Do not filter links that have children.

src/adam/model/std_factories/std_model.py

@@ -37,16 +37,8 @@ def __init__(self, path: str, math: SpatialMath):
         if not path.exists():
             raise FileExistsError(path)
 
-        # Read URDF, but before passing it to urdf_parser_py get rid of all sensor tags
-        # sensor tags are valid elements of URDF (see ),
-        # but they are ignored by urdf_parser_py, that complains every time it sees one.
-        # As there is nothing to be fixed in the used models, and it is not useful
-        # to have a useless and noisy warning, let's remove before hands all the sensor elements,
-        # that anyhow are not parser by urdf_parser_py or adam
-        # See https://github.com/ami-iit/ADAM/issues/59
-        xml_file = open(path, "r")
-        xml_string = xml_file.read()
-        xml_file.close()
+        with open(path, "r") as xml_file:
+            xml_string = xml_file.read()
         xml_string_without_sensors_tags = urdf_remove_sensors_tags(xml_string)
         self.urdf_desc = urdf_parser_py.urdf.URDF.from_xml_string(
             xml_string_without_sensors_tags
@@ -66,15 +58,21 @@ def get_links(self) -> List[StdLink]:
             List[StdLink]: build the list of the links
         """
         return [
-            self.build_link(l) for l in self.urdf_desc.links if l.inertial is not None
+            self.build_link(l)
+            for l in self.urdf_desc.links
+            if (l.inertial is not None or l.name in self.urdf_desc.child_map.keys())
         ]
 
     def get_frames(self) -> List[StdLink]:
         """
         Returns:
             List[StdLink]: build the list of the links
         """
-        return [self.build_link(l) for l in self.urdf_desc.links if l.inertial is None]
+        return [
+            self.build_link(l)
+            for l in self.urdf_desc.links
+            if l.inertial is None and l.name not in self.urdf_desc.child_map.keys()
+        ]
 
     def build_joint(self, joint: urdf_parser_py.urdf.Joint) -> StdJoint:
         """