Add method to retrieve the details of the coordinate operation which is

actually being used by a QgsCoordinateTransform object

python/core/auto_generated/qgscoordinatetransform.sip.in

@@ -293,14 +293,42 @@ Returns ``True`` if the transform short circuits because the source and destinat
 Returns a Proj string representing the coordinate operation which will be used to transform
 coordinates.
 
+.. note::
+
+   The string returned by this method gives the desired coordinate operation string, based on
+   the state of the QgsCoordinateTransformContext object given in the QgsCoordinateTransform's constructor.
+   It may be an empty string if no explicit coordinate operation is required. In order to determine the
+   ACTUAL coordinate operation which is being used by the transform, use the instantiatedCoordinateOperationDetails() call instead.
+
 .. note::
 
    Requires Proj 6.0 or later. Builds based on earlier Proj versions will always return
    an empty string, and the deprecated sourceDatumTransformId() or destinationDatumTransformId() methods should be used instead.
 
+
+.. seealso:: :py:func:`instantiatedCoordinateOperationDetails`
+
 .. seealso:: :py:func:`setCoordinateOperation`
 
 .. versionadded:: 3.8
+%End
+
+    QgsDatumTransform::TransformDetails instantiatedCoordinateOperationDetails() const;
+%Docstring
+Returns the transform details representing the coordinate operation which is being used to transform
+coordinates.
+
+This may differ from the result returned by coordinateOperation() if the desired coordinate
+operation was not successfully instantiated.
+
+.. note::
+
+   Requires Proj 6.0 or later. Builds based on earlier Proj versions will always return
+   an empty result, and the deprecated sourceDatumTransformId() or destinationDatumTransformId() methods should be used instead.
+
+.. seealso:: :py:func:`coordinateOperation`
+
+.. versionadded:: 3.10.2
 %End
 
     void setCoordinateOperation( const QString &operation ) const;

src/core/qgscoordinatetransform.cpp

@@ -799,6 +799,16 @@ QString QgsCoordinateTransform::coordinateOperation() const
   return d->mProjCoordinateOperation;
 }
 
+QgsDatumTransform::TransformDetails QgsCoordinateTransform::instantiatedCoordinateOperationDetails() const
+{
+#if PROJ_VERSION_MAJOR>=6
+  ProjData projData = d->threadLocalProjData();
+  return QgsDatumTransform::transformDetailsFromPj( projData );
+#else
+  return QgsDatumTransform::TransformDetails();
+#endif
+}
+
 void QgsCoordinateTransform::setCoordinateOperation( const QString &operation ) const
 {
   d.detach();

src/core/qgscoordinatetransform.h

@@ -336,14 +336,35 @@ class CORE_EXPORT QgsCoordinateTransform
      * Returns a Proj string representing the coordinate operation which will be used to transform
      * coordinates.
      *
+     * \note The string returned by this method gives the desired coordinate operation string, based on
+     * the state of the QgsCoordinateTransformContext object given in the QgsCoordinateTransform's constructor.
+     * It may be an empty string if no explicit coordinate operation is required. In order to determine the
+     * ACTUAL coordinate operation which is being used by the transform, use the instantiatedCoordinateOperationDetails() call instead.
+     *
      * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will always return
      * an empty string, and the deprecated sourceDatumTransformId() or destinationDatumTransformId() methods should be used instead.
      *
+     * \see instantiatedCoordinateOperationDetails()
      * \see setCoordinateOperation()
      * \since QGIS 3.8
      */
     QString coordinateOperation() const;
 
+    /**
+     * Returns the transform details representing the coordinate operation which is being used to transform
+     * coordinates.
+     *
+     * This may differ from the result returned by coordinateOperation() if the desired coordinate
+     * operation was not successfully instantiated.
+     *
+     * \note Requires Proj 6.0 or later. Builds based on earlier Proj versions will always return
+     * an empty result, and the deprecated sourceDatumTransformId() or destinationDatumTransformId() methods should be used instead.
+     *
+     * \see coordinateOperation()
+     * \since QGIS 3.10.2
+     */
+    QgsDatumTransform::TransformDetails instantiatedCoordinateOperationDetails() const;
+
     /**
      * Sets a Proj string representing the coordinate \a operation which will be used to transform
      * coordinates.

tests/src/core/testqgscoordinatetransform.cpp

@@ -22,6 +22,7 @@
 #include <QObject>
 #include "qgstest.h"
 #include "qgsexception.h"
+#include "qgslogger.h"
 
 class TestQgsCoordinateTransform: public QObject
 {