7.1.16. RTX Lidars

RTX or Raytraced lidar is an alternative to the PhysX lidar in Isaac Sim. It supports both Solid State and Rotating Lidar configuration via a JSON config file. Each RTX Sensor must be attached to its own viewport to simulate properly.

Warning

Docking windows in the isaac-sim UI when an RTX Lidars simulation is running will likely lead to a crash. Please pause the simulation before re-docking the window.

7.1.16.1. Learning Objectives

In this example, we will

Have a brief introduction on how to use RTX Lidar sensors
Create a RTX Lidar sensor
Publish sensor data to ROS as a PointCloud2 and LaserScan message

7.1.16.2. Getting Started

Prerequisites

Completed the ROS Cameras and URDF Import: Turtlebot tutorial.
ROS bridge is enabled and roscore is running.
OPTIONAL: Explore the inner workings of RTX Lidar sensors by learning How They work, the RTX Lidar Nodes that use them, and how to get RTX Lidar Synthetic Data.

7.1.16.3. Creating RTX Lidar and Publishing Lidar data over ROS:

Start Isaac Sim and ensure the ROS1 bridge is enabled (Window->Extensions). Add a few objects in the scene (eg Cone and cube, keep them away from the origin)
Create a Rotating RTX Lidar sensor: Create->Isaac->Sensors->RTX Lidar->Rotating
Create Visual Scripting->Action Graph. Next, add the following nodes to this graph:
1. On Playback Tick: This is the node responsible for triggering all the other nodes once ‘Play’ is pressed.
2. Isaac Create Render Product: In the input camera prim select the RTX Lidar created in step 2.
3. ROS1 RTX Lidar Helper: This node will handle publishing of the laser scan message from the rtx lidar. The input render product is obtained from the output of Isaac Create Render Product in step b.
4. ROS1 RTX Lidar Helper: This node will handle publishing the point cloud from the rtx lidar. Under input type select ‘point_cloud’ and change the topic name to point_cloud. The input render product is obtained from the output of Isaac Create Render Product in step b.

Once the graph has been set correctly, hit ‘Play’ to begin simulation. The RTX Lidar should be sending the LaserScan and PointCloud2 messages and can be visualized in RViZ.

For RViZ visualization:

Run RViZ (rosrun rviz rviz) in a sourced terminal.
Set fixed frame as ‘sim_lidar’
Add LaserScan visualization and set topic to /scan
Add PointCloud2 visualization and set topic to /point_cloud

7.1.16.4. Running The Example

In one terminal source your ROS workspace and run roscore
In a new terminal with your ROS environment sourced, run rviz -d <noetic_ws>/src/isaac_tutorials/rviz/rtx_lidar.rviz to start rviz and show the lidar point cloud

Finally, run the sample script

./python.sh standalone_examples/api/omni.isaac.ros_bridge/rtx_lidar.py

Once the scene finishes loading you should see the point cloud for the rotating lidar sensor being simulated

7.1.16.5. RTX Lidar Script sample

While most of the sample code is fairly generic, there are a few specific pieces needed to create and simulate the sensor

We first need to create the RTX Lidar Sensor

_, sensor = omni.kit.commands.execute(
    "IsaacSensorCreateRtxLidar",
    path="/sensor",
    parent=None,
    config="Example_Rotary",
    translation=(0, 0, 1.0),
    orientation=Gf.Quatd(0.5, 0.5, -0.5, -0.5),
)

Here Example_Rotary defines the configuration for the lidar sensor. The two generic configuration files provided are located in exts/omni.drivesim.sensors.nv.lidar/data. Example_Rotary.json and Example_Solid_State.json. To switch the lidar to the example solid state configuration you can replace config=”Example_Rotary”, with config=”Example_Solid_State”.

Next, we need create a render product and attach this sensor to it

render_product = rep.create.render_product(sensor.GetPath(), [1, 1])

We can then create the post process pipeline that takes the rendered RTX Lidar data and publishes it to ROS:

sensors.get_synthetic_data().activate_node_template("RtxLidar" + "ROSPublishPointCloud", 0, [render_product.path])

Note

You can specify an optional attributes={…} dictionary when calling activate_node_template to set node specific parameters. See the API Documentation for complete usage information.

7.1.16.6. Summary

This tutorial covered creating and using the RTX Lidar Sensor with ROS.