) )
@@ -650,7 +695,8 @@ void QgsComposerPicture::setRotationMap( int composerMapId )
 
   if ( composerMapId == -1 ) //disable rotation from map
   {
-    QObject::disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( setPictureRotation( double ) ) );
+    disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( updateMapRotation() ) );
+    disconnect( mRotationMap, SIGNAL( extentChanged() ), this, SLOT( updateMapRotation() ) );
     mRotationMap = nullptr;
   }
 
@@ -661,12 +707,14 @@ void QgsComposerPicture::setRotationMap( int composerMapId )
   }
   if ( mRotationMap )
   {
-    QObject::disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( setPictureRotation( double ) ) );
+    disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( updateMapRotation() ) );
+    disconnect( mRotationMap, SIGNAL( extentChanged() ), this, SLOT( updateMapRotation() ) );
   }
   mPictureRotation = map->mapRotation();
-  QObject::connect( map, SIGNAL( mapRotationChanged( double ) ), this, SLOT( setPictureRotation( double ) ) );
+  connect( map, SIGNAL( mapRotationChanged( double ) ), this, SLOT( updateMapRotation() ) );
+  connect( map, SIGNAL( extentChanged() ), this, SLOT( updateMapRotation() ) );
   mRotationMap = map;
-  update();
+  updateMapRotation();
   emit pictureRotationChanged( mPictureRotation );
 }
 
@@ -761,6 +809,8 @@ bool QgsComposerPicture::writeXML( QDomElement& elem, QDomDocument & doc ) const
   {
     composerPictureElem.setAttribute( "mapId", mRotationMap->id() );
   }
+  composerPictureElem.setAttribute( "northMode", mNorthMode );
+  composerPictureElem.setAttribute( "northOffset", mNorthOffset );
 
   _writeXML( composerPictureElem, doc );
   elem.appendChild( composerPictureElem );
@@ -827,6 +877,9 @@ bool QgsComposerPicture::readXML( const QDomElement& itemElem, const QDomDocumen
   }
 
   //rotation map
+  mNorthMode = static_cast< NorthMode >( itemElem.attribute( "northMode", "0" ).toInt() );
+  mNorthOffset = itemElem.attribute( "northOffset", "0" ).toDouble();
+
   int rotationMapId = itemElem.attribute( "mapId", "-1" ).toInt();
   if ( rotationMapId == -1 )
   {
@@ -837,10 +890,12 @@ bool QgsComposerPicture::readXML( const QDomElement& itemElem, const QDomDocumen
 
     if ( mRotationMap )
     {
-      QObject::disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( setRotation( double ) ) );
+      disconnect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( updateMapRotation() ) );
+      disconnect( mRotationMap, SIGNAL( extentChanged() ), this, SLOT( updateMapRotation() ) );
     }
     mRotationMap = mComposition->getComposerMapById( rotationMapId );
-    QObject::connect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( setRotation( double ) ) );
+    connect( mRotationMap, SIGNAL( mapRotationChanged( double ) ), this, SLOT( updateMapRotation() ) );
+    connect( mRotationMap, SIGNAL( extentChanged() ), this, SLOT( updateMapRotation() ) );
   }
 
   refreshPicture();
@@ -861,6 +916,18 @@ int QgsComposerPicture::rotationMap() const
   }
 }
 
+void QgsComposerPicture::setNorthMode( QgsComposerPicture::NorthMode mode )
+{
+  mNorthMode = mode;
+  updateMapRotation();
+}
+
+void QgsComposerPicture::setNorthOffset( double offset )
+{
+  mNorthOffset = offset;
+  updateMapRotation();
+}
+
 void QgsComposerPicture::setPictureAnchor( QgsComposerItem::ItemPositionMode anchor )
 {
   mPictureAnchor = anchor;