Remove ensure_nonstatic_links option from importers (#1682)

Signed-off-by: adenzler-nvidia <adenzler@nvidia.com>

Author: adenzler-nvidia

newton/_src/sim/builder.py

@@ -1504,8 +1504,6 @@ def add_urdf(
         force_show_colliders: bool = False,
         enable_self_collisions: bool = True,
         ignore_inertial_definitions: bool = False,
-        ensure_nonstatic_links: bool = False,
-        static_link_mass: float = 1e-2,
         joint_ordering: Literal["bfs", "dfs"] | None = "dfs",
         bodies_follow_joint_ordering: bool = True,
         collapse_fixed_joints: bool = False,
@@ -1590,8 +1588,6 @@ def add_urdf(
             force_show_colliders (bool): If True, the collision shapes are always shown, even if there are visual shapes.
             enable_self_collisions (bool): If True, self-collisions are enabled.
             ignore_inertial_definitions (bool): If True, the inertial parameters defined in the URDF are ignored and the inertia is calculated from the shape geometry.
-            ensure_nonstatic_links (bool): If True, links with zero mass are given a small mass (see `static_link_mass`) to ensure they are dynamic.
-            static_link_mass (float): The mass to assign to links with zero mass (if `ensure_nonstatic_links` is set to True).
             joint_ordering (str): The ordering of the joints in the simulation. Can be either "bfs" or "dfs" for breadth-first or depth-first search, or ``None`` to keep joints in the order in which they appear in the URDF. Default is "dfs".
             bodies_follow_joint_ordering (bool): If True, the bodies are added to the builder in the same order as the joints (parent then child body). Otherwise, bodies are added in the order they appear in the URDF. Default is True.
             collapse_fixed_joints (bool): If True, fixed joints are removed and the respective bodies are merged.
@@ -1619,8 +1615,6 @@ def add_urdf(
             force_show_colliders=force_show_colliders,
             enable_self_collisions=enable_self_collisions,
             ignore_inertial_definitions=ignore_inertial_definitions,
-            ensure_nonstatic_links=ensure_nonstatic_links,
-            static_link_mass=static_link_mass,
             joint_ordering=joint_ordering,
             bodies_follow_joint_ordering=bodies_follow_joint_ordering,
             collapse_fixed_joints=collapse_fixed_joints,
@@ -1859,8 +1853,6 @@ def add_mjcf(
         force_show_colliders: bool = False,
         enable_self_collisions: bool = True,
         ignore_inertial_definitions: bool = False,
-        ensure_nonstatic_links: bool = False,
-        static_link_mass: float = 1e-2,
         collapse_fixed_joints: bool = False,
         verbose: bool = False,
         skip_equality_constraints: bool = False,
@@ -1959,8 +1951,6 @@ def add_mjcf(
             force_show_colliders (bool): If True, the collision shapes are always shown, even if there are visual shapes.
             enable_self_collisions (bool): If True, self-collisions are enabled.
             ignore_inertial_definitions (bool): If True, the inertial parameters defined in the MJCF are ignored and the inertia is calculated from the shape geometry.
-            ensure_nonstatic_links (bool): If True, links with zero mass are given a small mass (see `static_link_mass`) to ensure they are dynamic.
-            static_link_mass (float): The mass to assign to links with zero mass (if `ensure_nonstatic_links` is set to True).
             collapse_fixed_joints (bool): If True, fixed joints are removed and the respective bodies are merged.
             verbose (bool): If True, print additional information about parsing the MJCF.
             skip_equality_constraints (bool): Whether <equality> tags should be parsed. If True, equality constraints are ignored.
@@ -2001,8 +1991,6 @@ def add_mjcf(
             force_show_colliders=force_show_colliders,
             enable_self_collisions=enable_self_collisions,
             ignore_inertial_definitions=ignore_inertial_definitions,
-            ensure_nonstatic_links=ensure_nonstatic_links,
-            static_link_mass=static_link_mass,
             collapse_fixed_joints=collapse_fixed_joints,
             verbose=verbose,
             skip_equality_constraints=skip_equality_constraints,

newton/_src/utils/import_mjcf.py

@@ -155,8 +155,6 @@ def parse_mjcf(
     force_show_colliders: bool = False,
     enable_self_collisions: bool = True,
     ignore_inertial_definitions: bool = False,
-    ensure_nonstatic_links: bool = False,
-    static_link_mass: float = 1e-2,
     collapse_fixed_joints: bool = False,
     verbose: bool = False,
     skip_equality_constraints: bool = False,
@@ -256,8 +254,6 @@ def parse_mjcf(
         force_show_colliders (bool): If True, the collision shapes are always shown, even if there are visual shapes.
         enable_self_collisions (bool): If True, self-collisions are enabled.
         ignore_inertial_definitions (bool): If True, the inertial parameters defined in the MJCF are ignored and the inertia is calculated from the shape geometry.
-        ensure_nonstatic_links (bool): If True, links with zero mass are given a small mass (see `static_link_mass`) to ensure they are dynamic.
-        static_link_mass (float): The mass to assign to links with zero mass (if `ensure_nonstatic_links` is set to True).
         collapse_fixed_joints (bool): If True, fixed joints are removed and the respective bodies are merged.
         verbose (bool): If True, print additional information about parsing the MJCF.
         skip_equality_constraints (bool): Whether <equality> tags should be parsed. If True, equality constraints are ignored.
@@ -1455,16 +1451,6 @@ def parse_body(
                 builder.body_inv_inertia[link] = wp.inverse(I_m)
             else:
                 builder.body_inv_inertia[link] = I_m
-        if m == 0.0 and ensure_nonstatic_links:
-            # set the mass to something nonzero to ensure the body is dynamic
-            m = static_link_mass
-            # cube with side length 0.5
-            I_m = wp.mat33(np.eye(3)) * m / 12.0 * (0.5 * scale) ** 2 * 2.0
-            I_m += wp.mat33(builder.default_body_armature * np.eye(3))
-            builder.body_mass[link] = m
-            builder.body_inv_mass[link] = 1.0 / m
-            builder.body_inertia[link] = I_m
-            builder.body_inv_inertia[link] = wp.inverse(I_m)
 
         # -----------------
         # recurse

newton/_src/utils/import_urdf.py

@@ -80,8 +80,6 @@ def parse_urdf(
     force_show_colliders: bool = False,
     enable_self_collisions: bool = True,
     ignore_inertial_definitions: bool = False,
-    ensure_nonstatic_links: bool = False,
-    static_link_mass: float = 1e-2,
     joint_ordering: Literal["bfs", "dfs"] | None = "dfs",
     bodies_follow_joint_ordering: bool = True,
     collapse_fixed_joints: bool = False,
@@ -167,8 +165,6 @@ def parse_urdf(
         force_show_colliders (bool): If True, the collision shapes are always shown, even if there are visual shapes.
         enable_self_collisions (bool): If True, self-collisions are enabled.
         ignore_inertial_definitions (bool): If True, the inertial parameters defined in the URDF are ignored and the inertia is calculated from the shape geometry.
-        ensure_nonstatic_links (bool): If True, links with zero mass are given a small mass (see `static_link_mass`) to ensure they are dynamic.
-        static_link_mass (float): The mass to assign to links with zero mass (if `ensure_nonstatic_links` is set to True).
         joint_ordering (str): The ordering of the joints in the simulation. Can be either "bfs" or "dfs" for breadth-first or depth-first search, or ``None`` to keep joints in the order in which they appear in the URDF. Default is "dfs".
         bodies_follow_joint_ordering (bool): If True, the bodies are added to the builder in the same order as the joints (parent then child body). Otherwise, bodies are added in the order they appear in the URDF. Default is True.
         collapse_fixed_joints (bool): If True, fixed joints are removed and the respective bodies are merged.
@@ -651,16 +647,6 @@ def parse_shapes(link: int, geoms, density, incoming_xform=None, visible=True, j
                 m = float(el_mass.get("value", 0))
                 builder.body_mass[link] = m
                 builder.body_inv_mass[link] = 1.0 / m if m > 0.0 else 0.0
-        if m == 0.0 and ensure_nonstatic_links:
-            # set the mass to something nonzero to ensure the body is dynamic
-            m = static_link_mass
-            # cube with side length 0.5
-            I_m = wp.mat33(np.eye(3)) * m / 12.0 * (0.5 * scale) ** 2 * 2.0
-            I_m += wp.mat33(builder.default_body_armature * np.eye(3))
-            builder.body_mass[link] = m
-            builder.body_inv_mass[link] = 1.0 / m
-            builder.body_inertia[link] = I_m
-            builder.body_inv_inertia[link] = wp.inverse(I_m)
 
     end_shape_count = len(builder.shape_type)
 

newton/tests/test_import_mjcf.py

@@ -6125,15 +6125,14 @@ def test_frictionloss_from_default_class(self):
 
 
 class TestZeroMassBodies(unittest.TestCase):
-    """Verify that ``ensure_nonstatic_links`` correctly handles zero-mass bodies.
+    """Verify that zero-mass bodies are preserved as-is during import.
 
     Models may contain zero-mass bodies (sensor frames, reference links).
-    These tests ensure the default (False) preserves zero mass and that
-    opting in (True) assigns a small surrogate mass.
+    These should keep their zero mass after import.
     """
 
-    def test_ensure_nonstatic_links_default_false(self):
-        """Verify zero-mass bodies keep zero mass with the default setting."""
+    def test_zero_mass_body_preserved(self):
+        """Verify zero-mass bodies keep zero mass after import."""
         mjcf = """
         <mujoco>
             <worldbody>
@@ -6150,22 +6149,3 @@ def test_ensure_nonstatic_links_default_false(self):
 
         empty_idx = next(i for i in range(builder.body_count) if builder.body_key[i] == "empty_body")
         self.assertEqual(builder.body_mass[empty_idx], 0.0)
-
-    def test_ensure_nonstatic_links_opt_in(self):
-        """Verify zero-mass bodies receive surrogate mass when opted in."""
-        mjcf = """
-        <mujoco>
-            <worldbody>
-                <body name="robot" pos="0 0 1">
-                    <freejoint name="root"/>
-                    <inertial pos="0 0 0" mass="1.0" diaginertia="0.01 0.01 0.01"/>
-                </body>
-                <body name="empty_body" pos="0.5 0 0"/>
-            </worldbody>
-        </mujoco>
-        """
-        builder = newton.ModelBuilder()
-        builder.add_mjcf(mjcf, ensure_nonstatic_links=True)
-
-        empty_idx = next(i for i in range(builder.body_count) if builder.body_key[i] == "empty_body")
-        self.assertGreater(builder.body_mass[empty_idx], 0.0)

newton/tests/test_import_urdf.py

@@ -1595,7 +1595,7 @@ def add_link(self, *args, key=None, **kwargs):
 
         builder = _SkippingLinkBuilder()
         with self.assertWarnsRegex(UserWarning, "was not created, skipping mimic constraint"):
-            builder.add_urdf(urdf, joint_ordering=None, ensure_nonstatic_links=False)
+            builder.add_urdf(urdf, joint_ordering=None)
 
         # No mimic constraint should be created because the follower joint was skipped.
         self.assertEqual(len(builder.constraint_mimic_joint0), 0)

newton/tests/test_mujoco_solver.py

@@ -6087,8 +6087,8 @@ class TestMuJoCoSolverZeroMassBody(unittest.TestCase):
     def test_zero_mass_body(self):
         """SolverMuJoCo accepts models with zero-mass bodies (e.g. sensor frames).
 
-        With ensure_nonstatic_links=False (the default), zero-mass bodies keep
-        their zero mass. MuJoCo handles these natively when they have fixed joints.
+        Zero-mass bodies keep their zero mass. MuJoCo handles these natively
+        when they have fixed joints.
         """
         mjcf = """
         <mujoco>