Add scale method option for layout scale bars

python/PyQt6/core/auto_additions/qgis.py

@@ -9662,6 +9662,23 @@
 """
 # --
 Qgis.PictureFormat.baseClass = Qgis
+# monkey patching scoped based enum
+Qgis.ScaleCalculationMethod.HorizontalTop.__doc__ = "Calculate horizontally, across top of map"
+Qgis.ScaleCalculationMethod.HorizontalMiddle.__doc__ = "Calculate horizontally, across midle of map"
+Qgis.ScaleCalculationMethod.HorizontalBottom.__doc__ = "Calculate horizontally, across bottom of map"
+Qgis.ScaleCalculationMethod.HorizontalAverage.__doc__ = "Calculate horizontally, using the average of the top, middle and bottom scales"
+Qgis.ScaleCalculationMethod.__doc__ = """Scale calculation logic.
+
+.. versionadded:: 3.40
+
+* ``HorizontalTop``: Calculate horizontally, across top of map
+* ``HorizontalMiddle``: Calculate horizontally, across midle of map
+* ``HorizontalBottom``: Calculate horizontally, across bottom of map
+* ``HorizontalAverage``: Calculate horizontally, using the average of the top, middle and bottom scales
+
+"""
+# --
+Qgis.ScaleCalculationMethod.baseClass = Qgis
 QgsScaleBarSettings.Alignment = Qgis.ScaleBarAlignment
 # monkey patching scoped based enum
 QgsScaleBarSettings.AlignLeft = Qgis.ScaleBarAlignment.Left

python/PyQt6/core/auto_generated/layout/qgslayoutitemscalebar.sip.in

@@ -813,6 +813,24 @@ Ownership of ``format`` is transferred to the scalebar.
 .. seealso:: :py:func:`numericFormat`
 
 .. versionadded:: 3.12
+%End
+
+    Qgis::ScaleCalculationMethod method() const;
+%Docstring
+Returns the scale calculation method, which determines how the bar's scale will be calculated.
+
+.. seealso:: :py:func:`setMethod`
+
+.. versionadded:: 3.40
+%End
+
+    void setMethod( Qgis::ScaleCalculationMethod method );
+%Docstring
+Sets the scale calculation ``method``, which determines how the bar's scale will be calculated.
+
+.. seealso:: :py:func:`method`
+
+.. versionadded:: 3.40
 %End
 
     void update();

python/PyQt6/core/auto_generated/qgis.sip.in

@@ -2775,6 +2775,13 @@ The development version
       Unknown,
     };
 
+    enum class ScaleCalculationMethod /BaseType=IntEnum/
+    {
+      HorizontalTop,
+      HorizontalMiddle,
+      HorizontalBottom,
+      HorizontalAverage,
+    };
 
     enum class ScaleBarAlignment /BaseType=IntEnum/
       {

python/core/auto_additions/qgis.py

@@ -9586,6 +9586,23 @@
 """
 # --
 Qgis.PictureFormat.baseClass = Qgis
+# monkey patching scoped based enum
+Qgis.ScaleCalculationMethod.HorizontalTop.__doc__ = "Calculate horizontally, across top of map"
+Qgis.ScaleCalculationMethod.HorizontalMiddle.__doc__ = "Calculate horizontally, across midle of map"
+Qgis.ScaleCalculationMethod.HorizontalBottom.__doc__ = "Calculate horizontally, across bottom of map"
+Qgis.ScaleCalculationMethod.HorizontalAverage.__doc__ = "Calculate horizontally, using the average of the top, middle and bottom scales"
+Qgis.ScaleCalculationMethod.__doc__ = """Scale calculation logic.
+
+.. versionadded:: 3.40
+
+* ``HorizontalTop``: Calculate horizontally, across top of map
+* ``HorizontalMiddle``: Calculate horizontally, across midle of map
+* ``HorizontalBottom``: Calculate horizontally, across bottom of map
+* ``HorizontalAverage``: Calculate horizontally, using the average of the top, middle and bottom scales
+
+"""
+# --
+Qgis.ScaleCalculationMethod.baseClass = Qgis
 QgsScaleBarSettings.Alignment = Qgis.ScaleBarAlignment
 # monkey patching scoped based enum
 QgsScaleBarSettings.AlignLeft = Qgis.ScaleBarAlignment.Left

python/core/auto_generated/layout/qgslayoutitemscalebar.sip.in

@@ -813,6 +813,24 @@ Ownership of ``format`` is transferred to the scalebar.
 .. seealso:: :py:func:`numericFormat`
 
 .. versionadded:: 3.12
+%End
+
+    Qgis::ScaleCalculationMethod method() const;
+%Docstring
+Returns the scale calculation method, which determines how the bar's scale will be calculated.
+
+.. seealso:: :py:func:`setMethod`
+
+.. versionadded:: 3.40
+%End
+
+    void setMethod( Qgis::ScaleCalculationMethod method );
+%Docstring
+Sets the scale calculation ``method``, which determines how the bar's scale will be calculated.
+
+.. seealso:: :py:func:`method`
+
+.. versionadded:: 3.40
 %End
 
     void update();

python/core/auto_generated/qgis.sip.in

@@ -2775,6 +2775,13 @@ The development version
       Unknown,
     };
 
+    enum class ScaleCalculationMethod
+    {
+      HorizontalTop,
+      HorizontalMiddle,
+      HorizontalBottom,
+      HorizontalAverage,
+    };
 
     enum class ScaleBarAlignment
       {

src/core/layout/qgslayoutitemscalebar.cpp

@@ -290,6 +290,21 @@ void QgsLayoutItemScaleBar::disconnectCurrentMap()
   mMap = nullptr;
 }
 
+Qgis::ScaleCalculationMethod QgsLayoutItemScaleBar::method() const
+{
+  return mMethod;
+}
+
+void QgsLayoutItemScaleBar::setMethod( Qgis::ScaleCalculationMethod method )
+{
+  if ( mMethod == method )
+    return;
+
+  mMethod = method;
+  refreshSegmentMillimeters();
+  resizeToMinimumWidth();
+}
+
 void QgsLayoutItemScaleBar::refreshUnitsPerSegment( const QgsExpressionContext *context )
 {
   if ( mDataDefinedProperties.isActive( QgsLayoutObject::DataDefinedProperty::ScalebarSegmentWidth ) )
@@ -570,19 +585,62 @@ double QgsLayoutItemScaleBar::mapWidth() const
     da.setEllipsoid( mLayout->project()->ellipsoid() );
 
     const Qgis::DistanceUnit units = da.lengthUnits();
-    double measure = 0;
-    try
+
+    QList< double > yValues;
+    switch ( mMethod )
     {
-      measure = da.measureLine( QgsPointXY( mapExtent.xMinimum(), mapExtent.yMinimum() ),
-                                QgsPointXY( mapExtent.xMaximum(), mapExtent.yMinimum() ) );
-      measure /= QgsUnitTypes::fromUnitToUnitFactor( mSettings.units(), units );
+      case Qgis::ScaleCalculationMethod::HorizontalTop:
+        yValues << mapExtent.yMaximum();
+        break;
+
+      case Qgis::ScaleCalculationMethod::HorizontalMiddle:
+        yValues << 0.5 * ( mapExtent.yMaximum() + mapExtent.yMinimum() );
+        break;
+
+
+      case Qgis::ScaleCalculationMethod::HorizontalBottom:
+        yValues << mapExtent.yMinimum();
+        break;
+
+      case Qgis::ScaleCalculationMethod::HorizontalAverage:
+        yValues << mapExtent.yMaximum();
+        yValues << 0.5 * ( mapExtent.yMaximum() + mapExtent.yMinimum() );
+        yValues << mapExtent.yMinimum();
+        break;
     }
-    catch ( QgsCsException & )
+
+    double sumValidMeasures = 0;
+    int validMeasureCount = 0;
+
+    for ( const double y : std::as_const( yValues ) )
     {
-      // TODO report errors to user
-      QgsDebugError( QStringLiteral( "An error occurred while calculating length" ) );
+      try
+      {
+        double measure = da.measureLine( QgsPointXY( mapExtent.xMinimum(), y ),
+                                         QgsPointXY( mapExtent.xMaximum(), y ) );
+        if ( std::isnan( measure ) )
+        {
+          // TODO report errors to user
+          QgsDebugError( QStringLiteral( "An error occurred while calculating length" ) );
+          continue;
+        }
+
+        measure /= QgsUnitTypes::fromUnitToUnitFactor( mSettings.units(), units );
+        sumValidMeasures += measure;
+        validMeasureCount++;
+      }
+      catch ( QgsCsException & )
+      {
+        // TODO report errors to user
+        QgsDebugError( QStringLiteral( "An error occurred while calculating length" ) );
+        continue;
+      }
     }
-    return measure;
+
+    if ( validMeasureCount == 0 )
+      return std::numeric_limits< double >::quiet_NaN();
+
+    return sumValidMeasures / validMeasureCount;
   }
 }
 
@@ -965,6 +1023,7 @@ bool QgsLayoutItemScaleBar::writePropertiesToElement( QDomElement &composerScale
   composerScaleBarElem.setAttribute( QStringLiteral( "maxBarWidth" ), mSettings.maximumBarWidth() );
   composerScaleBarElem.setAttribute( QStringLiteral( "segmentMillimeters" ), QString::number( mSegmentMillimeters ) );
   composerScaleBarElem.setAttribute( QStringLiteral( "numMapUnitsPerScaleBarUnit" ), QString::number( mSettings.mapUnitsPerScaleBarUnit() ) );
+  composerScaleBarElem.setAttribute( QStringLiteral( "method" ), qgsEnumValueToKey( mMethod ) );
 
   const QDomElement textElem = mSettings.textFormat().writeXml( doc, rwContext );
   composerScaleBarElem.appendChild( textElem );
@@ -1092,6 +1151,9 @@ bool QgsLayoutItemScaleBar::readPropertiesFromElement( const QDomElement &itemEl
   mSegmentMillimeters = itemElem.attribute( QStringLiteral( "segmentMillimeters" ), QStringLiteral( "0.0" ) ).toDouble();
   mSettings.setMapUnitsPerScaleBarUnit( itemElem.attribute( QStringLiteral( "numMapUnitsPerScaleBarUnit" ), QStringLiteral( "1.0" ) ).toDouble() );
 
+  // default to horizontal bottom to keep same behavior for older projects
+  mMethod = qgsEnumKeyToValue( itemElem.attribute( QStringLiteral( "method" ) ), Qgis::ScaleCalculationMethod::HorizontalBottom );
+
   const QDomElement lineSymbolElem = itemElem.firstChildElement( QStringLiteral( "lineSymbol" ) );
   bool foundLineSymbol = false;
   if ( !lineSymbolElem.isNull() )

src/core/layout/qgslayoutitemscalebar.h

@@ -648,6 +648,22 @@ class CORE_EXPORT QgsLayoutItemScaleBar: public QgsLayoutItem
      */
     void setNumericFormat( QgsNumericFormat *format SIP_TRANSFER );
 
+    /**
+     * Returns the scale calculation method, which determines how the bar's scale will be calculated.
+     *
+     * \see setMethod()
+     * \since QGIS 3.40
+     */
+    Qgis::ScaleCalculationMethod method() const;
+
+    /**
+     * Sets the scale calculation \a method, which determines how the bar's scale will be calculated.
+     *
+     * \see method()
+     * \since QGIS 3.40
+     */
+    void setMethod( Qgis::ScaleCalculationMethod method );
+
     /**
      * Adjusts the scale bar box size and updates the item.
      */
@@ -675,6 +691,7 @@ class CORE_EXPORT QgsLayoutItemScaleBar: public QgsLayoutItem
     QString mMapUuid;
 
     QgsScaleBarSettings mSettings;
+    Qgis::ScaleCalculationMethod mMethod = Qgis::ScaleCalculationMethod::HorizontalAverage;
 
     //! Scalebar style
     std::unique_ptr< QgsScaleBarRenderer > mStyle;

src/core/qgis.h

@@ -4875,6 +4875,19 @@ class CORE_EXPORT Qgis
     };
     Q_ENUM( PictureFormat )
 
+    /**
+     * Scale calculation logic.
+     *
+     * \since QGIS 3.40
+     */
+    enum class ScaleCalculationMethod : int
+    {
+      HorizontalTop = 0, //!< Calculate horizontally, across top of map
+      HorizontalMiddle, //!< Calculate horizontally, across midle of map
+      HorizontalBottom, //!< Calculate horizontally, across bottom of map
+      HorizontalAverage, //!< Calculate horizontally, using the average of the top, middle and bottom scales
+    };
+    Q_ENUM( ScaleCalculationMethod )
 
     /**
      * Scalebar alignment.

src/gui/layout/qgslayoutscalebarwidget.cpp

@@ -55,6 +55,20 @@ QgsLayoutScaleBarWidget::QgsLayoutScaleBarWidget( QgsLayoutItemScaleBar *scaleBa
   connect( mMinWidthSpinBox, static_cast < void ( QDoubleSpinBox::* )( double ) > ( &QDoubleSpinBox::valueChanged ), this, &QgsLayoutScaleBarWidget::mMinWidthSpinBox_valueChanged );
   connect( mMaxWidthSpinBox, static_cast < void ( QDoubleSpinBox::* )( double ) > ( &QDoubleSpinBox::valueChanged ), this, &QgsLayoutScaleBarWidget::mMaxWidthSpinBox_valueChanged );
   connect( mNumberFormatPushButton, &QPushButton::clicked, this, &QgsLayoutScaleBarWidget::changeNumberFormat );
+  connect( mMethodCombo, qOverload<int>( &QComboBox::currentIndexChanged ), this, [ = ]
+  {
+    if ( !mScalebar )
+    {
+      return;
+    }
+
+    disconnectUpdateSignal();
+    mScalebar->beginCommand( tr( "Set Scalebar Method" ) );
+    mScalebar->setMethod( mMethodCombo->currentData().value< Qgis::ScaleCalculationMethod >() );
+    mScalebar->update();
+    connectUpdateSignal();
+    mScalebar->endCommand();
+  } );
 
   registerDataDefinedButton( mSegmentsLeftDDBtn, QgsLayoutObject::DataDefinedProperty::ScalebarLeftSegments );
   registerDataDefinedButton( mSegmentsRightDDBtn, QgsLayoutObject::DataDefinedProperty::ScalebarRightSegments );
@@ -115,6 +129,11 @@ QgsLayoutScaleBarWidget::QgsLayoutScaleBarWidget( QgsLayoutItemScaleBar *scaleBa
   mUnitsComboBox->addItem( tr( "Millimeters" ), static_cast< int >( Qgis::DistanceUnit::Millimeters ) );
   mUnitsComboBox->addItem( tr( "Inches" ), static_cast< int >( Qgis::DistanceUnit::Inches ) );
 
+  mMethodCombo->addItem( tr( "Average Top, Middle and Bottom Scales" ), QVariant::fromValue( Qgis::ScaleCalculationMethod::HorizontalAverage ) );
+  mMethodCombo->addItem( tr( "Calculate along Top of Map" ), QVariant::fromValue( Qgis::ScaleCalculationMethod::HorizontalTop ) );
+  mMethodCombo->addItem( tr( "Calculate along Middle of Map" ), QVariant::fromValue( Qgis::ScaleCalculationMethod::HorizontalMiddle ) );
+  mMethodCombo->addItem( tr( "Calculate along Bottom of Map" ), QVariant::fromValue( Qgis::ScaleCalculationMethod::HorizontalBottom ) );
+
   mLineStyleButton->setSymbolType( Qgis::SymbolType::Line );
   connect( mLineStyleButton, &QgsSymbolButton::changed, this, &QgsLayoutScaleBarWidget::lineSymbolChanged );
 
@@ -349,6 +368,8 @@ void QgsLayoutScaleBarWidget::setGuiElements()
   mMinWidthSpinBox->setValue( mScalebar->minimumBarWidth() );
   mMaxWidthSpinBox->setValue( mScalebar->maximumBarWidth() );
 
+  mMethodCombo->setCurrentIndex( mMethodCombo->findData( QVariant::fromValue( mScalebar->method() ) ) );
+
   populateDataDefinedButtons();
 
   blockMemberSignals( false );
@@ -745,6 +766,7 @@ void QgsLayoutScaleBarWidget::blockMemberSignals( bool block )
   mFontButton->blockSignals( block );
   mMinWidthSpinBox->blockSignals( block );
   mMaxWidthSpinBox->blockSignals( block );
+  mMethodCombo->blockSignals( block );
 }
 
 void QgsLayoutScaleBarWidget::connectUpdateSignal()