AirStack Scene Setup

Creating a New Scene with Robots

The easiest way to create a scene is to copy and customize an existing scene.

Example scenes are located on the AirLab Nucleus Server under Projects > AirStack. This can be opened in Isaac's Content Browser:

For example, simple_tree_one_drone.scene.usd looks like this:

The example scenes are setup with the following:

• A "World" prim, which is the root of the scene
• The Root layer is set to use meters as the unit of length
• Prims that make up the scene. Scene prims should have collision physics enabled with Colliders Preset (Property > Add > Physics > Collider Preset)
• Robot instances, added to the scene as a reference to the robot USD file. Currently this file is Library > Assets > Ascent_Aerosystems > TEMPLATE_spirit_uav.robot.usd
• The robot has default sensors added, including a LiDAR and stereo cameras
• Sensors publish to ROS using the attached ActionGraph
• Robot dynamics are controlled by the AirStack Extension

Configure Robot Name and ROS_DOMAIN_ID

Under the Spirit drone prim is an ActionGraph component, which is an Omnigraph. This component is used to configure the ROS publishers for the robot. The ActionGraph component has the following fields to configure:

• ROBOT_NAME: The name of the robot. This is used as the top-level namespace for ROS topics.
• ROS_DOMAIN_ID: The ROS domain ID. This sets the ROS_DOMAIN_ID environment variable for DDS networking.

The Omnigraph has subgraphs for each ROS publisher type. For example, TFs, Images, and PointClouds. The top-level robot_name and domain_id fields get fed into the subgraphs.

To create a new robot, duplicate the drone prim instance and adjust the ROBOT_NAME and ROS_DOMAIN_ID fields to be unique.

Customizing the Omnigraph

Common pre-built graphs for ROS may be added through the top menu bar: Isaac Utils > Common OmniGraphs. This is helpful for creating various sensor publishers.

We recommend organizing your work into sub-graphs. Copy your omnigraph template them into the top-level Omnigraph component, named "ActionGraph". Connect the robot_name and domain_id fields to your workflow. Then, select all the nodes in your workflow, right-click, and create a subgraph.

Frame Conventions

Isaac Sim uses Forward-Left-Up (FLU) coordinate frame conventions. However, MAVROS and AirStack use East-North-Up (ENU).

To address this, the origin of the robot lives under a prim called map_FLU. Then AirStack publishes a static transform (static_transforms.launch.xml) from map_FLU to map, which is in ENU. The transform is a 90 degree rotation about the Z-axis.

The resulting TF tree looks like this: