From 2fa3efe6fcad5fe6109b9618003f763278ff39bf Mon Sep 17 00:00:00 2001
From: Ulysse Bouchet <ulysse.bouchet@simvia.tech>
Date: Wed, 21 Jan 2026 16:37:18 +0100
Subject: [PATCH] Add 2D mesh support

---
 python/med2obj.py | 80 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 54 insertions(+), 26 deletions(-)

diff --git a/python/med2obj.py b/python/med2obj.py
index e9df35c..37e57f9 100644
--- a/python/med2obj.py
+++ b/python/med2obj.py
@@ -1,40 +1,59 @@
 # Convert a mesh stored in a .med file into a unique .obj file with multiple groups.
 # Each group in the .med file is converted into a group in the .obj file.
+# Supports both 3D meshes and 2D meshes (which are automatically converted to 3D).
 # usage: python med2obj.py -i input.med -o .cache_dir/output.obj
 
 
-
-
 import argparse
-import numpy as np
 import medcoupling as mc
 import pathlib as pl
 
+
 def parse_args():
-    parser = argparse.ArgumentParser(description="Convert a .med mesh file to a .obj file with groups.")
-    parser.add_argument("-i", "--input", type=str, required=True, help="Input .med file path.")
-    parser.add_argument("-o", "--output", type=str, required=True, help="Output .obj file path.")
+    parser = argparse.ArgumentParser(
+        description="Convert a .med mesh file to a .obj file with groups."
+    )
+    parser.add_argument(
+        "-i", "--input", type=str, required=True, help="Input .med file path."
+    )
+    parser.add_argument(
+        "-o", "--output", type=str, required=True, help="Output .obj file path."
+    )
     return parser.parse_args()
 
+
 END_CONNECTIVITY = {
-    9: 4,  ## Quadrangle 9 nodes -> Quadrangle 4 nodes 
+    9: 4,  ## Quadrangle 9 nodes -> Quadrangle 4 nodes
     8: 4,  ## Quadrangle 8 nodes  -> Quadrangle 4 nodes
     6: 3,  ## Triangle 6 nodes -> Triangle 3 nodes
-    3: 3,  ## Triangle 3 nodes 
+    3: 3,  ## Triangle 3 nodes
     4: 4,  ## Quadrangle 4 nodes
     2: 2,  ## Line 2 nodes
-    1: 1   ## Point 1 node
+    1: 1,  ## Point 1 node
 }
 
-def write_obj(med_file, skin_mesh, skin_groups, node_groups, output_path, skin_level=-1, node_level=1):
-    with open(output_path, 'w') as f:
+
+def write_obj(
+    med_file,
+    skin_mesh,
+    skin_groups,
+    node_groups,
+    output_path,
+    skin_level=-1,
+    node_level=1,
+):
+    with open(output_path, "w") as f:
         coords = skin_mesh.getCoords().toNumPyArray()
         for coord in coords:
-            f.write(f"v {coord[0]} {coord[1]} {coord[2]}\n")
+            # Ensure 2D coordinates are converted to 3D by adding z=0 if missing
+            if len(coord) == 2:
+                f.write(f"v {coord[0]} {coord[1]} 0.0\n")
+            else:
+                f.write(f"v {coord[0]} {coord[1]} {coord[2]}\n")
 
         for elem in skin_mesh:
-            conn = elem.getAllConn()# OBJ is 1-indexed
-            end_connectivity = END_CONNECTIVITY[len(conn)-1]+1
+            conn = elem.getAllConn()  # OBJ is 1-indexed
+            end_connectivity = END_CONNECTIVITY[len(conn) - 1] + 1
             f.write(f'f {" ".join([str(x+1) for x in conn[1:end_connectivity]])}\n')
 
         for group_name in skin_groups:
@@ -42,7 +61,7 @@ def write_obj(med_file, skin_mesh, skin_groups, node_groups, output_path, skin_l
             f.write(f"g {group_name}\n")
             for elem in submesh:
                 conn = elem.getAllConn()
-                end_connectivity = END_CONNECTIVITY[len(conn)-1]+1
+                end_connectivity = END_CONNECTIVITY[len(conn) - 1] + 1
                 f.write(f'f {" ".join([str(x+1) for x in conn[1:end_connectivity]])}\n')
 
         for group_name in node_groups:
@@ -51,8 +70,8 @@ def write_obj(med_file, skin_mesh, skin_groups, node_groups, output_path, skin_l
             for node_id in node_ids:
                 f.write(f"p {node_id + 1}\n")  # OBJ is 1-indexed
 
-def main():
 
+def main():
     args = parse_args()
     input_path = pl.Path(args.input)
     output_path = pl.Path(args.output)
@@ -61,23 +80,32 @@ def main():
         raise FileNotFoundError(f"Input file {input_path} does not exist.")
 
     med_file = mc.MEDFileUMesh.New(str(input_path))
-    #med_file = med_file.quadraticToLinear()
+    # med_file = med_file.quadraticToLinear()
     mesh = med_file.getMeshAtLevel(0)
 
-    node_level = 1 
-    if mesh.getMeshDimension() == 3: ## Volumic 3d mesh
+    node_level = 1
+    if mesh.getMeshDimension() == 3:  ## Volumic 3d mesh
         ## compute only the skin of the mesh
         skin_mesh = mesh.computeSkin()
         surface_level = -1
-    else:
+    elif mesh.getMeshDimension() == 2:  ## 2D mesh - convert to 3D
+        skin_mesh = mesh.clone(True)
+        surface_level = 0
+    else:  ## 1D or other - clone as is
         skin_mesh = mesh.clone(True)
         surface_level = 0
-
 
     nodes = med_file.getGroupsOnSpecifiedLev(node_level)
     surfaces = med_file.getGroupsOnSpecifiedLev(surface_level)
-    write_obj(med_file, skin_mesh, surfaces, nodes, str(output_path), skin_level=surface_level, node_level=node_level)
-
-
-
-main()
\ No newline at end of file
+    write_obj(
+        med_file,
+        skin_mesh,
+        surfaces,
+        nodes,
+        str(output_path),
+        skin_level=surface_level,
+        node_level=node_level,
+    )
+
+
+main()