Simplifies the Articulation initialization by adding some other hacks (#243)

# Description

Earlier we were copying the whole `ArticulationView.initialize()` method
from Isaac Sim since it doesn't work with our initialization callback
hooks. Since this was bulking up the code and requires us to keep
duplicating their function, this MR replaces the current fix with some
tricks that work in a less bulky way.

Additionally, the MR fixes the property name `default_root_state_w` to
`default_root_state` since the latter is more correct (environment
origin instead of world origin).

## Type of change

- Bug fix (non-breaking change which fixes an issue)
- Breaking change (fix or feature that would cause existing
functionality to not work as expected)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

source/extensions/omni.isaac.orbit/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.9.39"
+version = "0.9.40"
 
 # Description
 title = "ORBIT framework for Robot Learning"

source/extensions/omni.isaac.orbit/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.9.40 (2023-11-09)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Simplified the manual initialization of Isaac Sim :class:`ArticulationView` class. Earlier, we basically
+  copied the code from the Isaac Sim source code. Now, we just call their initialize method.
+
+Changed
+^^^^^^^
+
+* Changed the name of attribute :attr:`default_root_state_w` to :attr:`default_root_state`. The latter is
+  more correct since the data is actually in the local environment frame and not the simulation world frame.
+
+
 0.9.39 (2023-11-08)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/articulation/articulation.py

@@ -12,7 +12,6 @@ import torch
 from typing import TYPE_CHECKING, Sequence
 
 import carb
-import omni.physics.tensors
 import omni.physics.tensors.impl.api as physx
 from omni.isaac.core.articulations import ArticulationView
 from omni.isaac.core.prims import RigidPrimView
@@ -364,35 +363,18 @@ class Articulation(RigidObject):
         # -- articulation
         self._root_view = ArticulationView(self.cfg.prim_path, reset_xform_properties=False)
         # Hacking the initialization of the articulation view.
-        # we cannot do the following operation and need to manually handle it because of Isaac Sim's implementation.
-        # self._root_view.initialize()
         # reason: The default initialization of the articulation view is not working properly as it tries to create
         # default actions that is not possible within the post-play callback.
-        physics_sim_view = omni.physics.tensors.create_simulation_view(self._root_view._backend)
-        physics_sim_view.set_subspace_roots("/")
-        # pyright: ignore [reportPrivateUsage]
-        self._root_view._physics_sim_view = physics_sim_view
-        self._root_view._physics_view = physics_sim_view.create_articulation_view(
-            self._root_view._regex_prim_paths.replace(".*", "*"), self._root_view._enable_dof_force_sensors
-        )
-        assert self._root_view._physics_view.is_homogeneous, "Root view's physics view is not homogeneous!"
-        if not self._root_view._is_initialized:
-            self._root_view._metadata = self._root_view._physics_view.shared_metatype
-            self._root_view._num_dof = self._root_view._physics_view.max_dofs
-            self._root_view._num_bodies = self._root_view._physics_view.max_links
-            self._root_view._num_shapes = self._root_view._physics_view.max_shapes
-            self._root_view._num_fixed_tendons = self._root_view._physics_view.max_fixed_tendons
-            self._root_view._body_names = self._root_view._metadata.link_names
-            self._root_view._body_indices = dict(
-                zip(self._root_view._body_names, range(len(self._root_view._body_names)))
-            )
-            self._root_view._dof_names = self._root_view._metadata.dof_names
-            self._root_view._dof_indices = self._root_view._metadata.dof_indices
-            self._root_view._dof_types = self._root_view._metadata.dof_types
-            self._root_view._dof_paths = self._root_view._physics_view.dof_paths
-            self._root_view._prim_paths = self._root_view._physics_view.prim_paths
-            carb.log_info(f"Articulation Prim View Device: {self._root_view._device}")
-            self._root_view._is_initialized = True
+        # We override their internal function that throws an error which is not desired or needed.
+        dummy_tensor = torch.empty(size=(0, 0), device=self.device)
+        dummy_joint_actions = ArticulationActions(dummy_tensor, dummy_tensor, dummy_tensor)
+        current_fn = self._root_view.get_applied_actions
+        self._root_view.get_applied_actions = lambda *args, **kwargs: dummy_joint_actions
+        # initialize the root view
+        self._root_view.initialize()
+        # restore the function
+        self._root_view.get_applied_actions = current_fn
+
         # -- link views
         # note: we use the root view to get the body names, but we use the body view to get the
         #       actual data. This is mainly needed to apply external forces to the bodies.

source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/rigid_object/rigid_object.py

@@ -295,7 +295,7 @@ class RigidObject(AssetBase):
         self._data.body_names = self.body_names
         # -- root states
         self._data.root_state_w = torch.zeros(self.root_view.count, 13, device=self.device)
-        self._data.default_root_state_w = torch.zeros_like(self._data.root_state_w)
+        self._data.default_root_state = torch.zeros_like(self._data.root_state_w)
         # -- body states
         self._data.body_state_w = torch.zeros(self.root_view.count, self.num_bodies, 13, device=self.device)
         # -- post-computed
@@ -320,7 +320,7 @@ class RigidObject(AssetBase):
             + tuple(self.cfg.init_state.ang_vel)
         )
         default_root_state = torch.tensor(default_root_state, dtype=torch.float, device=self.device)
-        self._data.default_root_state_w = default_root_state.repeat(self.root_view.count, 1)
+        self._data.default_root_state = default_root_state.repeat(self.root_view.count, 1)
 
     def _update_common_data(self, dt: float):
         """Update common quantities related to rigid objects.

source/extensions/omni.isaac.orbit/omni/isaac/orbit/assets/rigid_object/rigid_object_data.py

@@ -24,8 +24,8 @@ class RigidObjectData:
     # Default states.
     ##
 
-    default_root_state_w: torch.Tensor = None
-    """Default root state ``[pos, quat, lin_vel, ang_vel]`` in simulation world frame. Shape is ``(count, 13)``."""
+    default_root_state: torch.Tensor = None
+    """Default root state ``[pos, quat, lin_vel, ang_vel]`` in local environment frame. Shape is ``(count, 13)``."""
 
     ##
     # Frame states.

source/extensions/omni.isaac.orbit/omni/isaac/orbit/command_generators/position_command_generator.py

@@ -85,7 +85,7 @@ class TerrainBasedPositionCommandGenerator(CommandGeneratorBase):
         # TODO: need to add that here directly
         self.pos_command_w[env_ids] = self.terrain.sample_new_targets(env_ids)
         # offset the position command by the current root position
-        self.pos_command_w[env_ids, 2] += self.robot.data.default_root_state_w[env_ids, 2]
+        self.pos_command_w[env_ids, 2] += self.robot.data.default_root_state[env_ids, 2]
 
         if self.cfg.simple_heading:
             # set heading command to point towards target

source/extensions/omni.isaac.orbit/omni/isaac/orbit/envs/mdp/randomizations.py

@@ -192,7 +192,7 @@ def reset_root_state(
     # extract the used quantities (to enable type-hinting)
     asset: RigidObject | Articulation = env.scene[asset_cfg.name]
     # get default root state
-    root_states = asset.data.default_root_state_w[env_ids].clone()
+    root_states = asset.data.default_root_state[env_ids].clone()
 
     # positions
     pos_offset = torch.zeros_like(root_states[:, 0:3])
@@ -250,7 +250,7 @@ def reset_scene_to_default(env: BaseEnv, env_ids: torch.Tensor):
     # root states
     for rigid_object in env.scene.rigid_objects.values() + env.scene.articulations.values():
         # obtain default and deal with the offset for env origins
-        default_root_state = rigid_object.data.default_root_state_w[env_ids].clone()
+        default_root_state = rigid_object.data.default_root_state[env_ids].clone()
         default_root_state[:, 0:3] += env.scene.env_origins[env_ids]
         # set into the physics simulation
         rigid_object.write_root_state_to_sim(default_root_state, env_ids=env_ids)

source/extensions/omni.isaac.orbit/test/assets/check_external_force.py

@@ -97,7 +97,7 @@ def main():
             sim_time = 0.0
             count = 0
             # reset root state
-            root_state = robot.data.default_root_state_w.clone()
+            root_state = robot.data.default_root_state.clone()
             root_state[0, :2] = torch.tensor([0.0, -0.5], device=sim.device)
             root_state[1, :2] = torch.tensor([0.0, 0.5], device=sim.device)
             robot.write_root_state_to_sim(root_state)

source/extensions/omni.isaac.orbit/test/assets/test_articulation.py

@@ -129,7 +129,7 @@ class TestArticulation(unittest.TestCase):
         # Now we are ready!
         for _ in range(5):
             # reset root state
-            root_state = robot.data.default_root_state_w.clone()
+            root_state = robot.data.default_root_state.clone()
             root_state[0, :2] = torch.tensor([0.0, -0.5], device=self.sim.device)
             root_state[1, :2] = torch.tensor([0.0, 0.5], device=self.sim.device)
             robot.write_root_state_to_sim(root_state)
@@ -176,7 +176,7 @@ class TestArticulation(unittest.TestCase):
         # Now we are ready!
         for _ in range(5):
             # reset root state
-            root_state = robot.data.default_root_state_w.clone()
+            root_state = robot.data.default_root_state.clone()
             root_state[0, :2] = torch.tensor([0.0, -0.5], device=self.sim.device)
             root_state[1, :2] = torch.tensor([0.0, 0.5], device=self.sim.device)
             robot.write_root_state_to_sim(root_state)

source/extensions/omni.isaac.orbit/test/scene/check_interactive_scene.py

@@ -126,7 +126,7 @@ def main():
             sim_time = 0.0
             count = 0
             # reset root state
-            root_state = scene.articulations["robot_1"].data.default_root_state_w.clone()
+            root_state = scene.articulations["robot_1"].data.default_root_state.clone()
             root_state[:, :3] += scene.env_origins
             joint_pos = scene.articulations["robot_1"].data.default_joint_pos
             joint_vel = scene.articulations["robot_1"].data.default_joint_vel

source/extensions/omni.isaac.orbit/test/sensors/check_frame_transformer.py

@@ -204,7 +204,7 @@ def main():
             sim_time = 0.0
             count = 0
             # reset root state
-            root_state = scene.articulations["robot"].data.default_root_state_w.clone()
+            root_state = scene.articulations["robot"].data.default_root_state.clone()
             root_state[:, :3] += scene.env_origins
             joint_pos = scene.articulations["robot"].data.default_joint_pos
             joint_vel = scene.articulations["robot"].data.default_joint_vel

source/standalone/demo/play_scene.py

@@ -119,7 +119,7 @@ def main():
             sim_time = 0.0
             count = 0
             # reset root state
-            root_state = scene.articulations["robot_1"].data.default_root_state_w.clone()
+            root_state = scene.articulations["robot_1"].data.default_root_state.clone()
             root_state[:, :3] += scene.env_origins
             joint_pos = scene.articulations["robot_1"].data.default_joint_pos
             joint_vel = scene.articulations["robot_1"].data.default_joint_vel

source/standalone/demo/play_ycb_objects.py

@@ -95,7 +95,7 @@ def main():
             sim_time = 0.0
             count = 0
             # reset root state
-            root_state = rigid_object.data.default_root_state_w.clone()
+            root_state = rigid_object.data.default_root_state.clone()
             # -- position
             root_state[:, :3] = sample_cylinder(
                 radius=0.5, h_range=(0.15, 0.25), size=rigid_object.root_view.count, device=rigid_object.device