Retrieve local ijk's of an LGR, given its name

CMakeLists_files.cmake

@@ -37,6 +37,7 @@ list (APPEND MAIN_SOURCE_FILES
   opm/grid/cpgrid/Iterators.cpp
   opm/grid/cpgrid/Indexsets.cpp
   opm/grid/cpgrid/PartitionTypeIndicator.cpp
+  opm/grid/cpgrid/CpGridUtilities.cpp
   opm/grid/cpgrid/processEclipseFormat.cpp
   opm/grid/common/GeometryHelpers.cpp
   opm/grid/common/GridPartitioning.cpp
@@ -115,6 +116,7 @@ if(Boost_VERSION_STRING VERSION_GREATER 1.53)
 	  tests/cpgrid/grid_lgr_test.cpp
 	  tests/cpgrid/inactiveCell_lgr_test.cpp
 	  tests/cpgrid/lgr_cartesian_idx_test.cpp
+	  tests/cpgrid/lgrIJK_test.cpp
 	  tests/cpgrid/lookUpCellCentroid_cpgrid_test.cpp
 	  tests/cpgrid/lookupdataCpGrid_test.cpp
 	  tests/cpgrid/replace_lgr1_corner_idx_by_lgr2_corner_idx_test.cpp
@@ -179,6 +181,7 @@ list (APPEND PUBLIC_HEADER_FILES
   opm/grid/cpgrid/CartesianIndexMapper.hpp
   opm/grid/cpgrid/CpGridData.hpp
   opm/grid/cpgrid/CpGridDataTraits.hpp
+  opm/grid/cpgrid/CpGridUtilities.hpp
   opm/grid/cpgrid/DataHandleWrappers.hpp
   opm/grid/cpgrid/DefaultGeometryPolicy.hpp
   opm/grid/cpgrid/dgfparser.hh

opm/grid/cpgrid/CpGridUtilities.cpp

@@ -0,0 +1,68 @@
+/*
+  Copyright 2025
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <opm/grid/cpgrid/CpGridUtilities.hpp>
+#include <opm/grid/cpgrid/LevelCartesianIndexMapper.hpp>
+
+#include <array>
+#include <string>
+#include <tuple>
+#include <unordered_map>
+#include <vector>
+
+namespace Opm
+{
+
+std::tuple<std::vector<int>, std::unordered_map<int, int>, std::vector<std::array<int, 3>>>
+lgrIJK(const Dune::CpGrid& grid, const std::string& lgr_name)
+{
+    // Check if lgr_name exists in lgr_names_
+    const auto& lgr_names = grid.getLgrNameToLevel();
+    auto it = lgr_names.find(lgr_name);
+    if (it == lgr_names.end()) {
+        OPM_THROW(std::runtime_error, "LGR name not found: " + lgr_name);
+    }
+
+    const auto level = it->second;
+    const Opm::LevelCartesianIndexMapper<Dune::CpGrid> levelCartMapper(grid);
+    const auto& levelView = grid.levelGridView(level);
+    const auto numCells = levelView.size(0);
+
+    std::vector<std::array<int, 3>> lgrIJK(numCells);
+    std::vector<int> cellIdxToLgrCartesianIdx(numCells);
+    std::unordered_map<int, int> lgrCartesianIdxToCellIdx;
+    lgrCartesianIdxToCellIdx.reserve(numCells);
+
+    // Iterate over (active) elements in the grid and populate the structures
+    for (const auto& element : Dune::elements(grid.levelGridView(level))) {
+        std::array<int, 3> ijk;
+        levelCartMapper.cartesianCoordinate(element.index(), ijk, level);
+
+        const int cellIndex = element.index();
+        const int cartesianIdx = element.getLevelCartesianIdx();
+
+        lgrIJK[cellIndex] = ijk;
+        cellIdxToLgrCartesianIdx[cellIndex] = cartesianIdx;
+        lgrCartesianIdxToCellIdx[cartesianIdx] = cellIndex;
+    }
+
+    return std::make_tuple(cellIdxToLgrCartesianIdx, lgrCartesianIdxToCellIdx, lgrIJK);
+}
+
+} // namespace Opm

opm/grid/cpgrid/CpGridUtilities.hpp

@@ -0,0 +1,44 @@
+/*
+  Copyright 2025 ....
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef OPM_CPGRIDUTILITIES_HEADER_INCLUDED
+#define OPM_CPGRIDUTILITIES_HEADER_INCLUDED
+
+#include <opm/grid/CpGrid.hpp>
+
+namespace Opm
+{
+
+/// @brief Retrieves Cartesian indices for a specified Local Grid Refinement (LGR) level in a Dune::CpGrid.
+///
+/// This function extracts the mapping between active cell indices and Cartesian indices for a given LGR name.
+/// If the specified name is not found, an exception is thrown.
+///
+/// @param grid The Dune::CpGrid
+/// @param lgr_name The name of the LGR whose indices are to be retrieved.
+/// @return A tuple containing:
+///   - A std::vector<int> mapping cell indices to their corresponding Cartesian indices in the LGR.
+///   - A std::unordered_map<int, int> mapping Cartesian indices back to cell indices (handles inactive parent cells).
+///   - A std::vector<std::array<int, 3>> storing the (i, j, k) Cartesian coordinates for active cells.
+std::tuple<std::vector<int>, std::unordered_map<int, int>, std::vector<std::array<int, 3>>>
+lgrIJK(const Dune::CpGrid& grid, const std::string& lgr_name);
+
+} // namespace Opm
+
+#endif // OPM_CPGRIDUTILITIES_HEADER_INCLUDED

opm/grid/cpgrid/Entity.hpp

@@ -607,8 +607,7 @@ template<int codim>
 int Dune::cpgrid::Entity<codim>::getLevelCartesianIdx() const
 {
     const auto& level_data = (*(pgrid_ -> level_data_ptr_))[level()].get();
-    // getLevelElem() throws when the entity does not belong to the leaf grid view.
-    return level_data -> global_cell_[getLevelElem().index()];
+    return level_data -> global_cell_[getEquivLevelElem().index()];
 }
 
 } // namespace cpgrid