Add proj_create_conversion_pole_rotation_netcdf_cf_convention() to address netCDF datasets using a pole rotation method

9 files changed, 215 insertions, 2 deletions

diff --git a/include/proj/coordinateoperation.hpp b/include/proj/coordinateoperation.hpp
index aeef04f3..3d2ab800 100644
--- a/include/proj/coordinateoperation.hpp
+++ b/include/proj/coordinateoperation.hpp
@@ -1340,6 +1340,12 @@ class PROJ_GCC_DLL Conversion : public SingleOperation {
         const common::Angle &southPoleLongInUnrotatedCRS,
         const common::Angle &axisRotation);
 
+    PROJ_DLL static ConversionNNPtr createPoleRotationNetCDFCFConvention(
+        const util::PropertyMap &properties,
+        const common::Angle &gridNorthPoleLatitude,
+        const common::Angle &gridNorthPoleLongitude,
+        const common::Angle &northPoleGridLongitude);
+
     PROJ_DLL static ConversionNNPtr
     createChangeVerticalUnit(const util::PropertyMap &properties,
                              const common::Scale &factor);
diff --git a/scripts/reference_exported_symbols.txt b/scripts/reference_exported_symbols.txt
index 9b84c09b..d49a59b2 100644
--- a/scripts/reference_exported_symbols.txt
+++ b/scripts/reference_exported_symbols.txt
@@ -571,6 +571,7 @@ osgeo::proj::operation::Conversion::create(osgeo::proj::util::PropertyMap const&
 osgeo::proj::operation::Conversion::createPolarStereographicVariantA(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Scale const&, osgeo::proj::common::Length const&, osgeo::proj::common::Length const&)
 osgeo::proj::operation::Conversion::createPolarStereographicVariantB(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Length const&, osgeo::proj::common::Length const&)
 osgeo::proj::operation::Conversion::createPoleRotationGRIBConvention(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&)
+osgeo::proj::operation::Conversion::createPoleRotationNetCDFCFConvention(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&)
 osgeo::proj::operation::Conversion::createPopularVisualisationPseudoMercator(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Length const&, osgeo::proj::common::Length const&)
 osgeo::proj::operation::Conversion::createQuadrilateralizedSphericalCube(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Length const&, osgeo::proj::common::Length const&)
 osgeo::proj::operation::Conversion::createRobinson(osgeo::proj::util::PropertyMap const&, osgeo::proj::common::Angle const&, osgeo::proj::common::Length const&, osgeo::proj::common::Length const&)
@@ -884,6 +885,7 @@ proj_create_conversion_orthographic
 proj_create_conversion_polar_stereographic_variant_a
 proj_create_conversion_polar_stereographic_variant_b
 proj_create_conversion_pole_rotation_grib_convention
+proj_create_conversion_pole_rotation_netcdf_cf_convention
 proj_create_conversion_popular_visualisation_pseudo_mercator
 proj_create_conversion_quadrilateralized_spherical_cube
 proj_create_conversion_robinson
diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index ace699e4..1bf6cbf0 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -7085,6 +7085,37 @@ PJ *proj_create_conversion_pole_rotation_grib_convention(
     return nullptr;
 }
 
+// ---------------------------------------------------------------------------
+
+/** \brief Instantiate a conversion based on the Pole Rotation method, using
+ * the conventions of the netCDF CF convention for the netCDF format.
+ *
+ * See
+ * osgeo::proj::operation::Conversion::createPoleRotationNetCDFCFConvention().
+ *
+ * Linear parameters are expressed in (linear_unit_name,
+ * linear_unit_conv_factor).
+ * Angular parameters are expressed in (ang_unit_name, ang_unit_conv_factor).
+ */
+PJ *proj_create_conversion_pole_rotation_netcdf_cf_convention(
+    PJ_CONTEXT *ctx, double grid_north_pole_latitude,
+    double grid_north_pole_longitude, double north_pole_grid_longitude,
+    const char *ang_unit_name, double ang_unit_conv_factor) {
+    SANITIZE_CTX(ctx);
+    try {
+        UnitOfMeasure angUnit(
+            createAngularUnit(ang_unit_name, ang_unit_conv_factor));
+        auto conv = Conversion::createPoleRotationNetCDFCFConvention(
+            PropertyMap(), Angle(grid_north_pole_latitude, angUnit),
+            Angle(grid_north_pole_longitude, angUnit),
+            Angle(north_pole_grid_longitude, angUnit));
+        return proj_create_conversion(ctx, conv);
+    } catch (const std::exception &e) {
+        proj_log_error(ctx, __FUNCTION__, e.what());
+    }
+    return nullptr;
+}
+
 /* END: Generated by scripts/create_c_api_projections.py*/
 
 // ---------------------------------------------------------------------------
diff --git a/src/iso19111/crs.cpp b/src/iso19111/crs.cpp
index 3e825ff0..a15758ab 100644
--- a/src/iso19111/crs.cpp
+++ b/src/iso19111/crs.cpp
@@ -5983,7 +5983,9 @@ void DerivedGeographicCRS::_exportToPROJString(
     }
 
     if (ci_equal(methodName,
-                 PROJ_WKT2_NAME_METHOD_POLE_ROTATION_GRIB_CONVENTION)) {
+                 PROJ_WKT2_NAME_METHOD_POLE_ROTATION_GRIB_CONVENTION) ||
+        ci_equal(methodName,
+                 PROJ_WKT2_NAME_METHOD_POLE_ROTATION_NETCDF_CF_CONVENTION)) {
         l_conv->_exportToPROJString(formatter);
         return;
     }
diff --git a/src/iso19111/operation/conversion.cpp b/src/iso19111/operation/conversion.cpp
index e884db3c..3cc452f8 100644
--- a/src/iso19111/operation/conversion.cpp
+++ b/src/iso19111/operation/conversion.cpp
@@ -2227,6 +2227,51 @@ ConversionNNPtr Conversion::createPoleRotationGRIBConvention(
 
 // ---------------------------------------------------------------------------
 
+/** \brief Instantiate a conversion based on the Pole Rotation method, using
+ * the conventions of the netCDF CF convention for the netCDF format.
+ *
+ * Those are mentioned in the Note 2 of
+ * https://cfconventions.org/Data/cf-conventions/cf-conventions-1.8/cf-conventions.html#_rotated_pole
+ *
+ * Several conventions for the pole rotation method exists.
+ * The parameters provided in this method are remapped to the PROJ ob_tran
+ * operation with:
+ * <pre>
+ * +proj=ob_tran +o_proj=longlat +o_lon_p=northPoleGridLongitude
+ *                               +o_lat_p=gridNorthPoleLatitude
+ *                               +lon_0=180+gridNorthPoleLongitude
+ * </pre>
+ *
+ * Another implementation of that convention is also in the netcdf-java library:
+ * https://github.com/Unidata/netcdf-java/blob/3ce72c0cd167609ed8c69152bb4a004d1daa9273/cdm/core/src/main/java/ucar/unidata/geoloc/projection/RotatedPole.java
+ *
+ * The PROJ implementation of this method assumes a spherical ellipsoid.
+ *
+ * @param properties See \ref general_properties of the conversion. If the name
+ * is not provided, it is automatically set.
+ * @param gridNorthPoleLatitude True latitude of the north pole of the rotated
+ * grid
+ * @param gridNorthPoleLongitude True longitude of the north pole of the rotated
+ * grid.
+ * @param northPoleGridLongitude Longitude of the true north pole in the rotated
+ * grid.
+ * @return a new Conversion.
+ *
+ * @since 8.2
+ */
+ConversionNNPtr Conversion::createPoleRotationNetCDFCFConvention(
+    const util::PropertyMap &properties,
+    const common::Angle &gridNorthPoleLatitude,
+    const common::Angle &gridNorthPoleLongitude,
+    const common::Angle &northPoleGridLongitude) {
+    return create(properties,
+                  PROJ_WKT2_NAME_METHOD_POLE_ROTATION_NETCDF_CF_CONVENTION,
+                  createParams(gridNorthPoleLatitude, gridNorthPoleLongitude,
+                               northPoleGridLongitude));
+}
+
+// ---------------------------------------------------------------------------
+
 /** \brief Instantiate a conversion based on the Change of Vertical Unit
  * method.
  *
@@ -3628,6 +3673,24 @@ void Conversion::_exportToPROJString(
         formatter->addParam("o_lat_p", -southPoleLat);
         formatter->addParam("lon_0", southPoleLon);
         bConversionDone = true;
+    } else if (ci_equal(
+                   methodName,
+                   PROJ_WKT2_NAME_METHOD_POLE_ROTATION_NETCDF_CF_CONVENTION)) {
+        double gridNorthPoleLatitude = parameterValueNumeric(
+            PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LATITUDE_NETCDF_CONVENTION,
+            common::UnitOfMeasure::DEGREE);
+        double gridNorthPoleLongitude = parameterValueNumeric(
+            PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LONGITUDE_NETCDF_CONVENTION,
+            common::UnitOfMeasure::DEGREE);
+        double northPoleGridLongitude = parameterValueNumeric(
+            PROJ_WKT2_NAME_PARAMETER_NORTH_POLE_GRID_LONGITUDE_NETCDF_CONVENTION,
+            common::UnitOfMeasure::DEGREE);
+        formatter->addStep("ob_tran");
+        formatter->addParam("o_proj", "longlat");
+        formatter->addParam("o_lon_p", northPoleGridLongitude);
+        formatter->addParam("o_lat_p", gridNorthPoleLatitude);
+        formatter->addParam("lon_0", 180 + gridNorthPoleLongitude);
+        bConversionDone = true;
     } else if (ci_equal(methodName, "Adams_Square_II")) {
         // Look for ESRI method and parameter names (to be opposed
         // to the OGC WKT2 names we use elsewhere, because there's no mapping
diff --git a/src/iso19111/operation/parammappings.cpp b/src/iso19111/operation/parammappings.cpp
index 5999d535..9acc9e93 100644
--- a/src/iso19111/operation/parammappings.cpp
+++ b/src/iso19111/operation/parammappings.cpp
@@ -1305,6 +1305,22 @@ static const ParamMapping *const paramsPoleRotationGRIBConvention[] = {
     &paramSouthPoleLatGRIB, &paramSouthPoleLonGRIB, &paramAxisRotationGRIB,
     nullptr};
 
+static const ParamMapping paramGridNorthPoleLatitudeNetCDF = {
+    PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LATITUDE_NETCDF_CONVENTION, 0,
+    nullptr, common::UnitOfMeasure::Type::ANGULAR, nullptr};
+
+static const ParamMapping paramGridNorthPoleLongitudeNetCDF = {
+    PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LONGITUDE_NETCDF_CONVENTION, 0,
+    nullptr, common::UnitOfMeasure::Type::ANGULAR, nullptr};
+
+static const ParamMapping paramNorthPoleGridLongitudeNetCDF = {
+    PROJ_WKT2_NAME_PARAMETER_NORTH_POLE_GRID_LONGITUDE_NETCDF_CONVENTION, 0,
+    nullptr, common::UnitOfMeasure::Type::ANGULAR, nullptr};
+
+static const ParamMapping *const paramsPoleRotationNetCDFCFConvention[] = {
+    &paramGridNorthPoleLatitudeNetCDF, &paramGridNorthPoleLongitudeNetCDF,
+    &paramNorthPoleGridLongitudeNetCDF, nullptr};
+
 static const MethodMapping otherMethodMappings[] = {
     {EPSG_NAME_METHOD_CHANGE_VERTICAL_UNIT,
      EPSG_CODE_METHOD_CHANGE_VERTICAL_UNIT, nullptr, nullptr, nullptr,
@@ -1333,6 +1349,9 @@ static const MethodMapping otherMethodMappings[] = {
     {PROJ_WKT2_NAME_METHOD_POLE_ROTATION_GRIB_CONVENTION, 0, nullptr, nullptr,
      nullptr, paramsPoleRotationGRIBConvention},
 
+    {PROJ_WKT2_NAME_METHOD_POLE_ROTATION_NETCDF_CF_CONVENTION, 0, nullptr,
+     nullptr, nullptr, paramsPoleRotationNetCDFCFConvention},
+
     {EPSG_NAME_METHOD_GEOCENTRIC_TRANSLATION_GEOCENTRIC,
      EPSG_CODE_METHOD_GEOCENTRIC_TRANSLATION_GEOCENTRIC, nullptr, nullptr,
      nullptr, paramsHelmert3},
diff --git a/src/proj_constants.h b/src/proj_constants.h
index 7c6d018a..f67a0583 100644
--- a/src/proj_constants.h
+++ b/src/proj_constants.h
@@ -240,6 +240,8 @@
 
 #define PROJ_WKT2_NAME_METHOD_POLE_ROTATION_GRIB_CONVENTION "Pole rotation (GRIB convention)"
 
+#define PROJ_WKT2_NAME_METHOD_POLE_ROTATION_NETCDF_CF_CONVENTION "Pole rotation (netCDF CF convention)"
+
 #define EPSG_CODE_METHOD_COLOMBIA_URBAN 1052
 #define EPSG_NAME_METHOD_COLOMBIA_URBAN "Colombia Urban"
 
@@ -514,6 +516,15 @@
 #define PROJ_WKT2_NAME_PARAMETER_AXIS_ROTATION_GRIB_CONVENTION \
     "Axis rotation (GRIB convention)"
 
+#define PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LATITUDE_NETCDF_CONVENTION \
+    "Grid north pole latitude (netCDF CF convention)"
+
+#define PROJ_WKT2_NAME_PARAMETER_GRID_NORTH_POLE_LONGITUDE_NETCDF_CONVENTION \
+    "Grid north pole longitude (netCDF CF convention)"
+
+#define PROJ_WKT2_NAME_PARAMETER_NORTH_POLE_GRID_LONGITUDE_NETCDF_CONVENTION \
+    "North pole grid longitude (netCDF CF convention)"
+
 /* ------------------------------------------------------------------------ */
 
 #define EPSG_CODE_METHOD_NTV1 9614
diff --git a/src/proj_experimental.h b/src/proj_experimental.h
index 05e49451..41865f14 100644
--- a/src/proj_experimental.h
+++ b/src/proj_experimental.h
@@ -964,6 +964,14 @@ PJ PROJ_DLL *proj_create_conversion_pole_rotation_grib_convention(
     double axis_rotation,
     const char* ang_unit_name, double ang_unit_conv_factor);
 
+PJ PROJ_DLL *proj_create_conversion_pole_rotation_netcdf_cf_convention(
+    PJ_CONTEXT *ctx,
+    double grid_north_pole_latitude,
+    double grid_north_pole_longitude,
+    double north_pole_grid_longitude,
+    const char *ang_unit_name,
+    double ang_unit_conv_factor);
+
 /* END: Generated by scripts/create_c_api_projections.py*/
 
 /**@}*/
diff --git a/test/unit/test_c_api.cpp b/test/unit/test_c_api.cpp
index 2a82af64..44dceb97 100644
--- a/test/unit/test_c_api.cpp
+++ b/test/unit/test_c_api.cpp
@@ -2805,7 +2805,13 @@ TEST_F(CApi, proj_create_projections) {
         ObjectKeeper keeper_projCRS(projCRS);
         ASSERT_NE(projCRS, nullptr);
     }
-
+    {
+        auto projCRS =
+            proj_create_conversion_pole_rotation_netcdf_cf_convention(
+                m_ctxt, 0, 0, 0, "Degree", 0.0174532925199433);
+        ObjectKeeper keeper_projCRS(projCRS);
+        ASSERT_NE(projCRS, nullptr);
+    }
     /* END: Generated by scripts/create_c_api_projections.py*/
 }
 
@@ -5199,6 +5205,71 @@ TEST_F(CApi, proj_create_derived_geographic_crs) {
 
 // ---------------------------------------------------------------------------
 
+TEST_F(CApi, proj_create_derived_geographic_crs_netcdf_cf) {
+
+    PJ *crs_4019 = proj_create(m_ctxt, "EPSG:4019");
+    ObjectKeeper keeper_crs_4019(crs_4019);
+    ASSERT_NE(crs_4019, nullptr);
+
+    PJ *conversion = proj_create_conversion_pole_rotation_netcdf_cf_convention(
+        m_ctxt, 2, 3, 4, "Degree", 0.0174532925199433);
+    ObjectKeeper keeper_conversion(conversion);
+    ASSERT_NE(conversion, nullptr);
+
+    PJ *cs = proj_crs_get_coordinate_system(m_ctxt, crs_4019);
+    ObjectKeeper keeper_cs(cs);
+    ASSERT_NE(cs, nullptr);
+
+    PJ *derived_crs = proj_create_derived_geographic_crs(
+        m_ctxt, "my rotated CRS", crs_4019, conversion, cs);
+    ObjectKeeper keeper_derived_crs(derived_crs);
+    ASSERT_NE(derived_crs, nullptr);
+
+    auto wkt = proj_as_wkt(m_ctxt, derived_crs, PJ_WKT2_2019, nullptr);
+    const char *expected_wkt =
+        "GEOGCRS[\"my rotated CRS\",\n"
+        "    BASEGEOGCRS[\"Unknown datum based upon the GRS 1980 ellipsoid\",\n"
+        "        DATUM[\"Not specified (based on GRS 1980 ellipsoid)\",\n"
+        "            ELLIPSOID[\"GRS 1980\",6378137,298.257222101,\n"
+        "                LENGTHUNIT[\"metre\",1]]],\n"
+        "        PRIMEM[\"Greenwich\",0,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433]]],\n"
+        "    DERIVINGCONVERSION[\"Pole rotation (netCDF CF convention)\",\n"
+        "        METHOD[\"Pole rotation (netCDF CF convention)\"],\n"
+        "        PARAMETER[\"Grid north pole latitude (netCDF CF "
+        "convention)\",2,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433,\n"
+        "                ID[\"EPSG\",9122]]],\n"
+        "        PARAMETER[\"Grid north pole longitude (netCDF CF "
+        "convention)\",3,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433,\n"
+        "                ID[\"EPSG\",9122]]],\n"
+        "        PARAMETER[\"North pole grid longitude (netCDF CF "
+        "convention)\",4,\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433,\n"
+        "                ID[\"EPSG\",9122]]]],\n"
+        "    CS[ellipsoidal,2],\n"
+        "        AXIS[\"geodetic latitude (Lat)\",north,\n"
+        "            ORDER[1],\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433,\n"
+        "                ID[\"EPSG\",9122]]],\n"
+        "        AXIS[\"geodetic longitude (Lon)\",east,\n"
+        "            ORDER[2],\n"
+        "            ANGLEUNIT[\"degree\",0.0174532925199433,\n"
+        "                ID[\"EPSG\",9122]]]]";
+
+    ASSERT_NE(wkt, nullptr);
+    EXPECT_EQ(wkt, std::string(expected_wkt));
+
+    auto proj_5 = proj_as_proj_string(m_ctxt, derived_crs, PJ_PROJ_5, nullptr);
+    ASSERT_NE(proj_5, nullptr);
+    EXPECT_EQ(proj_5, std::string("+proj=ob_tran +o_proj=longlat +o_lon_p=4 "
+                                  "+o_lat_p=2 +lon_0=183 +ellps=GRS80 +no_defs "
+                                  "+type=crs"));
+}
+
+// ---------------------------------------------------------------------------
+
 TEST_F(CApi, proj_context_set_sqlite3_vfs_name) {
 
     PJ_CONTEXT *ctx = proj_context_create();