Support passing a subset of links to be parametrized

src/jaxsim/api/model.py

@@ -141,6 +141,7 @@ def build_from_model_description(
         considered_joints: Sequence[str] | None = None,
         gravity: jtp.FloatLike = jaxsim.math.STANDARD_GRAVITY,
         constraints: jaxsim.rbda.kinematic_constraints.ConstraintMap | None = None,
+        parametrized_links: tuple[str, ...] | None = None,
     ) -> JaxSimModel:
         """
         Build a Model object from a model description.
@@ -170,6 +171,8 @@ def build_from_model_description(
             constraints:
                 An object of type ConstraintMap containing the kinematic constraints to consider. If None, no constraints are considered.
                 Note that constraints can be used only with RelaxedRigidContacts.
+            parametrized_links:
+                The optional list of links to be parametrized. If None, all links are parametrized.
 
         Returns:
             The built Model object.
@@ -202,6 +205,7 @@ def build_from_model_description(
             integrator=integrator,
             gravity=-gravity,
             constraints=constraints,
+            parametrized_links=parametrized_links,
         )
 
         # Store the origin of the model, in case downstream logic needs it.
@@ -212,7 +216,9 @@ def build_from_model_description(
         # TODO: move the building of the metadata to KinDynParameters.build()
         #       and use the model_description instead of model.built_from.
         with model.mutable_context(mutability=Mutability.MUTABLE_NO_VALIDATION):
-            model.kin_dyn_parameters.hw_link_metadata = model.compute_hw_link_metadata()
+            model.kin_dyn_parameters.hw_link_metadata = model.compute_hw_link_metadata(
+                parametrized_links=parametrized_links
+            )
 
         return model
 
@@ -230,6 +236,7 @@ def build(
         integrator: IntegratorType | None = None,
         gravity: jtp.FloatLike = jaxsim.math.STANDARD_GRAVITY,
         constraints: jaxsim.rbda.kinematic_constraints.ConstraintMap | None = None,
+        parametrized_links: tuple[str, ...] | None = None,
     ) -> JaxSimModel:
         """
         Build a Model object from an intermediate model description.
@@ -254,6 +261,8 @@ def build(
             gravity: The gravity constant.
             constraints:
                 An object of type ConstraintMap containing the kinematic constraints to consider. If None, no constraints are considered.
+            parametrized_links:
+                The optional list of links to be parametrized. If None, all links are parametrized.
 
         Returns:
             The built Model object.
@@ -320,10 +329,17 @@ def build(
 
         return model
 
-    def compute_hw_link_metadata(self) -> HwLinkMetadata:
+    def compute_hw_link_metadata(
+        self, parametrized_links: tuple[str, ...] | None = None
+    ) -> HwLinkMetadata:
         """
         Compute the parametric metadata of the links in the model.
 
+        Args:
+            parametrized_links:
+                An optional tuple of link names to be parametrized. If None,
+                all links will be parametrized.
+
         Returns:
             An instance of HwLinkMetadata containing the metadata of all links.
         """
@@ -370,19 +386,20 @@ def compute_hw_link_metadata(self) -> HwLinkMetadata:
         L_H_pre_masks = []
         L_H_pre = []
 
-        # Process each link
+        # Process each link, only parametrizing those in parametrized_links if provided
         for link_description in ordered_links:
             link_name = link_description.name
 
-            if link_name not in self.link_names():
-                logging.debug(
-                    f"Skipping link '{link_name}' for hardware parametrization as it is not part of the JaxSim model."
-                )
-
-            if link_name not in rod_links_dict:
-                logging.debug(
-                    f"Skipping link '{link_name}' for hardware parametrization as it is not part of the ROD model."
-                )
+            if parametrized_links is not None and link_name not in parametrized_links:
+                # Mark as unsupported for non-parametrized links
+                shapes.append(LinkParametrizableShape.Unsupported)
+                geoms.append([0, 0, 0])
+                densities.append(0.0)
+                L_H_Gs.append(jnp.eye(4))
+                L_H_vises.append(jnp.eye(4))
+                L_H_pre_masks.append([0] * self.number_of_joints())
+                L_H_pre.append([jnp.eye(4)] * self.number_of_joints())
+                continue
 
             rod_link = rod_links_dict.get(link_name)
             link_index = int(js.link.name_to_idx(model=self, link_name=link_name))

tests/test_api_model_hw_parametrization.py

@@ -656,6 +656,27 @@ def test_unsupported_link_cases():
         err_msg="Sphere radius must match the first visual",
     )
 
+    # Test selective parametrization: only 'supported_link' and 'double_visual_link' should be parametrized
+    selective_model = js.model.JaxSimModel.build_from_model_description(
+        multi_link_urdf, is_urdf=True, parametrized_links=("double_visual_link")
+    )
+    selective_metadata = selective_model.kin_dyn_parameters.hw_link_metadata
+
+    # Check that only the selected links are parametrized
+    link_indices = {name: idx for idx, name in enumerate(selective_model.link_names())}
+    assert (
+        selective_metadata.link_shape[link_indices["supported_link"]]
+        == LinkParametrizableShape.Unsupported
+    ), "Selected supported_link should be parametrized as Box"
+    assert (
+        selective_metadata.link_shape[link_indices["double_visual_link"]]
+        == LinkParametrizableShape.Sphere
+    ), "Selected double_visual_link should be parametrized as Sphere"
+    assert (
+        selective_metadata.link_shape[link_indices["unsupported_link"]]
+        == LinkParametrizableShape.Unsupported
+    ), "Non-selected unsupported_link should be marked as Unsupported"
+
 
 def test_export_continuous_joint_handling():
     """