Add cell center automatically in VTK outputs

This is useful/necessary to define properly cuts

src/output/VTKWriter.cpp

@@ -2,6 +2,8 @@
 
 #include <mesh/Connectivity.hpp>
 #include <mesh/Mesh.hpp>
+#include <mesh/MeshData.hpp>
+#include <mesh/MeshDataManager.hpp>
 #include <utils/Messenger.hpp>
 #include <utils/RevisionInfo.hpp>
 
@@ -279,6 +281,7 @@ VTKWriter::_write(const std::shared_ptr<const MeshType>& mesh,
   // Adding basic mesh information
   output_named_item_value_set.add(NamedItemValue{"cell_number", mesh->connectivity().cellNumber()});
   output_named_item_value_set.add(NamedItemValue{"node_number", mesh->connectivity().nodeNumber()});
+  output_named_item_value_set.add(NamedItemValue{"cell_center", MeshDataManager::instance().getMeshData(*mesh).xj()});
 
   if (parallel::rank() == 0) {   // write PVTK file
     std::ofstream fout(_getFilenamePVTU());