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Deltares · Sep 15, 2023 · cfd304e · cfd304e
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Showing 3 changed files with 37 additions and 4 deletions.
diff --git a/include/UGrid/UGridEntity.hpp b/include/UGrid/UGridEntity.hpp
@@ -137,6 +137,30 @@ namespace ugrid
         /// @return The variables names
         [[nodiscard]] std::vector<std::string> get_data_variables_names(std::string const& location_string);
 
+        /// @brief This function adjusts the values in an input array based on the difference between the provided `start_index`
+        /// and the `start_index` stored in the specified NetCDF variable's attribute named "start_index". If the attribute is not found, no adjustments are made to the array.
+        /// @tparam T The data type of the input array `values`.
+        /// @param[in] var The NetCDF variable from which to retrieve the "start_index" attribute.
+        /// @param[in] start_index The desired start index for the array.
+        /// @param[in] values_size The size of the input array `values`.
+        /// @param[in,out] values The input array to which the offset is applied.
+        template <typename T>
+        static void apply_start_index_offset(const netCDF::NcVar& var, int start_index, int values_size, T* values)
+        {
+            const auto varAtt = var.getAtts();
+            std::string start_index_att_name{"start_index"};
+            if (varAtt.find(start_index_att_name) != varAtt.end())
+            {
+                int variable_start_index;
+                varAtt.at(start_index_att_name).getValues(&variable_start_index);
+                int offset = start_index - variable_start_index;
+                for (auto i = 0; i < values_size; ++i)
+                {
+                    values[i] += offset;
+                }
+            }
+        }
+
     protected:
         /// @brief Method collecting common operations for defining a UGrid entity to file
         /// @param entity_name [in] The entity name

diff --git a/src/UGrid/Mesh2D.cpp b/src/UGrid/Mesh2D.cpp
@@ -295,7 +295,9 @@ void Mesh2D::get(ugridapi::Mesh2D& mesh2d) const
     // Edges
     if (auto const it = m_topology_attribute_variables.find("edge_node_connectivity"); mesh2d.edge_nodes != nullptr && it != m_topology_attribute_variables.end())
     {
-        it->second.at(0).getVar(mesh2d.edge_nodes);
+        const auto var = it->second.at(0);
+        var.getVar(mesh2d.edge_nodes);
+        apply_start_index_offset(var, mesh2d.start_index, mesh2d.num_edges, mesh2d.edge_nodes);
     }
     if (auto const it = m_topology_attribute_variables.find("edge_face_connectivity"); mesh2d.edge_faces != nullptr && it != m_topology_attribute_variables.end())
     {
@@ -313,15 +315,21 @@ void Mesh2D::get(ugridapi::Mesh2D& mesh2d) const
     // Faces
     if (auto const it = m_topology_attribute_variables.find("face_node_connectivity"); mesh2d.face_nodes != nullptr && it != m_topology_attribute_variables.end())
     {
-        it->second.at(0).getVar(mesh2d.face_nodes);
+        const auto var = it->second.at(0);
+        var.getVar(mesh2d.face_nodes);
+        apply_start_index_offset(var, mesh2d.start_index, mesh2d.num_faces * mesh2d.num_face_nodes_max, mesh2d.face_nodes);
     }
     if (auto const it = m_topology_attribute_variables.find("face_edge_connectivity"); mesh2d.face_edges != nullptr && it != m_topology_attribute_variables.end())
     {
-        it->second.at(0).getVar(mesh2d.face_edges);
+        const auto var = it->second.at(0);
+        var.getVar(mesh2d.face_edges);
+        apply_start_index_offset(var, mesh2d.start_index, mesh2d.num_faces * mesh2d.num_face_nodes_max, mesh2d.face_edges);
     }
     if (auto const it = m_topology_attribute_variables.find("face_face_connectivity"); mesh2d.face_faces != nullptr && it != m_topology_attribute_variables.end())
     {
-        it->second.at(0).getVar(mesh2d.face_faces);
+        const auto var = it->second.at(0);
+        var.getVar(mesh2d.face_faces);
+        apply_start_index_offset(var, mesh2d.start_index, mesh2d.num_faces * mesh2d.num_face_nodes_max, mesh2d.face_faces);
     }
     if (auto const it = m_topology_attribute_variables.find("face_coordinates"); mesh2d.face_x != nullptr && it != m_topology_attribute_variables.end())
     {

diff --git a/tests/api/ApiTests.cpp b/tests/api/ApiTests.cpp
@@ -127,6 +127,7 @@ TEST(ApiTest, InquireAndGet_OneMesh2D_ShouldReadMesh2d)
     mesh2d.face_y = face_y.data();
     std::vector<int> face_nodes(mesh2d.num_faces * mesh2d.num_face_nodes_max);
     mesh2d.face_nodes = face_nodes.data();
+    mesh2d.start_index = 1;
 
     // Execute
     error_code = ug_mesh2d_get(file_id, 0, mesh2d);