Import URDF#

Learning Objectives#

This tutorial shows how to import a urdf and convert it to a usd in Omniverse Isaac Sim. After this tutorial, you can use urdf files in your pipeline while using Omniverse Isaac Sim.

5-10 Minute Tutorial

Getting Started#

Prerequisites

Using the URDF Importer Extension Window#

Let’s begin by importing a Franka Panda URDF from the Built in URDF files that come with the extension.

  1. Enable the omni.importer.urdf extension in Omniverse Isaac Sim if it is not automatically loaded by going to Window-> Extensions and enable omni.importer.urdf.

    Enable URDF Importer

  2. Accessed the urdf externsion by going to the Isaac Utils -> Workflows -> URDF Importer menu.

    User interface for URDF Importer

  3. Let’s specify the settings we want to import Franka with:

    • Check the box next to Fix Base Link, and Create Physics Scene only.

    • Set Stage Units Per Meters to 1.0, which means the asset will be imported in meters

    • Set the joint drive type to Position

    • Set Joint Drive Strength and Joint Position Drive Damping to 10000000.0 and 100000.0

    • Set the Output Directory to the place where you store your assets (nucleus or Local)

    Note

    You must have write access to the output directory used for import, it will default to the current open stage, change this as necessary.

  4. In the file Input File box under the Import tab, navigate to the desired folder, and select the desired URDF file. For this example, we will use the Franka panda_arm_hand.urdf file that is included in the Built in URDF Files/robots/franka_description/robots folder that comes with this extension.

    Select URDF to Import Select URDF to Import 2

  5. Click the Import button to add the robot to the stage.

    Imported Franka

  6. Visualize the collision meshes, not all the rigid bodies need to have collision properties, and collision meshes are often a simplified mesh compared to the visual ones. Therefore you may want to visualize the collision mesh for inspection. To visualize collision in any viewport:

    • Select: the eye icon in the upper left corner of the viewport.

    • Select: Show by type.

    • Select: Physics.

    • Select: Colliders.

    • Check: All.

    ../_images/isaac_physics_visualize_collision.png

  7. If you are importing a mobile robot, you may need to change the following settings

    • Uncheck Fix Base Link

    • Set the joint drive type to Velocity drive

    • Set the Joint Drive Strength to the desired level. Note that this will be imported as the joint’s damping parameter. Joint stiffness are always set to 0 in velocity drive mode.

Importing URDF using Python#

Let’s do the exact same things as we did before but with python scripting instead. We will then use the imported robot with one of the tasks defined under omni.isaac.franka extension to follow a target in the stage.

  1. Let’s begin by opening the Hello World example. Go to the top Menu Bar and Click Isaac Examples > Hello World.

  2. The window for the Hello World example extension should now be visible in the workspace.

  3. Click the Open Source Code button to launch the source code for editing in Visual Studio Code.

  4. Edit the hello_world.py file as shown below.

     1from omni.isaac.examples.base_sample import BaseSample
 2from omni.isaac.core.utils.extensions import get_extension_path_from_name
 3from omni.importer.urdf import _urdf
 4from omni.isaac.franka.controllers import RMPFlowController
 5from omni.isaac.franka.tasks import FollowTarget
 6import omni.kit.commands
 7import omni.usd
 8
 9class HelloWorld(BaseSample):
10    def __init__(self) -> None:
11        super().__init__()
12        return
13
14    def setup_scene(self):
15        world = self.get_world()
16        world.scene.add_default_ground_plane()
17        # Acquire the URDF extension interface
18        urdf_interface = _urdf.acquire_urdf_interface()
19        # Set the settings in the import config
20        import_config = _urdf.ImportConfig()
21        import_config.merge_fixed_joints = False
22        import_config.convex_decomp = False
23        import_config.fix_base = True
24        import_config.make_default_prim = True
25        import_config.self_collision = False
26        import_config.create_physics_scene = True
27        import_config.import_inertia_tensor = False
28        import_config.default_drive_strength = 1047.19751
29        import_config.default_position_drive_damping = 52.35988
30        import_config.default_drive_type = _urdf.UrdfJointTargetType.JOINT_DRIVE_POSITION
31        import_config.distance_scale = 1
32        import_config.density = 0.0
33        # Get the urdf file path
34        extension_path = get_extension_path_from_name("omni.importer.urdf")
35        root_path = extension_path + "/data/urdf/robots/franka_description/robots"
36        file_name = "panda_arm_hand.urdf"
37        # Finally import the robot
38        result, prim_path = omni.kit.commands.execute( "URDFParseAndImportFile", urdf_path="{}/{}".format(root_path, file_name),
39                                                      import_config=import_config,)
40        # Optionally, you could also provide a `dest_path` parameter stage path to URDFParseAndImportFile,
41        # which would import the robot on a new stage, in which case you'd need to add it to current stage as a reference:
42        #   dest_path = "/path/to/dest.usd
43        #   result, prim_path = omni.kit.commands.execute( "URDFParseAndImportFile", urdf_path="{}/{}".format(root_path, file_name),
44        # import_config=import_config,dest_path = dest_path)
45        #   prim_path = omni.usd.get_stage_next_free_path(
46        #       self.world.scene.stage, str(current_stage.GetDefaultPrim().GetPath()) + prim_path, False
47        #   )
48        #   robot_prim = self.world.scene.stage.OverridePrim(prim_path)
49        #   robot_prim.GetReferences().AddReference(dest_path)
50        # This is required for robot assets that contain texture, otherwise texture won't be loaded.
51
52        # Now lets use it with one of the tasks defined under omni.isaac.franka
53        # Similar to what was covered in Tutorial 6 Adding a Manipulator in the Required Tutorials
54        my_task = FollowTarget(name="follow_target_task", franka_prim_path=prim_path,
55                               franka_robot_name="fancy_franka", target_name="target")
56        world.add_task(my_task)
57        return
58
59    async def setup_post_load(self):
60        self._world = self.get_world()
61        self._franka = self._world.scene.get_object("fancy_franka")
62        self._controller = RMPFlowController(name="target_follower_controller", robot_articulation=self._franka)
63        self._world.add_physics_callback("sim_step", callback_fn=self.physics_step)
64        await self._world.play_async()
65        return
66
67    async def setup_post_reset(self):
68        self._controller.reset()
69        await self._world.play_async()
70        return
71
72    def physics_step(self, step_size):
73        world = self.get_world()
74        observations = world.get_observations()
75        actions = self._controller.forward(
76            target_end_effector_position=observations["target"]["position"],
77            target_end_effector_orientation=observations["target"]["orientation"],
78        )
79        self._franka.apply_action(actions)
80        return

  5. Press Ctrl+S to save the code and hot-reload Omniverse Isaac Sim.

  6. Click the File > New From Stage Template > Empty to create a new stage. Click Don’t Save if the simulator is prompting you to save the stage.

  7. Open the menu again and load the example.

  8. Click the LOAD button and move the target prim around

    ../_images/isaac_sim_import_urdf.gif

Summary#

This tutorial covered the following topics:

  1. Importing URDF file using GUI

  2. Importing URDF file using Python

  3. Using the imported URDF in a Task

  4. Visualizing collision meshes

Further Learning#

Checkout URDF Importer to learn more about the different configuration settings to import a urdf in Omniverse Isaac Sim.

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