Add support for separate collision mesh format in convert-urdf-mesh (#593)

This change allows different mesh formats for visual and collision
geometries in URDF files. Collision meshes now default to STL format
for better compatibility with physics engines, while visual meshes
remain as DAE to preserve colors and textures.

Key changes:
- Add --collision-mesh-format option (default: stl)
- Implement context tracking to distinguish visual/collision meshes
- Update mesh conversion logic to handle formats independently

Author: iory

skrobot/apps/convert_urdf_mesh.py

@@ -28,7 +28,11 @@ def main():
     parser.add_argument('--format', '-f',
                         default='dae',
                         choices=['dae', 'stl'],
-                        help='Mesh format for export. Default is dae.')
+                        help='Mesh format for visual mesh export. Default is dae.')
+    parser.add_argument('--collision-mesh-format',
+                        default='stl',
+                        choices=['dae', 'stl'],
+                        help='Mesh format for collision mesh export. Default is stl.')
     parser.add_argument('--output', '-o', help='Path for the output URDF file. If not specified, a filename is automatically generated based on the input URDF file.')  # NOQA
     parser.add_argument('--inplace', '-i', action='store_true',
                         help='Modify the input URDF file inplace. If not specified, a new file is created.')  # NOQA
@@ -133,7 +137,8 @@ def nullcontext(enter_result=None):
             decimation_area_ratio_threshold=args.decimation_area_ratio_threshold,  # NOQA
             simplify_vertex_clustering_voxel_size=args.voxel_size,
             target_triangles=args.target_triangles,
-            overwrite_mesh=args.overwrite_mesh), apply_scale(args.scale):
+            overwrite_mesh=args.overwrite_mesh,
+            collision_mesh_format='.' + args.collision_mesh_format), apply_scale(args.scale):
         print(f"Saving new URDF to: {output_path}")
         # Ensure output directory exists
         output_dir = output_path.parent

skrobot/utils/urdf.py

@@ -43,13 +43,15 @@
 _CONFIGURABLE_VALUES = {"mesh_simplify_factor": np.inf,
                         'no_mesh_load_mode': False,
                         'export_mesh_format': None,
+                        'collision_mesh_format': None,
                         'decimation_area_ratio_threshold': None,
                         'simplify_vertex_clustering_voxel_size': None,
                         'target_triangles': None,
                         'enable_mesh_cache': False,
                         'force_visual_mesh_origin_to_zero': False,
                         'overwrite_mesh': False,
                         'scale_factor': 1.0,
+                        '_current_geometry_context': None,  # 'collision' or 'visual'
                         }
 _MESH_CACHE = {}
 
@@ -74,8 +76,10 @@ def export_mesh_format(
         decimation_area_ratio_threshold=None,
         simplify_vertex_clustering_voxel_size=None,
         target_triangles=None,
-        overwrite_mesh=False):
+        overwrite_mesh=False,
+        collision_mesh_format=None):
     _CONFIGURABLE_VALUES["export_mesh_format"] = mesh_format
+    _CONFIGURABLE_VALUES["collision_mesh_format"] = collision_mesh_format
     _CONFIGURABLE_VALUES["decimation_area_ratio_threshold"] = \
         decimation_area_ratio_threshold
     _CONFIGURABLE_VALUES["simplify_vertex_clustering_voxel_size"] = \
@@ -84,6 +88,7 @@ def export_mesh_format(
     _CONFIGURABLE_VALUES["overwrite_mesh"] = overwrite_mesh
     yield
     _CONFIGURABLE_VALUES["export_mesh_format"] = None
+    _CONFIGURABLE_VALUES["collision_mesh_format"] = None
     _CONFIGURABLE_VALUES["decimation_area_ratio_threshold"] = None
     _CONFIGURABLE_VALUES["simplify_vertex_clustering_voxel_size"] = None
     _CONFIGURABLE_VALUES["target_triangles"] = None
@@ -1009,11 +1014,16 @@ def _to_xml(self, parent, path):
 
             return node
 
-        ext = _CONFIGURABLE_VALUES['export_mesh_format']
+        # Determine which format to use based on context
+        is_collision = (_CONFIGURABLE_VALUES.get('_current_geometry_context')
+                        == 'collision')
+        ext = (_CONFIGURABLE_VALUES['collision_mesh_format'] if is_collision
+               else _CONFIGURABLE_VALUES['export_mesh_format'])
+
         if ext is not None:
             if not fn.endswith(ext):
                 name, _ = os.path.splitext(fn)
-                fn = name + _CONFIGURABLE_VALUES['export_mesh_format']
+                fn = name + ext
                 self.filename = os.path.splitext(self.filename)[0] + ext
                 if os.path.exists(fn):
                     # skip mesh save process but still apply scaling
@@ -1481,16 +1491,21 @@ def _from_xml(cls, node, path):
         return Collision(**kwargs)
 
     def _to_xml(self, parent, path):
-        node = self._unparse(path)
+        # Set context for mesh conversion
+        _CONFIGURABLE_VALUES['_current_geometry_context'] = 'collision'
+        try:
+            node = self._unparse(path)
 
-        # Apply scale factor to collision origin
-        scaled_origin = self.origin.copy()
-        scale_factor = _CONFIGURABLE_VALUES.get('scale_factor', 1.0)
-        if scale_factor != 1.0:
-            scaled_origin[:3, 3] *= scale_factor
+            # Apply scale factor to collision origin
+            scaled_origin = self.origin.copy()
+            scale_factor = _CONFIGURABLE_VALUES.get('scale_factor', 1.0)
+            if scale_factor != 1.0:
+                scaled_origin[:3, 3] *= scale_factor
 
-        node.append(unparse_origin(scaled_origin))
-        return node
+            node.append(unparse_origin(scaled_origin))
+            return node
+        finally:
+            _CONFIGURABLE_VALUES['_current_geometry_context'] = None
 
 
 class Visual(URDFType):
@@ -1595,16 +1610,21 @@ def _from_xml(cls, node, path):
         return Visual(**kwargs)
 
     def _to_xml(self, parent, path):
-        node = self._unparse(path)
+        # Set context for mesh conversion
+        _CONFIGURABLE_VALUES['_current_geometry_context'] = 'visual'
+        try:
+            node = self._unparse(path)
 
-        # Apply scale factor to visual origin
-        scaled_origin = self.origin.copy()
-        scale_factor = _CONFIGURABLE_VALUES.get('scale_factor', 1.0)
-        if scale_factor != 1.0:
-            scaled_origin[:3, 3] *= scale_factor
+            # Apply scale factor to visual origin
+            scaled_origin = self.origin.copy()
+            scale_factor = _CONFIGURABLE_VALUES.get('scale_factor', 1.0)
+            if scale_factor != 1.0:
+                scaled_origin[:3, 3] *= scale_factor
 
-        node.append(unparse_origin(scaled_origin))
-        return node
+            node.append(unparse_origin(scaled_origin))
+            return node
+        finally:
+            _CONFIGURABLE_VALUES['_current_geometry_context'] = None
 
 
 class Inertial(URDFType):