Reads gravity direction from simulation inside `RigidObjectData` (#582)

# Description

Previously, the gravity direction inside the `RigidObjectData` class was
hard-coded as (0, 0, -1). However, this quantity may have a different
direction in some simulation situations. This MR removes this hard
coding and directly reads the value from the simulation view.

## Type of change

- Bug fix (non-breaking change which fixes an issue)
- New feature (non-breaking change which adds functionality)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have run all the tests with `./isaaclab.sh --test` and they pass
- [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.lab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.18.4"
+version = "0.18.5"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

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

 Changelog
 ---------
 
+0.18.5 (2024-06-26)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed the gravity vector direction used inside the :class:`omni.isaac.lab.assets.RigidObjectData`class.
+  Earlier, the gravity direction was hard-coded as (0, 0, -1) which may be different from the actual
+  gravity direction in the simulation. Now, the gravity direction is obtained from the simulation context
+  and used to compute the projection of the gravity vector on the object.
+
+
 0.18.4 (2024-06-26)
 ~~~~~~~~~~~~~~~~~~~
 

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

@@ -45,8 +45,16 @@ class RigidObjectData:
         # Set initial time stamp
         self._sim_timestamp = 0.0
 
+        # Obtain global physics sim view
+        physics_sim_view = physx.create_simulation_view("torch")
+        physics_sim_view.set_subspace_roots("/")
+        gravity = physics_sim_view.get_gravity()
+        # Convert to direction vector
+        gravity_dir = torch.tensor((gravity[0], gravity[1], gravity[2]), device=self.device)
+        gravity_dir = math_utils.normalize(gravity_dir.unsqueeze(0)).squeeze(0)
+
         # Initialize constants
-        self.GRAVITY_VEC_W = torch.tensor((0.0, 0.0, -1.0), device=self.device).repeat(self._root_physx_view.count, 1)
+        self.GRAVITY_VEC_W = gravity_dir.repeat(self._root_physx_view.count, 1)
         self.FORWARD_VEC_B = torch.tensor((1.0, 0.0, 0.0), device=self.device).repeat(self._root_physx_view.count, 1)
 
         # Initialize buffers for finite differencing
@@ -121,12 +129,7 @@ class RigidObjectData:
 
     @property
     def projected_gravity_b(self):
-        """Projection of the gravity direction on base frame. Shape is (num_instances, 3).
-
-        Note:
-            This quantity is computed by assuming that the gravity direction is along the z-direction,
-            i.e. :math:`(0, 0, -1)`.
-        """
+        """Projection of the gravity direction on base frame. Shape is (num_instances, 3)."""
         return math_utils.quat_rotate_inverse(self.root_quat_w, self.GRAVITY_VEC_W)
 
     @property

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/mdp/events.py

@@ -19,6 +19,7 @@ import warnings
 from typing import TYPE_CHECKING, Literal
 
 import carb
+import omni.physics.tensors.impl.api as physx
 
 import omni.isaac.lab.sim as sim_utils
 import omni.isaac.lab.utils.math as math_utils
@@ -206,7 +207,12 @@ def randomize_physics_scene_gravity(
     """Randomize gravity by adding, scaling, or setting random values.
 
     This function allows randomizing gravity of the physics scene. The function samples random values from the
-    given distribution parameters and adds, scales, or sets the values into the physics simulation based on the operation.
+    given distribution parameters and adds, scales, or sets the values into the physics simulation based on the
+    operation.
+
+    The distribution parameters are lists of two elements each, representing the lower and upper bounds of the
+    distribution for the x, y, and z components of the gravity vector. The function samples random values for each
+    component independently.
 
     .. attention::
         This function applied the same gravity for all the environments.
@@ -225,9 +231,13 @@ def randomize_physics_scene_gravity(
         slice(None),
         operation=operation,
         distribution=distribution,
-    )[0]
+    )
+    # unbatch the gravity tensor into a list
+    gravity = gravity[0].tolist()
+
     # set the gravity into the physics simulation
-    sim_utils.SimulationContext.instance().physics_sim_view.set_gravity(carb.Float3(gravity[0], gravity[1], gravity[2]))
+    physics_sim_view: physx.SimulationView = sim_utils.SimulationContext.instance().physics_sim_view
+    physics_sim_view.set_gravity(carb.Float3(*gravity))
 
 
 def randomize_actuator_gains(
@@ -841,7 +851,7 @@ Internal helper functions.
 
 def _randomize_prop_by_op(
     data: torch.Tensor,
-    distribution_parameters: tuple[float, float],
+    distribution_parameters: tuple[float | torch.Tensor, float | torch.Tensor],
     dim_0_ids: torch.Tensor | None,
     dim_1_ids: torch.Tensor | slice,
     operation: Literal["add", "scale", "abs"],

source/extensions/omni.isaac.lab/test/assets/test_rigid_object.py

@@ -149,7 +149,7 @@ class TestRigidObject(unittest.TestCase):
                             # check that the object is kinematic
                             default_root_state = cube_object.data.default_root_state.clone()
                             default_root_state[:, :3] += origins
-                            torch.testing.assert_allclose(cube_object.data.root_state_w, default_root_state)
+                            torch.testing.assert_close(cube_object.data.root_state_w, default_root_state)
 
     def test_initialization_with_no_rigid_body(self):
         """Test that initialization fails when no rigid body is found at the provided prim path."""
@@ -627,6 +627,36 @@ class TestRigidObject(unittest.TestCase):
                         # Check if mass is set correctly
                         torch.testing.assert_close(masses, masses_to_check)
 
+    def test_gravity_vec_w(self):
+        """Test that gravity vector direction is set correctly for the rigid object."""
+        for num_cubes in (1, 2):
+            for device in ("cuda:0", "cpu"):
+                for gravity_enabled in [True, False]:
+                    with self.subTest(num_cubes=num_cubes, device=device, gravity_enabled=gravity_enabled):
+                        with build_simulation_context(device=device, gravity_enabled=gravity_enabled) as sim:
+                            cube_object, _ = generate_cubes_scene(num_cubes=num_cubes, device=device)
+
+                            # Obtain gravity direction
+                            if gravity_enabled:
+                                gravity_dir = (0.0, 0.0, -1.0)
+                            else:
+                                gravity_dir = (0.0, 0.0, 0.0)
+
+                            # Play sim
+                            sim.reset()
+
+                            # Check that gravity is set correctly
+                            self.assertEqual(cube_object.data.GRAVITY_VEC_W[0, 0], gravity_dir[0])
+                            self.assertEqual(cube_object.data.GRAVITY_VEC_W[0, 1], gravity_dir[1])
+                            self.assertEqual(cube_object.data.GRAVITY_VEC_W[0, 2], gravity_dir[2])
+
+                            # Simulate physics
+                            for _ in range(2):
+                                # perform rendering
+                                sim.step()
+                                # update object
+                                cube_object.update(sim.cfg.dt)
+
 
 if __name__ == "__main__":
     run_tests()