Add method to convert QgsCoordinateReferenceSystem to geodetic crs

qgis · Jan 11, 2022 · 1f240c0 · 1f240c0
1 parent e504be4
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diff --git a/python/core/auto_generated/proj/qgscoordinatereferencesystem.sip.in b/python/core/auto_generated/proj/qgscoordinatereferencesystem.sip.in
@@ -995,6 +995,17 @@ definition. FormatWkt is recommended as it is a lossless format.
    Since QGIS 3.18, internally this calls :py:func:`QgsCoordinateReferenceSystemRegistry.addUserCrs()`.
 %End
 
+    QgsCoordinateReferenceSystem toGeodeticCrs() const;
+%Docstring
+Returns the geodetic CRS associated with this CRS object.
+
+May return an invalid CRS if the geodetic CRS could not be determined.
+
+This method will always return a longitude, latitude ordered CRS.
+
+.. versionadded:: 3.24
+%End
+
     QString geographicCrsAuthId() const;
 %Docstring
 Returns auth id of related geographic CRS

diff --git a/src/core/proj/qgscoordinatereferencesystem.cpp b/src/core/proj/qgscoordinatereferencesystem.cpp
@@ -2608,6 +2608,35 @@ const QHash<long, QgsCoordinateReferenceSystem> &QgsCoordinateReferenceSystem::s
   return *sSrsIdCache();
 }
 
+QgsCoordinateReferenceSystem QgsCoordinateReferenceSystem::toGeodeticCrs() const
+{
+  if ( isGeographic() )
+  {
+    return *this;
+  }
+
+  if ( PJ *obj = d->threadLocalProjObject() )
+  {
+    PJ_CONTEXT *pjContext = QgsProjContext::get();
+    QgsProjUtils::proj_pj_unique_ptr geoCrs( proj_crs_get_geodetic_crs( pjContext, obj ) );
+    if ( !geoCrs )
+      return QgsCoordinateReferenceSystem();
+
+    if ( !testIsGeographic( geoCrs.get() ) )
+      return QgsCoordinateReferenceSystem();
+
+    QgsProjUtils::proj_pj_unique_ptr normalized( proj_normalize_for_visualization( pjContext, geoCrs.get() ) );
+    if ( !normalized )
+      return QgsCoordinateReferenceSystem();
+
+    return QgsCoordinateReferenceSystem::fromProjObject( normalized.get() );
+  }
+  else
+  {
+    return QgsCoordinateReferenceSystem();
+  }
+}
+
 QString QgsCoordinateReferenceSystem::geographicCrsAuthId() const
 {
   if ( isGeographic() )

diff --git a/src/core/proj/qgscoordinatereferencesystem.h b/src/core/proj/qgscoordinatereferencesystem.h
@@ -907,6 +907,17 @@ class CORE_EXPORT QgsCoordinateReferenceSystem
      */
     long saveAsUserCrs( const QString &name, Qgis::CrsDefinitionFormat nativeFormat = Qgis::CrsDefinitionFormat::Wkt );
 
+    /**
+     * Returns the geodetic CRS associated with this CRS object.
+     *
+     * May return an invalid CRS if the geodetic CRS could not be determined.
+     *
+     * This method will always return a longitude, latitude ordered CRS.
+     *
+     * \since QGIS 3.24
+     */
+    QgsCoordinateReferenceSystem toGeodeticCrs() const;
+
     //! Returns auth id of related geographic CRS
     QString geographicCrsAuthId() const;
 

diff --git a/tests/src/core/testqgscoordinatereferencesystem.cpp b/tests/src/core/testqgscoordinatereferencesystem.cpp
@@ -1693,9 +1693,13 @@ void TestQgsCoordinateReferenceSystem::geographicCrsAuthId()
   crs.createFromString( QStringLiteral( "EPSG:4326" ) );
   QCOMPARE( crs.authid(), QStringLiteral( "EPSG:4326" ) );
   QCOMPARE( crs.geographicCrsAuthId(), QStringLiteral( "EPSG:4326" ) );
+  QCOMPARE( crs.toGeodeticCrs(), crs );
+
   crs.createFromString( QStringLiteral( "EPSG:3825" ) );
   QCOMPARE( crs.authid(), QStringLiteral( "EPSG:3825" ) );
   QCOMPARE( crs.geographicCrsAuthId(), QStringLiteral( "EPSG:3824" ) );
+  QCOMPARE( crs.toGeodeticCrs().toProj().replace( QStringLiteral( "+towgs84=0,0,0,0,0,0,0 " ), QString() ).replace( QStringLiteral( " +type=crs" ), QString() ),
+            QgsCoordinateReferenceSystem( QStringLiteral( "EPSG:3824" ) ).toProj().replace( QStringLiteral( "+towgs84=0,0,0,0,0,0,0 " ), QString() ).replace( QStringLiteral( " +type=crs" ), QString() ) );
 }
 
 void TestQgsCoordinateReferenceSystem::noProj()