FEM: Fenics mesh issue #0003038: xml import fixed

src/Mod/Fem/feminout/importFenicsMesh.py

@@ -150,6 +150,9 @@ def export(objectslist, fileString):
     if fileString != "":
         fileName, fileExtension = os.path.splitext(fileString)
         if fileExtension.lower() == '.xml':
+            FreeCAD.Console.PrintWarning("XML is not designed to save higher order elements.\n")
+            FreeCAD.Console.PrintWarning("Reducing order for second order mesh.\n")            
+            FreeCAD.Console.PrintWarning("Tri6 -> Tri3, Tet10 -> Tet4, etc.\n")            
             writeFenicsXML.write_fenics_mesh_xml(obj, fileString)
         elif fileExtension.lower() == '.xdmf':
             if importToolsFem.get_FemMeshObjectMeshGroups(obj) is not ():

src/Mod/Fem/feminout/readFenicsXML.py

@@ -61,6 +61,8 @@ def read_fenics_mesh_xml(xmlfilename):
         print("Mesh dimension: %d" % (dim,))
         print("Mesh cell type: %s" % (cell_type,))
 
+        # every cell type contains a dict with key=dimension and value=number
+
         cells_parts_dim = {'point': {0: 1},
                            'interval': {0: 2, 1: 1},
                            'triangle': {0: 3, 1: 3, 2: 1},
@@ -178,6 +180,10 @@ def read_fenics_mesh_xml(xmlfilename):
                            'hexahedron': ['quadrilateral', 'interval'],
                            'quadrilateral': ['interval']}
 
+        # generate cell list from file
+        # read vertex list from cells
+        # generate lower dimensional objects in mesh from cell
+
         for (cell_index, cell) in list(cell_dict.items()):
             cell_lower_dims = lower_dims_dict[cell_type]
             element_counter[cell_type] += 1
@@ -189,18 +195,25 @@ def read_fenics_mesh_xml(xmlfilename):
                         vertextuple,
                         element_counter[ld])
 
-        length_counter = len(nodes)
+        length_counter = len(nodes)  # maintain distinct counting values
+        # print("nodes")
+        # print("len & len counter", length_counter)
         for (key, val_dict) in list(element_dict.items()):
             # to ensure distinct indices for FreeCAD
+            # print('key: ', key)
             for (vkey, it) in list(val_dict.items()):
-                val_dict[vkey] = it + length_counter
-            length_counter += len(val_dict)
+                val_dict[vkey] = it + length_counter  # maintain distinct element numbers
+            len_val_dict = len(val_dict)
+            if len_val_dict > 0:
+                length_counter += len_val_dict + 1  # only if preceeding list is not empty
+            # print('len: ', len_val_dict)
+            # print('lencounter: ', length_counter)
             # inverse of the dict (dict[key] = val -> dict[val] = key)
             element_dict[key] = invertdict(val_dict)
 
-        correct_volume_det(element_dict)
+        correct_volume_det(element_dict)  # corrects negative determinants
 
-        return element_dict
+        return element_dict  # returns complete element dictionary
 
     nodes = {}
     element_dict = {}
@@ -219,6 +232,11 @@ def read_fenics_mesh_xml(xmlfilename):
         print("Mesh found")
         (nodes, cells_dict, cell_type, dim) = read_mesh_block(find_mesh)
         element_dict = generate_lower_dimensional_structures(nodes, cells_dict, cell_type, dim)
+        print("Show min max element dict")        
+        for (elm, numbers) in list(element_dict.items()):
+            lst = sorted(list(numbers.items()), key=lambda x: x[0])
+            if lst != []:
+                print(elm, " min: ", lst[0], " max: ", lst[-1])
     else:
         print("No mesh found")
 

src/Mod/Fem/feminout/writeFenicsXML.py

@@ -40,7 +40,9 @@ def write_fenics_mesh_xml(fem_mesh_obj, outputfile):
         vertices to be exported. (For second order elements, we have to delete the mid element nodes.)
     """
 
-    # TODO: check for second order elements (what to do? deny export or reduce element order?)
+    # TODO: check for second order elements 
+    # (reduce element order would be ok - all elements have at least the first
+    # necessary nodes)
 
     FreeCAD_to_Fenics_dict = {
         "Triangle": "triangle",
@@ -53,6 +55,15 @@ def write_fenics_mesh_xml(fem_mesh_obj, outputfile):
         "Polygon": "unknown", "Polyhedron": "unknown",
         "Prism": "unknown", "Pyramid": "unknown",
     }
+    
+    XML_Number_of_Nodes_dict = {
+        "point": 1,
+        "interval": 2,
+        "triangle": 3,
+        "quadrilateral": 4,
+        "tetrahedron": 4,
+        "hexahedron": 8
+    }
 
     print("Converting " + fem_mesh_obj.Label + " to fenics XML File")
     print("Dimension of mesh: %d" % (get_FemMeshObjectDimension(fem_mesh_obj),))
@@ -62,6 +73,7 @@ def write_fenics_mesh_xml(fem_mesh_obj, outputfile):
     celltype_in_mesh = get_MaxDimElementFromList(elements_in_mesh)
     (num_cells, cellname_fc, dim_cell) = celltype_in_mesh
     cellname_fenics = FreeCAD_to_Fenics_dict[cellname_fc]
+    num_verts_cell = XML_Number_of_Nodes_dict[cellname_fenics]
     print("Celltype in mesh -> %s and its Fenics name: %s" % (str(celltype_in_mesh), cellname_fenics))
 
     root = ET.Element("dolfin", dolfin="http://fenicsproject.org")
@@ -90,7 +102,8 @@ def write_fenics_mesh_xml(fem_mesh_obj, outputfile):
 
         cell_args = {}
         for (vi, ni) in enumerate(nodeindices):
-            cell_args["v" + str(vi)] = str(ni - 1)
+            if vi < num_verts_cell:  # XML only supports first order meshs 
+                cell_args["v" + str(vi)] = str(ni - 1)
         # generate as many v entries in dict as nodes are listed in cell (works only for first order elements)
 
         ET.SubElement(cells, cellname_fenics, index=str(fen_ind), **cell_args)