Add a QgsCoordinateTransformContext member to QgsProject

python/core/qgsproject.sip

@@ -127,6 +127,18 @@ Returns the QgsProject singleton instance
 .. versionadded:: 3.0
 %End
 
+
+
+    QgsCoordinateTransformContext &transformContext();
+%Docstring
+ Returns a modifiable reference to the project's coordinate transform context, which stores various
+ information regarding which datum transforms should be used when transforming points
+ from a source to destination coordinate reference system.
+
+.. versionadded:: 3.0
+ :rtype: QgsCoordinateTransformContext
+%End
+
     void clear();
 %Docstring
  Clear the project - removes all settings and resets it back to an empty, default state.

src/core/qgsproject.cpp

@@ -471,6 +471,16 @@ void QgsProject::setEllipsoid( const QString &ellipsoid )
   emit ellipsoidChanged( ellipsoid );
 }
 
+QgsCoordinateTransformContext QgsProject::transformContext() const
+{
+  return mTransformContext;
+}
+
+QgsCoordinateTransformContext &QgsProject::transformContext()
+{
+  return mTransformContext;
+}
+
 void QgsProject::clear()
 {
   mFile.setFileName( QString() );
@@ -910,6 +920,8 @@ bool QgsProject::readProjectFile( const QString &filename )
   }
   mCrs = projectCrs;
 
+  mTransformContext.readXml( doc->documentElement(), *doc, context );
+
   QDomNodeList nl = doc->elementsByTagName( QStringLiteral( "autotransaction" ) );
   if ( nl.count() )
   {
@@ -1446,6 +1458,8 @@ bool QgsProject::writeProjectFile( const QString &filename )
 
   mLabelingEngineSettings->writeSettingsToProject( this );
 
+  mTransformContext.writeXml( qgisNode, *doc, context );
+
   QDomElement annotationsElem = mAnnotationManager->writeXml( *doc, context );
   qgisNode.appendChild( annotationsElem );
 

src/core/qgsproject.h

@@ -37,6 +37,7 @@
 #include "qgsprojectversion.h"
 #include "qgsexpressioncontextgenerator.h"
 #include "qgscoordinatereferencesystem.h"
+#include "qgscoordinatetransformcontext.h"
 #include "qgsprojectproperty.h"
 #include "qgsmaplayer.h"
 #include "qgsmaplayerstore.h"
@@ -178,6 +179,25 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void setEllipsoid( const QString &ellipsoid );
 
+
+    /**
+     * Returns a copy of the project's coordinate transform context, which stores various
+     * information regarding which datum transforms should be used when transforming points
+     * from a source to destination coordinate reference system.
+     *
+     * \since QGIS 3.0
+     */
+    QgsCoordinateTransformContext transformContext() const SIP_SKIP;
+
+    /**
+     * Returns a modifiable reference to the project's coordinate transform context, which stores various
+     * information regarding which datum transforms should be used when transforming points
+     * from a source to destination coordinate reference system.
+     *
+     * \since QGIS 3.0
+     */
+    QgsCoordinateTransformContext &transformContext();
+
     /**
      * Clear the project - removes all settings and resets it back to an empty, default state.
      * \since QGIS 2.4
@@ -1164,6 +1184,8 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
     QgsCoordinateReferenceSystem mCrs;
     bool mDirty = false;                 // project has been modified since it has been read or saved
     bool mTrustLayerMetadata = false;
+
+    QgsCoordinateTransformContext mTransformContext;
 };
 
 /**

tests/src/python/test_qgscoordinatetransformcontext.py

@@ -16,7 +16,8 @@ import qgis  # NOQA
 
 from qgis.core import (QgsCoordinateReferenceSystem,
                        QgsCoordinateTransformContext,
-                       QgsReadWriteContext)
+                       QgsReadWriteContext,
+                       QgsProject)
 from qgis.testing import start_app, unittest
 from qgis.PyQt.QtXml import QDomDocument
 
@@ -214,6 +215,14 @@ class TestQgsCoordinateTransformContext(unittest.TestCase):
         self.assertEqual(context2.sourceDestinationDatumTransforms(), {('EPSG:3111', 'EPSG:4283'): (1, 2),
                                                                        ('EPSG:28356', 'EPSG:4283'): (3, 4)})
 
+    def testProject(self):
+        """
+        Test project's transform context
+        """
+        project = QgsProject()
+        project.transformContext().addSourceDatumTransform(QgsCoordinateReferenceSystem('EPSG:3111'), 1)
+        self.assertEqual(project.transformContext().sourceDatumTransforms(), {'EPSG:3111': 1})
+
 
 if __name__ == '__main__':
     unittest.main()