Start on QgsCoordinateTransformContext

Stores settings related to the correct datum transforms to use
when performing a coordinate transform.

python/core/conversions.sip

@@ -1742,6 +1742,112 @@ template<int, TYPE2*>
 %End
 };
 
+%MappedType QMap< QPair< QString, QString>, QPair< int, int > >
+{
+%TypeHeaderCode
+#include <QPair>
+#include <QMap>
+%End
+
+%ConvertFromTypeCode
+//convert map to a python dictionary
+  PyObject *d;
+
+  if ( ( d = PyDict_New() ) == NULL )
+    return NULL;
+
+  for ( const auto it = sipCpp->constBegin(); it != sipCpp->constEnd(); ++ it )
+  {
+    PyObject *keyobj;
+    if ( ( keyobj = PyTuple_New( 2 ) ) == NULL )
+    {
+      Py_DECREF( d );
+      return NULL;
+    }
+    PyObject *valueobj;
+    if ( ( valueobj = PyTuple_New( 2 ) ) == NULL )
+    {
+      Py_DECREF( d );
+      return NULL;
+    }
+
+    // build key
+    PyObject *k1obj = sipConvertFromNewType( new QString( it.key().first ), sipType_QString, sipTransferObj );
+    PyTuple_SetItem( keyobj, 0, k1obj );
+    PyObject *k2obj = sipConvertFromNewType( new QString( it.key().second ), sipType_QString, sipTransferObj );
+    PyTuple_SetItem( keyobj, 1, k2obj );
+
+    // build value
+    PyObject *v1obj = PyLong_FromLong( (long)( it.value().first ) );
+    PyTuple_SetItem( valueobj, 0, v1obj );
+    PyObject *v2obj = PyLong_FromLong( (long)( it.value().second ) );
+    PyTuple_SetItem( valueobj, 1, v2obj );
+
+    if(keyobj == NULL || valueobj == NULL || PyDict_SetItem(d, keyobj, valueobj) < 0)
+    {
+        Py_DECREF(d);
+
+        if (valueobj)
+        {
+            Py_DECREF(valueobj);
+        }
+
+        if (keyobj)
+        {
+            Py_DECREF(keyobj);
+        }
+        return NULL;
+      }
+
+  }
+
+  return d;
+%End
+
+%ConvertToTypeCode
+  Py_ssize_t i = 0;
+
+  PyObject *t1obj, *t2obj;
+  QMap< QPair< QString, QString>, QPair< int, int > > *qm = new QMap< QPair< QString, QString>, QPair< int, int > >;
+
+  int state;
+  while (PyDict_Next(sipPy, &i, &t1obj, &t2obj))
+  {
+      PyObject *sipKeyFirst  = PyTuple_GetItem( t1obj, 0 );
+      PyObject *sipKeySecond = PyTuple_GetItem( t1obj, 1 );
+
+      PyObject *sipValueFirst  = PyTuple_GetItem( t2obj, 0 );
+      qint64 v1 = PyLong_AsLongLong(sipValueFirst);
+      PyObject *sipValueSecond = PyTuple_GetItem( t2obj, 1 );
+      qint64 v2 = PyLong_AsLongLong(sipValueSecond);
+
+      QString *k1 = reinterpret_cast<QString *>(sipConvertToType(sipKeyFirst, sipType_QString, sipTransferObj, SIP_NOT_NONE, &state, sipIsErr));
+      if (*sipIsErr)
+      {
+          sipReleaseType(k1, sipType_QString, state);
+          delete qm;
+          return 0;
+      }
+      QString *k2 = reinterpret_cast<QString *>(sipConvertToType(sipKeySecond, sipType_QString, sipTransferObj, SIP_NOT_NONE, &state, sipIsErr));
+      if (*sipIsErr)
+      {
+          sipReleaseType(k1, sipType_QString, state);
+          sipReleaseType(k2, sipType_QString, state);
+          delete qm;
+          return 0;
+      }
+
+      qm->insert( qMakePair( *k1,*k2 ), qMakePair( v1, v2 ) );
+      sipReleaseType(k1, sipType_QString, state);
+      sipReleaseType(k2, sipType_QString, state);
+  }
+
+  *sipCppPtr = qm;
+
+  return sipGetState( sipTransferObj );
+%End
+};
+
 
 template <TYPE>
 %MappedType QVector< TYPE* >

python/core/core_auto.sip

@@ -23,6 +23,7 @@
 %Include qgsconditionalstyle.sip
 %Include qgscoordinateformatter.sip
 %Include qgscoordinatetransform.sip
+%Include qgscoordinatetransformcontext.sip
 %Include qgscrscache.sip
 %Include qgsdartmeasurement.sip
 %Include qgsdatadefinedsizelegend.sip

python/core/qgscoordinatetransformcontext.sip

@@ -0,0 +1,149 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgscoordinatetransformcontext.h                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+
+class QgsCoordinateTransformContext
+{
+%Docstring
+ Contains information about the context in which a coordinate transform is executed.
+
+.. versionadded:: 3.0
+%End
+
+%TypeHeaderCode
+#include "qgscoordinatetransformcontext.h"
+%End
+  public:
+
+    QgsCoordinateTransformContext();
+%Docstring
+ Constructor for QgsCoordinateTransformContext.
+%End
+
+    void clear();
+%Docstring
+ Clears all stored transform information from the context.
+%End
+
+    QMap<QString, int> sourceDatumTransforms() const;
+%Docstring
+ Returns the stored mapping for source CRS to associated datum transform to use.
+ The map keys will be QgsCoordinateReferenceSystems.authid()s.
+
+ \warning This method should not be used to calculate the corresponding datum transforms
+ to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+ to determine this.
+
+.. seealso:: addSourceDatumTransform()
+.. seealso:: destinationDatumTransforms()
+ :rtype: QMap<str, int>
+%End
+
+    bool addSourceDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform );
+%Docstring
+ Adds a new ``transform`` to use when projecting coordinates from the specified source
+ ``crs``.
+
+ Returns true if the new transform was added successfully.
+
+ \warning Transforms set using this method may be overridden by specific source/destination
+ transforms set by addSourceDestinationDatumTransform().
+
+.. seealso:: sourceDatumTransforms()
+.. seealso:: addDestinationDatumTransform()
+ :rtype: bool
+%End
+
+    QMap< QString, int > destinationDatumTransforms() const;
+%Docstring
+ Returns the stored mapping for destination CRS to associated datum transform to use.
+ The map keys will be QgsCoordinateReferenceSystems.authid()s.
+
+ \warning This method should not be used to calculate the corresponding datum transforms
+ to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+ to determine this.
+
+.. seealso:: addDestinationDatumTransform()
+.. seealso:: sourceDatumTransforms()
+ :rtype: QMap< str, int >
+%End
+
+    bool addDestinationDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform );
+%Docstring
+ Adds a new ``transform`` to use when projecting coordinates to the specified destination
+ ``crs``.
+
+ Returns true if the new transform was added successfully.
+
+ \warning Transforms set using this method may be overridden by specific source/destination
+ transforms set by addSourceDestinationDatumTransform().
+
+.. seealso:: destinationDatumTransforms()
+.. seealso:: addSourceDatumTransform()
+ :rtype: bool
+%End
+
+    QMap< QPair< QString, QString>, QPair< int, int > > sourceDestinationDatumTransforms() const;
+%Docstring
+ Returns the stored mapping for source to destination CRS pairs to associated datum transforms to use.
+ The map keys will be QgsCoordinateReferenceSystems.authid()s.
+
+ \warning This method should not be used to calculate the corresponding datum transforms
+ to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+ to determine this.
+
+.. seealso:: addSourceDestinationDatumTransform()
+ :rtype: QMap< QPair< str, QString>, QPair< int, int > >
+%End
+
+    bool addSourceDestinationDatumTransform( const QgsCoordinateReferenceSystem &sourceCrs,
+        const QgsCoordinateReferenceSystem &destinationCrs,
+        int sourceTransform,
+        int destinationTransform );
+%Docstring
+ Adds a new ``sourceTransform`` and ``destinationTransform`` to use when projecting coordinates
+ from the the specified ``sourceCrs`` to the specified ``destinationCrs``.
+
+ Returns true if the new transform pair was added successfully.
+
+.. note::
+
+   Transforms set using this method will override any specific source or destination
+ transforms set by addSourceDatumTransform() or addDestinationDatumTransform().
+
+.. seealso:: sourceDestinationDatumTransforms()
+ :rtype: bool
+%End
+
+    QPair< int, int > calculateDatumTransforms( const QgsCoordinateReferenceSystem &source,
+        const QgsCoordinateReferenceSystem &destination ) const;
+%Docstring
+ Returns the pair of source and destination datum transforms to use
+ for a transform from the specified ``source`` CRS to ``destination`` CRS.
+
+ Returns -1 if a datum transform should not be used for the source or
+ destination.
+ :rtype: QPair< int, int >
+%End
+
+};
+
+
+
+
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgscoordinatetransformcontext.h                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

src/core/CMakeLists.txt

@@ -150,6 +150,7 @@ SET(QGIS_CORE_SRCS
   qgscoordinatereferencesystem.cpp
   qgscoordinatetransform.cpp
   qgscoordinatetransform_p.cpp
+  qgscoordinatetransformcontext.cpp
   qgscoordinateutils.cpp
   qgscredentials.cpp
   qgscrscache.cpp
@@ -854,6 +855,7 @@ SET(QGIS_CORE_HDRS
   qgsconditionalstyle.h
   qgscoordinateformatter.h
   qgscoordinatetransform.h
+  qgscoordinatetransformcontext.h
   qgscoordinateutils.h
   qgscrscache.h
   qgsdartmeasurement.h

src/core/qgscoordinatetransformcontext.cpp

@@ -0,0 +1,72 @@
+/***************************************************************************
+                         qgscoordinatetransformcontext.cpp
+                         ---------------------------------
+    begin                : November 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgscoordinatetransformcontext.h"
+
+void QgsCoordinateTransformContext::clear()
+{
+  mSourceDestDatumTransforms.clear();
+  mSourceDatumTransforms.clear();
+  mDestDatumTransforms.clear();
+}
+
+QMap<QString, int> QgsCoordinateTransformContext::sourceDatumTransforms() const
+{
+  return mSourceDatumTransforms;
+}
+
+bool QgsCoordinateTransformContext::addSourceDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform )
+{
+  if ( !crs.isValid() )
+    return false;
+
+  mSourceDatumTransforms.insert( crs.authid(), transform );
+  return true;
+}
+
+QMap<QString, int> QgsCoordinateTransformContext::destinationDatumTransforms() const
+{
+  return mDestDatumTransforms;
+}
+
+bool QgsCoordinateTransformContext::addDestinationDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform )
+{
+  if ( !crs.isValid() )
+    return false;
+
+  mDestDatumTransforms.insert( crs.authid(), transform );
+  return true;
+}
+
+QMap<QPair<QString, QString>, QPair<int, int> > QgsCoordinateTransformContext::sourceDestinationDatumTransforms() const
+{
+  return mSourceDestDatumTransforms;
+}
+
+bool QgsCoordinateTransformContext::addSourceDestinationDatumTransform( const QgsCoordinateReferenceSystem &sourceCrs, const QgsCoordinateReferenceSystem &destinationCrs, int sourceTransform, int destinationTransform )
+{
+  if ( !sourceCrs.isValid() || !destinationCrs.isValid() )
+    return false;
+
+  mSourceDestDatumTransforms.insert( qMakePair( sourceCrs.authid(), destinationCrs.authid() ), qMakePair( sourceTransform, destinationTransform ) );
+  return true;
+}
+
+QPair<int, int> QgsCoordinateTransformContext::calculateDatumTransforms( const QgsCoordinateReferenceSystem &source, const QgsCoordinateReferenceSystem &destination ) const
+{
+
+}

src/core/qgscoordinatetransformcontext.h

@@ -0,0 +1,159 @@
+/***************************************************************************
+                         qgscoordinatetransformcontext.h
+                         -------------------------------
+    begin                : November 2017
+    copyright            : (C) 2017 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSCOORDINATETRANSFORMCONTEXT_H
+#define QGSCOORDINATETRANSFORMCONTEXT_H
+
+#include "qgis_core.h"
+#include "qgis.h"
+#include "qgscoordinatereferencesystem.h"
+
+/**
+ * \class QgsCoordinateTransformContext
+ * \ingroup core
+ * Contains information about the context in which a coordinate transform is executed.
+ *
+ * \since QGIS 3.0
+*/
+
+class CORE_EXPORT QgsCoordinateTransformContext
+{
+  public:
+
+    /**
+     * Constructor for QgsCoordinateTransformContext.
+     */
+    QgsCoordinateTransformContext() = default;
+
+    /**
+     * Clears all stored transform information from the context.
+     */
+    void clear();
+
+    /**
+     * Returns the stored mapping for source CRS to associated datum transform to use.
+     * The map keys will be QgsCoordinateReferenceSystems::authid()s.
+     *
+     * \warning This method should not be used to calculate the corresponding datum transforms
+     * to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+     * to determine this.
+     *
+     * \see addSourceDatumTransform()
+     * \see destinationDatumTransforms()
+     */
+    QMap<QString, int> sourceDatumTransforms() const;
+
+    /**
+     * Adds a new \a transform to use when projecting coordinates from the specified source
+     * \a crs.
+     *
+     * Returns true if the new transform was added successfully.
+     *
+     * \warning Transforms set using this method may be overridden by specific source/destination
+     * transforms set by addSourceDestinationDatumTransform().
+     *
+     * \see sourceDatumTransforms()
+     * \see addDestinationDatumTransform()
+     */
+    bool addSourceDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform );
+
+    /**
+     * Returns the stored mapping for destination CRS to associated datum transform to use.
+     * The map keys will be QgsCoordinateReferenceSystems::authid()s.
+     *
+     * \warning This method should not be used to calculate the corresponding datum transforms
+     * to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+     * to determine this.
+     *
+     * \see addDestinationDatumTransform()
+     * \see sourceDatumTransforms()
+     */
+    QMap< QString, int > destinationDatumTransforms() const;
+
+    /**
+     * Adds a new \a transform to use when projecting coordinates to the specified destination
+     * \a crs.
+     *
+     * Returns true if the new transform was added successfully.
+     *
+     * \warning Transforms set using this method may be overridden by specific source/destination
+     * transforms set by addSourceDestinationDatumTransform().
+     *
+     * \see destinationDatumTransforms()
+     * \see addSourceDatumTransform()
+     */
+    bool addDestinationDatumTransform( const QgsCoordinateReferenceSystem &crs, int transform );
+
+    /**
+     * Returns the stored mapping for source to destination CRS pairs to associated datum transforms to use.
+     * The map keys will be QgsCoordinateReferenceSystems::authid()s.
+     *
+     * \warning This method should not be used to calculate the corresponding datum transforms
+     * to use for a coordinate transform. Instead, always use calculateDatumTransforms()
+     * to determine this.
+     *
+     * \see addSourceDestinationDatumTransform()
+     */
+    QMap< QPair< QString, QString>, QPair< int, int > > sourceDestinationDatumTransforms() const;
+
+    /**
+     * Adds a new \a sourceTransform and \a destinationTransform to use when projecting coordinates
+     * from the the specified \a sourceCrs to the specified \a destinationCrs.
+     *
+     * Returns true if the new transform pair was added successfully.
+     *
+     * \note Transforms set using this method will override any specific source or destination
+     * transforms set by addSourceDatumTransform() or addDestinationDatumTransform().
+     *
+     * \see sourceDestinationDatumTransforms()
+     */
+    bool addSourceDestinationDatumTransform( const QgsCoordinateReferenceSystem &sourceCrs,
+        const QgsCoordinateReferenceSystem &destinationCrs,
+        int sourceTransform,
+        int destinationTransform );
+
+    /**
+     * Returns the pair of source and destination datum transforms to use
+     * for a transform from the specified \a source CRS to \a destination CRS.
+     *
+     * Returns -1 if a datum transform should not be used for the source or
+     * destination.
+     */
+    QPair< int, int > calculateDatumTransforms( const QgsCoordinateReferenceSystem &source,
+        const QgsCoordinateReferenceSystem &destination ) const;
+
+  private:
+
+    /**
+     * Mapping for datum transforms to use for source/destination CRS pairs.
+     * Matching records from this map will take precedence over other transform maps.
+     */
+    QMap< QPair< QString, QString >, QPair< int, int > > mSourceDestDatumTransforms;
+
+    //! Mapping for datum transforms to use for source CRS
+    QMap< QString, int > mSourceDatumTransforms;
+
+    //! Mapping for datum transforms to use for destination CRS
+    QMap< QString, int > mDestDatumTransforms;
+
+};
+
+#endif // QGSCOORDINATETRANSFORMCONTEXT_H
+
+
+
+

tests/src/python/CMakeLists.txt

@@ -40,6 +40,7 @@ ADD_PYTHON_TEST(PyQgsComposerPolyline test_qgscomposerpolyline.py)
 ADD_PYTHON_TEST(PyQgsComposerView test_qgscomposerview.py)
 ADD_PYTHON_TEST(PyQgsComposition test_qgscomposition.py)
 ADD_PYTHON_TEST(PyQgsConditionalStyle test_qgsconditionalstyle.py)
+ADD_PYTHON_TEST(PyQgsCoordinateTransformContext test_qgscoordinatetransformcontext.py)
 ADD_PYTHON_TEST(PyQgsDefaultValue test_qgsdefaultvalue.py)
 ADD_PYTHON_TEST(PyQgsXmlUtils test_qgsxmlutils.py)
 ADD_PYTHON_TEST(PyQgsCoordinateTransform test_qgscoordinatetransform.py)

tests/src/python/test_qgscoordinatetransformcontext.py

@@ -0,0 +1,102 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsCoordinateTransformContext
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+__author__ = 'Nyall Dawson'
+__date__ = '11/5/2017'
+__copyright__ = 'Copyright 2017, The QGIS Project'
+# This will get replaced with a git SHA1 when you do a git archive
+__revision__ = '$Format:%H$'
+
+import qgis  # NOQA
+
+from qgis.core import (QgsCoordinateReferenceSystem,
+                       QgsCoordinateTransformContext)
+from qgis.testing import start_app, unittest
+
+app = start_app()
+
+
+class TestQgsCoordinateTransformContext(unittest.TestCase):
+
+    def testSourceDatumTransforms(self):
+        context = QgsCoordinateTransformContext()
+        self.assertEqual(context.sourceDatumTransforms(), {})
+        self.assertTrue(context.addSourceDatumTransform(QgsCoordinateReferenceSystem('EPSG:3111'), 1))
+        self.assertEqual(context.sourceDatumTransforms(), {'EPSG:3111': 1})
+        self.assertTrue(context.addSourceDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'), 2))
+        self.assertEqual(context.sourceDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 2})
+        self.assertTrue(context.addSourceDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'), 3))
+        self.assertEqual(context.sourceDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+        self.assertTrue(context.addSourceDatumTransform(QgsCoordinateReferenceSystem(28356), 3))
+        self.assertEqual(context.sourceDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+
+        # invalid crs should fail
+        self.assertFalse(context.addSourceDatumTransform(QgsCoordinateReferenceSystem(), 4))
+        self.assertEqual(context.sourceDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+
+        context.clear()
+        self.assertEqual(context.sourceDatumTransforms(), {})
+
+    def testDestDatumTransforms(self):
+        context = QgsCoordinateTransformContext()
+        self.assertEqual(context.destinationDatumTransforms(), {})
+        self.assertTrue(context.addDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:3111'), 1))
+        self.assertEqual(context.destinationDatumTransforms(), {'EPSG:3111': 1})
+        self.assertTrue(context.addDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'), 2))
+        self.assertEqual(context.destinationDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 2})
+        self.assertTrue(context.addDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'), 3))
+        self.assertEqual(context.destinationDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+        self.assertTrue(context.addDestinationDatumTransform(QgsCoordinateReferenceSystem(28356), 3))
+        self.assertEqual(context.destinationDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+
+        # invalid crs should fail
+        self.assertFalse(context.addDestinationDatumTransform(QgsCoordinateReferenceSystem(), 4))
+        self.assertEqual(context.destinationDatumTransforms(), {'EPSG:3111': 1, 'EPSG:28356': 3})
+
+        context.clear()
+        self.assertEqual(context.destinationDatumTransforms(), {})
+
+    def testSourceDestinationDatumTransforms(self):
+        context = QgsCoordinateTransformContext()
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {})
+        self.assertTrue(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:3111'),
+                                                                   QgsCoordinateReferenceSystem('EPSG:4283'), 1, 2))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2)})
+        self.assertTrue(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                                                   QgsCoordinateReferenceSystem(4283), 3, 4))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
+                                                                      ('EPSG:28356', 'EPSG:4283'): (3, 4)})
+        self.assertTrue(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                                                   QgsCoordinateReferenceSystem(28357), 7, 8))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
+                                                                      ('EPSG:28356', 'EPSG:4283'): (3, 4),
+                                                                      ('EPSG:28356', 'EPSG:28357'): (7, 8)})
+        self.assertTrue(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:28356'),
+                                                                   QgsCoordinateReferenceSystem('EPSG:28357'), 9, 11))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
+                                                                      ('EPSG:28356', 'EPSG:4283'): (3, 4),
+                                                                      ('EPSG:28356', 'EPSG:28357'): (9, 11)})
+
+        # invalid additions
+        self.assertFalse(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem(),
+                                                                    QgsCoordinateReferenceSystem('EPSG:28357'), 9, 11))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
+                                                                      ('EPSG:28356', 'EPSG:4283'): (3, 4),
+                                                                      ('EPSG:28356', 'EPSG:28357'): (9, 11)})
+        self.assertFalse(context.addSourceDestinationDatumTransform(QgsCoordinateReferenceSystem('EPSG:3111'),
+                                                                    QgsCoordinateReferenceSystem(), 9, 11))
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
+                                                                      ('EPSG:28356', 'EPSG:4283'): (3, 4),
+                                                                      ('EPSG:28356', 'EPSG:28357'): (9, 11)})
+
+        context.clear()
+        self.assertEqual(context.sourceDestinationDatumTransforms(), {})
+
+
+if __name__ == '__main__':
+    unittest.main()