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Object Pose Estimation Tutorial: Part 1

In this first part of the tutorial, we will start by downloading and installing the Unity Editor. We will install our project's dependencies: the Perception, URDF, and TCP Connector packages. We will then use a set of provided prefabs to easily prepare a simulated environment containing a table, a cube, and a working robot arm.

Table of Contents

Requirements

To follow this tutorial you need to clone this repository even if you want to create your Unity project from scratch.

Note: This project uses Git Submodules to grab the ROS package dependencies for the universal_robot, moveit_msgs, ros_tcp_endpoint, and the robotiq folders.

Note: The ros-industrial/robotiq repository does not currently support ROS Noetic. The JSTech/robotiq#noetic-mods fork, which has been updated to use ROS Noetic, is used instead.

  1. Open a terminal and navigate to the folder where you want to host the repository.
git clone --recurse-submodules https://github.com/Unity-Technologies/Robotics-Object-Pose-Estimation.git
  1. Install Unity 2020.2.*.

Create a New Project

When you first run Unity, you will be asked to open an existing project, or create a new one.

  1. Open Unity and create a new project using the Universal Render Pipeline. Name your new project Pose Estimation Tutorial, and specify a desired location as shown below.

  1. Go to Edit > Project Settings to open the Project Settings window. Change the Physics > Solver Type to Temporal Gauss Seidel.

Download the Perception, the URDF and the TCP connector Packages

Once your new project is created and loaded, you will be presented with the Unity Editor interface. From this point on, whenever we refer to the "editor", we mean the Unity Editor.

How to install packages

We will need to download and install several packages. In general, packages can be installed in Unity with the following steps:

  • From the top menu bar, open Window -> Package Manager. As the name suggests, the Package Manager is where you can download new packages, update or remove existing ones, and access a variety of information and additional actions for each package.

  • Click on the + sign at the top-left corner of the Package Manager window and then choose the option Add package from git URL....

  • Enter the package address and click Add.

It can take a few minutes for the manager to download and import packages.

Install Dependencies

Install the following packages with the provided git URLs:

  1. Perception package - com.unity.perception@0.8.0-preview.3

    • This will help us collect training data for our machine learning model.

  2. URDF Importer package - https://github.com/Unity-Technologies/URDF-Importer.git?path=/com.unity.robotics.urdf-importer#v0.2.0-light

  3. TCP Connector package - https://github.com/Unity-Technologies/ROS-TCP-Connector.git?path=/com.unity.robotics.ros-tcp-connector#v0.2.0-light

    • This package will enable a connection between ROS and Unity.

Note: If you encounter a Package Manager issue, check the Troubleshooting Guide for potential solutions.

Set Up Ground Truth Renderer Feature

The Hierarchy, Scene, Game, Inspector, Project, and Console windows of the Unity Editor, as well as the Play/Pause/Step toolbar have been highlighted below for reference, based on the default layout. Custom Unity Editor layouts may vary slightly. A top menu bar option is available to re-open any of these windows: Window > General.

The Perception package relies on a "Ground Truth Renderer Feature" to output labeled images as training data. Follow the steps below to add this component to your rendering settings:

  1. The Project tab contains a search bar; use it to find the file named ForwardRenderer, and click on the file named ForwardRenderer.asset as shown below:

  1. Click on the found file to select it. Then, from the Inspector tab of the editor, click on the Add Renderer Feature button, and select Ground Truth Renderer Feature from the dropdown menu:

Set Up the Scene

The Scene

Simply put in Unity, a Scene contains any object that exists in the world. This world can be a game, or in this case, a data-collection-oriented simulation. Every new project contains a Scene named SampleScene, which is automatically opened when the project is created. This Scene comes with several objects and settings that we do not need, so let's create a new one.

  1. In the Project tab, right-click on the Assets/Scenes folder and click Create -> Scene. Name this new Scene TutorialPoseEstimation and double-click on it to open it.

The Hierarchy tab of the editor displays all the Scenes currently loaded, and all the objects currently present in each loaded Scene, as shown below:

As seen above, the new Scene already contains a camera (Main Camera) and a light (Directional Light). We will now modify the camera's field of view and position to prepare it for the tutorial.

  1. Still in the Inspector tab of the Main Camera, modify the camera's Position and Rotation to match the values shown below. This orients the camera so that it will have a good view of the objects we are about to add to the scene.

  1. Click on Directional Light and in the Inspector tab, modify the light's Position and Rotation to match the screenshot below.

Adding Tutorial Files

Now it is time to add some more objects to our scene. Before doing so, we need to import some folders containing the required assets.

  1. Download TutorialAssets.zip, and unzip it. It should contain the following subfolders: Materials, Prefabs, RosMessages, Scripts, URDFs.

  2. Drag and Drop the TutorialAssets folder from your operating system's file explorer onto the Assets folder in the Project tab of the editor.

Your Assets folder should like this:

Using Prefabs

Unity’s Prefab system allows you to create, configure, and store a GameObject complete with all its components, property values, and child GameObjects as a reusable Unity Asset. It is a convenient way to store complex objects.

A Prefab is just a file, and you can easily create an instance of the object in the scene from a Prefab by dragging it into the Hierarchy tab.

For your convenience, we have provided Prefabs for most of the components of the scene (the cube, goal, table, and floor).

  1. In the Project tab, go to Assets/TutorialAssets/Prefabs/Part1 and drag and drop the Cube Prefab into the Hierarchy tab.

  2. Repeat the above action with the Goal, Table and Floor Prefabs.

Note: If you encounter issues with the materials of the imported Prefabs, check the Troubleshooting Guide for potential solutions.

Importing the Robot

Finally we will add the robot and the URDF files in order to import the UR3 Robot.

  1. In the Project tab, go to Assets/TutorialAssets/URDFs/ur3_with_gripper and right click on the ur3_with_gripper.urdf file and select Import Robot From Selected URDF file. A window will pop up, keep the default Y Axis type and VHACD Mesh Decomposer in the Import menu. Then, click Import URDF. These actions are shown in the video below.

Note: Unity uses a left-handed coordinate system in which the y-axis points up. However, many robotics packages use a right-handed coordinate system in which the z-axis or x-axis point up. For this reason, it is important to pay attention to the coordinate system when importing URDF files or interfacing with other robotics software.

Note: The VHACD algorithm produces higher quality convex hull for collision detection than the default algorithm.

Note: If you encounter issues with importing the robot, check the Troubleshooting Guide for potential solutions.

Setting up the Robot

  1. In the Hierarchy tab, select the ur3_with_gripper GameObject and in the Inspector view, go to the Controller script and set the Stiffness to 10000, the Damping to 1000 and the Force Limit to 1000. These are physics properties that control how the robot moves.

  2. In the Hierarchy tab, click on the arrow to the left of the ur3_with_gripper GameObject to expand it, then expand world, and select base_link. In the Articulation Body component, toggle on Immovable. This will fix the robot base to its current position.

Proceed to Part 2.