Add api to allow the native format for a crs definition (i.e. wkt

or proj) to be saved when the crs is saved to xml

Allows us a way to present a custom crs in the same format as it was
originally defined using

python/core/auto_generated/proj/qgscoordinatereferencesystem.sip.in

@@ -995,6 +995,34 @@ definition. FormatWkt is recommended as it is a lossless format.
    Since QGIS 3.18, internally this calls :py:func:`QgsCoordinateReferenceSystemRegistry.addUserCrs()`.
 %End
 
+    void setNativeFormat( Qgis::CrsDefinitionFormat format );
+%Docstring
+Sets the native ``format`` for the CRS definition.
+
+.. note::
+
+   This has no effect on the underlying definition of the CRS, rather it controls what format
+   to use when displaying the CRS's definition to users.
+
+.. seealso:: :py:func:`nativeFormat`
+
+.. versionadded:: 3.24
+%End
+
+    Qgis::CrsDefinitionFormat nativeFormat() const;
+%Docstring
+Returns the native format for the CRS definition.
+
+.. note::
+
+   This has no effect on the underlying definition of the CRS, rather it controls what format
+   to use when displaying the CRS's definition to users.
+
+.. seealso:: :py:func:`setNativeFormat`
+
+.. versionadded:: 3.24
+%End
+
     QgsCoordinateReferenceSystem toGeographicCrs() const;
 %Docstring
 Returns the geographic CRS associated with this CRS object.

src/core/proj/qgscoordinatereferencesystem.cpp

@@ -124,6 +124,7 @@ QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem( const long id, CrsTy
 QgsCoordinateReferenceSystem::QgsCoordinateReferenceSystem( const QgsCoordinateReferenceSystem &srs )  //NOLINT
   : d( srs.d )
   , mValidationHint( srs.mValidationHint )
+  , mNativeFormat( srs.mNativeFormat )
 {
 }
 
@@ -131,6 +132,7 @@ QgsCoordinateReferenceSystem &QgsCoordinateReferenceSystem::operator=( const Qgs
 {
   d = srs.d;
   mValidationHint = srs.mValidationHint;
+  mNativeFormat = srs.mNativeFormat;
   return *this;
 }
 
@@ -1860,6 +1862,8 @@ bool QgsCoordinateReferenceSystem::readXml( const QDomNode &node )
     {
       d->mCoordinateEpoch = std::numeric_limits< double >::quiet_NaN();
     }
+
+    mNativeFormat = qgsEnumKeyToValue<Qgis::CrsDefinitionFormat>( srsNode.toElement().attribute( QStringLiteral( "nativeFormat" ) ), Qgis::CrsDefinitionFormat::Wkt );
   }
   else
   {
@@ -1875,6 +1879,8 @@ bool QgsCoordinateReferenceSystem::writeXml( QDomNode &node, QDomDocument &doc )
   QDomElement layerNode = node.toElement();
   QDomElement srsElement = doc.createElement( QStringLiteral( "spatialrefsys" ) );
 
+  srsElement.setAttribute( QStringLiteral( "nativeFormat" ), qgsEnumValueToKey<Qgis::CrsDefinitionFormat>( mNativeFormat ) );
+
   if ( std::isfinite( d->mCoordinateEpoch ) )
   {
     srsElement.setAttribute( QStringLiteral( "coordinateEpoch" ), d->mCoordinateEpoch );
@@ -2052,6 +2058,16 @@ long QgsCoordinateReferenceSystem::saveAsUserCrs( const QString &name, Qgis::Crs
   return QgsApplication::coordinateReferenceSystemRegistry()->addUserCrs( *this, name, nativeFormat );
 }
 
+void QgsCoordinateReferenceSystem::setNativeFormat( Qgis::CrsDefinitionFormat format )
+{
+  mNativeFormat = format;
+}
+
+Qgis::CrsDefinitionFormat QgsCoordinateReferenceSystem::nativeFormat() const
+{
+  return mNativeFormat;
+}
+
 long QgsCoordinateReferenceSystem::getRecordCount()
 {
   sqlite3_database_unique_ptr database;

src/core/proj/qgscoordinatereferencesystem.h

@@ -907,6 +907,28 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
      */
     long saveAsUserCrs( const QString &name, Qgis::CrsDefinitionFormat nativeFormat = Qgis::CrsDefinitionFormat::Wkt );
 
+    /**
+     * Sets the native \a format for the CRS definition.
+     *
+     * \note This has no effect on the underlying definition of the CRS, rather it controls what format
+     * to use when displaying the CRS's definition to users.
+     *
+     * \see nativeFormat()
+     * \since QGIS 3.24
+     */
+    void setNativeFormat( Qgis::CrsDefinitionFormat format );
+
+    /**
+     * Returns the native format for the CRS definition.
+     *
+     * \note This has no effect on the underlying definition of the CRS, rather it controls what format
+     * to use when displaying the CRS's definition to users.
+     *
+     * \see setNativeFormat()
+     * \since QGIS 3.24
+     */
+    Qgis::CrsDefinitionFormat nativeFormat() const;
+
     /**
      * Returns the geographic CRS associated with this CRS object.
      *
@@ -1092,6 +1114,8 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
 
     QString mValidationHint;
 
+    Qgis::CrsDefinitionFormat mNativeFormat = Qgis::CrsDefinitionFormat::Wkt;
+
     friend class QgsProjContext;
 
     // Only meant to be called by QgsProjContext::~QgsProjContext()

tests/src/core/testqgscoordinatereferencesystem.cpp

@@ -74,6 +74,8 @@ class TestQgsCoordinateReferenceSystem: public QObject
     void noEquality();
     void equalityInvalid();
     void readWriteXml();
+    void readWriteXmlNativeFormatWkt();
+    void readWriteXmlNativeFormatProj();
     void setCustomSrsValidation();
     void customSrsValidation();
     void postgisSrid();
@@ -1308,6 +1310,40 @@ void TestQgsCoordinateReferenceSystem::readWriteXml()
   QCOMPARE( myCrs21c.description(), QStringLiteral( "a new CRS C" ) );
 }
 
+void TestQgsCoordinateReferenceSystem::readWriteXmlNativeFormatWkt()
+{
+  QgsCoordinateReferenceSystem crs = QgsCoordinateReferenceSystem::fromProj( QStringLiteral( "+proj=ortho +lat_0=-11 +lon_0=34 +x_0=0 +y_0=0 +ellps=sphere +units=m +no_defs +type=crs" ) );
+  crs.setNativeFormat( Qgis::CrsDefinitionFormat::Wkt );
+
+  QDomDocument document( QStringLiteral( "test" ) );
+  QDomElement node = document.createElement( QStringLiteral( "crs" ) );
+  document.appendChild( node );
+
+  QVERIFY( crs.writeXml( node, document ) );
+
+  QgsCoordinateReferenceSystem crs2;
+  QVERIFY( crs2.readXml( node ) );
+  QVERIFY( crs == crs2 );
+  QCOMPARE( crs2.nativeFormat(), Qgis::CrsDefinitionFormat::Wkt );
+}
+
+void TestQgsCoordinateReferenceSystem::readWriteXmlNativeFormatProj()
+{
+  QgsCoordinateReferenceSystem crs = QgsCoordinateReferenceSystem::fromProj( QStringLiteral( "+proj=ortho +lat_0=-11.6 +lon_0=34 +x_0=0 +y_0=0 +ellps=sphere +units=m +no_defs +type=crs" ) );
+  crs.setNativeFormat( Qgis::CrsDefinitionFormat::Proj );
+
+  QDomDocument document( QStringLiteral( "test" ) );
+  QDomElement node = document.createElement( QStringLiteral( "crs" ) );
+  document.appendChild( node );
+
+  QVERIFY( crs.writeXml( node, document ) );
+
+  QgsCoordinateReferenceSystem crs2;
+  QVERIFY( crs2.readXml( node ) );
+  QVERIFY( crs == crs2 );
+  QCOMPARE( crs2.nativeFormat(), Qgis::CrsDefinitionFormat::Proj );
+}
+
 void TestQgsCoordinateReferenceSystem::setCustomSrsValidation()
 {
   //QgsCoordinateReferenceSystem myCrs;