GUI

Omnigraph

OmniGraph:
Omniverse’s visual programming framework
-Provides a graph framework that can easily connect functions from multiple systems inside Omniverse
-Is also a compute framework that allows for highly customized nodes so that users can integrate their own functionality into Omniverse and automatically harness the efficient computation backend
-Inside Omniverse Isaac Sim, OmniGraph is the main engine behind the Replicators, ROS and ROS2 bridges, access to many sensors, controllers, external input/output devices, UI, and much more
-Fast introduction into the world of visual programming via OmniGraph

Learning Objectives

Details build an action graph to control a robot in Omniverse Isaac Sim, specifically, the Jetbot
Goal: Give you a fast introduction to using Action Graphs in Omniverse Isaac Sim

Getting Started

Prerequisites:
Review Isaac Sim Interface prior to beginning this tutorial
Check out Assemble a Simple Robot for details on how you setup your own robot

Setting up the stage

1)On a new stage, start by right clicking and selecting Create > Physics > Ground Plane

2) Next, use the content browser to navigate to Isaac/Robots/JetBot and click and drag jetbot.usd onto the stage
Position the jetbot just above the ground plane. When completed, the jetbot should be under /World/jetbot in the context tree and the stage should look similar to this



Pressed F button
Depending on your default render settings, the camera of the jetbot may have a placeholder mesh (it looks like a gray Television camera)
To hide these meshes, click on the eyecon icon in the viewports, and then select Show By Type –> Cameras to hide the placeholder mesh
3)Building the graph
(3)-1 Select Window -> Visual Scripting -> Action Graph from the dropdown menu at the top of the editor

The Graph Editor will appear in the same pane as the Content browser
(3)-2 Click New Action Graph to open an empty graph

(3)-3 Type controller in the search bar of the graph editor

(3)-4 Drag an Articulation Controller and a Differential Controller onto the graph

(3)-5 Articulation Controller:
Applies driver commands(In the form of force, position, or velocity) to the specified joints of any prim with an articulation root
To tell the controller which robot it’s going to control
First select the Articulation Controller node in the graph and open up the property pane.

Can either keep usePath checked and type in the path to the robot /World/jetbot in the robotPath
Can uncheck usePath and then click Add Targets near the top of the pane for input:targetPrim, and select jetbot in the pop up window
(3)-6 Differential Controller:
Computes drive commands for a two wheeled robot given some target linear and angular velocity like the Articulation Controller, it also needs to be configured

Select the Differential Controller node in the graph, and then in the properties pane, set the wheelDistance to 0.1125, the wheelRadius to 0.03, and maxAngularSpeed to 0.2
(3)-7 Identify joints for articulation
Articulation Controller has the needs to know which joints to articulate
-Expects this information in the form of a list of tokens or index values

Each joint in a robot has a name and the jetbot has exactly two
Within /World/jetbot/chassis are two revolute physics joints named left_wheel_joint and right_wheel_joint
(3)-8 Add tokens
Type token into the search bar of the graph editor and add two Constant Token nodes to the graph


(3)-9 Type in values


Select one, and set it’s value to left_wheel_joint in the properties pane
Repeat this for the other constant token node, but set the value to right_wheel_joint
(3)-10 Make arrays

Type make array into the search bar of the graph editor and add a Make Array node to the graph

Drag and drop make array node

Select the Make Array node and click on the + icon in the inputs section of the property pane menu to add a second input
Set the arraySize to 2 as well, and then set the input type to token[] from the dropdown menu in the same pane
(3)-11 Connect Constant Token Nodes

Finally, connect the constant token nodes to A and B of the Make Array node, and then the output of that node to the Joint Names input of the Articulation Controller node
(3)-12 Add Event Node
The last node is the event node

Search for playback in the search bar of the graph editor

Add an On Playback Tick node to the graph
This node will emit an execution event for every frame, but only while the simulation is playing
Connect the Tick output of the On Playback Tick node to the Exec In input of both controller nodes
Connect the Velocity Command output of the differential controller to the Velocity Command input of the articulation controller
(3)-13 Completed Omnigraph

(3)-14 Play

Press the play button and select the Differential Controller Node in the graph
Click and drag on either the angular or linear velocity values in the properties pane to change it’s value (or just click and type in the desired value)

File Path:
https://drive.google.com/file/d/1MFl4FTeDXb3dS7pQkWbeW-c0f_KwJ2J7/view?usp=sharing
Reference:
https://docs.omniverse.nvidia.com/isaacsim/latest/gui_tutorials/tutorial_gui_omnigraph.html