Add API to QgsCoordinateTransform to control fallback availability

on a transform-by-transform basis, populate correctly from context

python/core/auto_generated/qgscoordinatetransform.sip.in

@@ -350,6 +350,40 @@ coordinates.
 .. seealso:: :py:func:`coordinateOperation`
 
 .. versionadded:: 3.8
+%End
+
+    void setAllowFallbackTransforms( bool allowed );
+%Docstring
+Sets whether "ballpark" fallback transformations can be used in the case that the specified
+coordinate operation fails (such as when coordinates from outside a required grid shift file
+are transformed). See fallbackOperationOccurred() for further details.
+
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+
+.. seealso:: :py:func:`allowFallbackTransforms`
+
+.. seealso:: :py:func:`setBallparkTransformsAreAppropriate`
+
+.. versionadded:: 3.12
+%End
+
+    bool allowFallbackTransforms() const;
+%Docstring
+Returns whether "ballpark" fallback transformations will be used in the case that the specified
+coordinate operation fails (such as when coordinates from outside a required grid shift file
+are transformed). See fallbackOperationOccurred() for further details.
+
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+
+.. seealso:: :py:func:`setAllowFallbackTransforms`
+
+.. seealso:: :py:func:`setBallparkTransformsAreAppropriate`
+
+.. versionadded:: 3.12
 %End
 
     void setBallparkTransformsAreAppropriate( bool appropriate );
@@ -374,11 +408,18 @@ If ``appropriate`` is ``False`` (the default behavior), then transforms MAY STIL
 when the preferred or user-specified operation fails, however whenever this occurs
 a user-visible warning will be generated.
 
+If allowFallbackTransforms() is ``False`` then this setting has no effect.
+
 .. warning::
 
    This setting applies to a single instance of a coordinate transform only,
    and is not copied when a coordinate transform object is copied or assigned.
 
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+
+
 .. versionadded:: 3.12
 %End
 
@@ -394,6 +435,11 @@ operation occurred by testing fallbackOperationOccurred() immediately after a tr
    This setting applies to a single instance of a coordinate transform only,
    and is not copied when a coordinate transform object is copied or assigned.
 
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will never perform fallback operations.
+
+
 .. seealso:: :py:func:`fallbackOperationOccurred`
 
 .. versionadded:: 3.12
@@ -403,6 +449,10 @@ operation occurred by testing fallbackOperationOccurred() immediately after a tr
 %Docstring
 Returns ``True`` if a fallback operation occurred for the most recent transform.
 
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will never perform fallback operations.
+
 .. seealso:: :py:func:`disableFallbackOperationHandler`
 
 .. versionadded:: 3.12

src/core/qgscoordinatetransform.cpp

@@ -74,7 +74,7 @@ QgsCoordinateTransform::QgsCoordinateTransform( const QgsCoordinateReferenceSyst
 
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -99,7 +99,7 @@ QgsCoordinateTransform::QgsCoordinateTransform( const QgsCoordinateReferenceSyst
 
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -122,7 +122,7 @@ QgsCoordinateTransform::QgsCoordinateTransform( const QgsCoordinateReferenceSyst
 
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -164,7 +164,7 @@ void QgsCoordinateTransform::setSourceCrs( const QgsCoordinateReferenceSystem &c
   d->calculateTransforms( mContext );
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -184,7 +184,7 @@ void QgsCoordinateTransform::setDestinationCrs( const QgsCoordinateReferenceSyst
   d->calculateTransforms( mContext );
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -208,7 +208,7 @@ void QgsCoordinateTransform::setContext( const QgsCoordinateTransformContext &co
   d->calculateTransforms( mContext );
   Q_NOWARN_DEPRECATED_PUSH
 #if PROJ_VERSION_MAJOR>=6
-  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation ) )
+  if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mProjCoordinateOperation, d->mAllowFallbackTransforms ) )
 #else
   if ( !setFromCache( d->mSourceCRS, d->mDestCRS, d->mSourceDatumTransform, d->mDestinationDatumTransform ) )
 #endif
@@ -743,7 +743,7 @@ void QgsCoordinateTransform::transformCoords( int numPoints, double *x, double *
 #if PROJ_VERSION_MAJOR>=6
 
   mFallbackOperationOccurred = false;
-  if ( actualRes != 0 )
+  if ( actualRes != 0 && d->mAllowFallbackTransforms )
   {
     // fail #1 -- try with getting proj to auto-pick an appropriate coordinate operation for the points
     if ( PJ *transform = d->threadLocalFallbackProjData() )
@@ -901,6 +901,17 @@ void QgsCoordinateTransform::setCoordinateOperation( const QString &operation )
   d->mShouldReverseCoordinateOperation = false;
 }
 
+void QgsCoordinateTransform::setAllowFallbackTransforms( bool allowed )
+{
+  d.detach();
+  d->mAllowFallbackTransforms = allowed;
+}
+
+bool QgsCoordinateTransform::allowFallbackTransforms() const
+{
+  return d->mAllowFallbackTransforms;
+}
+
 void QgsCoordinateTransform::setBallparkTransformsAreAppropriate( bool appropriate )
 {
   mBallparkTransformsAreAppropriate = appropriate;
@@ -929,7 +940,7 @@ const char *finder( const char *name )
 }
 
 #if PROJ_VERSION_MAJOR>=6
-bool QgsCoordinateTransform::setFromCache( const QgsCoordinateReferenceSystem &src, const QgsCoordinateReferenceSystem &dest, const QString &coordinateOperationProj )
+bool QgsCoordinateTransform::setFromCache( const QgsCoordinateReferenceSystem &src, const QgsCoordinateReferenceSystem &dest, const QString &coordinateOperationProj, bool allowFallback )
 {
   if ( !src.isValid() || !dest.isValid() )
     return false;
@@ -949,7 +960,7 @@ bool QgsCoordinateTransform::setFromCache( const QgsCoordinateReferenceSystem &s
   const QList< QgsCoordinateTransform > values = sTransforms.values( qMakePair( sourceKey, destKey ) );
   for ( auto valIt = values.constBegin(); valIt != values.constEnd(); ++valIt )
   {
-    if ( ( *valIt ).coordinateOperation() == coordinateOperationProj )
+    if ( ( *valIt ).coordinateOperation() == coordinateOperationProj && ( *valIt ).allowFallbackTransforms() == allowFallback )
     {
       // need to save, and then restore the context... we don't want this to be cached or to use the values from the cache
       QgsCoordinateTransformContext context = mContext;

src/core/qgscoordinatetransform.h

@@ -380,6 +380,32 @@ class CORE_EXPORT QgsCoordinateTransform
      */
     void setCoordinateOperation( const QString &operation ) const;
 
+    /**
+     * Sets whether "ballpark" fallback transformations can be used in the case that the specified
+     * coordinate operation fails (such as when coordinates from outside a required grid shift file
+     * are transformed). See fallbackOperationOccurred() for further details.
+     *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+     *
+     * \see allowFallbackTransforms()
+     * \see setBallparkTransformsAreAppropriate()
+     * \since QGIS 3.12
+     */
+    void setAllowFallbackTransforms( bool allowed );
+
+    /**
+     * Returns whether "ballpark" fallback transformations will be used in the case that the specified
+     * coordinate operation fails (such as when coordinates from outside a required grid shift file
+     * are transformed). See fallbackOperationOccurred() for further details.
+     *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+     *
+     * \see setAllowFallbackTransforms()
+     * \see setBallparkTransformsAreAppropriate()
+     * \since QGIS 3.12
+     */
+    bool allowFallbackTransforms() const;
+
     /**
      * Sets whether approximate "ballpark" results are appropriate for this coordinate transform.
      *
@@ -401,9 +427,13 @@ class CORE_EXPORT QgsCoordinateTransform
      * when the preferred or user-specified operation fails, however whenever this occurs
      * a user-visible warning will be generated.
      *
+     * If allowFallbackTransforms() is FALSE then this setting has no effect.
+     *
      * \warning This setting applies to a single instance of a coordinate transform only,
      * and is not copied when a coordinate transform object is copied or assigned.
      *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will ignore this setting.
+     *
      * \since QGIS 3.12
      */
     void setBallparkTransformsAreAppropriate( bool appropriate );
@@ -417,6 +447,8 @@ class CORE_EXPORT QgsCoordinateTransform
      * \warning This setting applies to a single instance of a coordinate transform only,
      * and is not copied when a coordinate transform object is copied or assigned.
      *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will never perform fallback operations.
+     *
      * \see fallbackOperationOccurred()
      * \since QGIS 3.12
      */
@@ -425,6 +457,8 @@ class CORE_EXPORT QgsCoordinateTransform
     /**
      * Returns TRUE if a fallback operation occurred for the most recent transform.
      *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will never perform fallback operations.
+     *
      * \see disableFallbackOperationHandler()
      * \since QGIS 3.12
      */
@@ -647,7 +681,7 @@ class CORE_EXPORT QgsCoordinateTransform
 #if PROJ_VERSION_MAJOR>=6
     bool setFromCache( const QgsCoordinateReferenceSystem &src,
                        const QgsCoordinateReferenceSystem &dest,
-                       const QString &coordinateOperationProj );
+                       const QString &coordinateOperationProj, bool allowFallback );
 #else
     bool setFromCache( const QgsCoordinateReferenceSystem &src,
                        const QgsCoordinateReferenceSystem &dest,

src/core/qgscoordinatetransform_p.cpp

@@ -107,6 +107,7 @@ QgsCoordinateTransformPrivate::QgsCoordinateTransformPrivate( const QgsCoordinat
   , mDestinationDatumTransform( other.mDestinationDatumTransform )
   , mProjCoordinateOperation( other.mProjCoordinateOperation )
   , mShouldReverseCoordinateOperation( other.mShouldReverseCoordinateOperation )
+  , mAllowFallbackTransforms( other.mAllowFallbackTransforms )
   , mIsReversed( other.mIsReversed )
 {
 #if PROJ_VERSION_MAJOR < 6
@@ -263,6 +264,7 @@ void QgsCoordinateTransformPrivate::calculateTransforms( const QgsCoordinateTran
 #if PROJ_VERSION_MAJOR >= 6
   mProjCoordinateOperation = context.calculateCoordinateOperation( mSourceCRS, mDestCRS );
   mShouldReverseCoordinateOperation = context.mustReverseCoordinateOperation( mSourceCRS, mDestCRS );
+  mAllowFallbackTransforms = context.allowFallbackTransform( mSourceCRS, mDestCRS );
 #else
   Q_NOWARN_DEPRECATED_PUSH
   QgsDatumTransform::TransformPair transforms = context.calculateDatumTransforms( mSourceCRS, mDestCRS );

src/core/qgscoordinatetransform_p.h

@@ -134,6 +134,7 @@ class QgsCoordinateTransformPrivate : public QSharedData
     Q_DECL_DEPRECATED int mDestinationDatumTransform = -1;
     QString mProjCoordinateOperation;
     bool mShouldReverseCoordinateOperation = false;
+    bool mAllowFallbackTransforms = true;
 
     //! True if the proj transform corresponds to the reverse direction, and must be flipped when transforming...
     bool mIsReversed = false;

tests/src/python/test_qgscoordinatetransform.py

@@ -149,9 +149,20 @@ def testContextProj6(self):
 
         transform = QgsCoordinateTransform(QgsCoordinateReferenceSystem('EPSG:28354'), QgsCoordinateReferenceSystem('EPSG:28353'), context)
         self.assertEqual(list(transform.context().coordinateOperations().keys()), [('EPSG:28356', 'EPSG:4283')])
-
         # should be no coordinate operation
         self.assertEqual(transform.coordinateOperation(), '')
+        # should default to allowing fallback transforms
+        self.assertTrue(transform.allowFallbackTransforms())
+
+        transform = QgsCoordinateTransform(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                           QgsCoordinateReferenceSystem('EPSG:4283'), context)
+        self.assertTrue(transform.allowFallbackTransforms())
+        context.addCoordinateOperation(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                       QgsCoordinateReferenceSystem('EPSG:4283'),
+                                       'proj', False)
+        transform = QgsCoordinateTransform(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                           QgsCoordinateReferenceSystem('EPSG:4283'), context)
+        self.assertFalse(transform.allowFallbackTransforms())
 
         # matching source
         transform = QgsCoordinateTransform(QgsCoordinateReferenceSystem('EPSG:28356'), QgsCoordinateReferenceSystem('EPSG:28353'), context)
@@ -168,6 +179,10 @@ def testContextProj6(self):
         # test manual overwriting
         transform.setCoordinateOperation('proj2')
         self.assertEqual(transform.coordinateOperation(), 'proj2')
+        transform.setAllowFallbackTransforms(False)
+        self.assertFalse(transform.allowFallbackTransforms())
+        transform.setAllowFallbackTransforms(True)
+        self.assertTrue(transform.allowFallbackTransforms())
 
         # test that auto operation setting occurs when updating src/dest crs
         transform.setSourceCrs(QgsCoordinateReferenceSystem('EPSG:28356'))