OptiTrack OpenXR Plugin

A Quick Start Guide for using OptiTrack's OpenXR Plugin.

Overview

The OptiTrack OpenXR plugin allows Motive to connect to a Head-Mounted Display (HMD) to provide movement tracking to the device. This guide details the required software you must install to stream to a game engine or other platforms.

HMD Software Platform

Download and install the software platform that supports your HMD from the manufacturer.

All HMDs require their own software to connect the headset to the computer. This typically includes a user interface with systems that allow the HMD to be recognized by programs such as SteamVR, games, and other VR/XR applications.

Follow the HMD manufacturer's instructions to download and setup the applicable software for the HMD device.

Connect the HMD to the Motive Computer

Connect the HMD to the Motive computer via the HMD's software platform. This example uses the Meta Quest 2 and the Meta Quest Link App.

In our testing, we connected the HMD via a quest link cable (USB-C) designed specifically for the strongest signal connection between the HMD and PC. You can also use a wireless connection, which requires access to a Wi-Fi signal on on the HMD as well as the PC.

The Meta Quest 2 HMD. The red-circled X in the status indicates that audio is disabled, while the HMD is active.

Set the Framerate for Tracking

Every HMD has a refresh rate for its display. Some HMDs run at a lower refresh rate to address issues such as battery life, resolution, and overall performance, but they also include the option to increase their refresh rate.

When using Motive and the OptiTrack OpenXR Plugin, Motive must either match or be a multiple of the refresh rate of the HMD.

In the example below, the Quest 2 is running at a refresh rate of 72Hz, which is the recommended rate for the device. In Motive, the camera frame rate is set at twice that rate, 144Hz, for better tracking and a smoother experience.

SteamVR

To use the plugin, create a Steam account and download SteamVR from the Steam Store here.

The OptiTrack OpenXR Plugin injects code into the OpenXR runtime, to use tracking data from Motive for the HMD and controllers, overriding the position and rotation values for each.

The SteamVR interface includes options to select the OpenXR API layers, which includes Motive Tracking.

Activating the OpitTrack OpenXR plugin from the SteamVR settings.

Install the OptiTrack OpenXR Plugin

• Download and install the OptiTrack OpenXR plugin from the software plugins downloads page.

• Select the plugin's install destination as C:\Program Files\OptiTrack\.

• The OptiTrack OpenXR Config Application appears on the desktop once the installer has finished running.

Setting Up the OpenXR Plugin Config App

The OpenXR Config App is the interface to control settings for the OpenXR Plugin.

We strongly recommend using IMU Sensor Fusion for this workflow.

Tracking the HMD using an IMU sensor fused device in Motive provides the smoothest results. Without IMU sensor fusion, performance in XR experiences can be unstable or uncomfortable.

When the Rigid Body is Sensor Fused in Motive and connected to the Config App, an indicator appears as green, indicating complete tracking.

To configure:

1. Launch the OptiTrack OpenXR Config App.

2. Set the connection type to the preferred connection type. We recommend Unicast when streaming with multiple devices in the same Motive server. For more information on streaming in Motive, see the Settings: Streaming page.

3. Rigid Body ID: Verify that the Streaming ID matches the ID of the Rigid Body HMD you are tracking in Motive. This value is shown in the Rigid Body Properties or the Assets pane.

4. IPD: The HMD device has an Interpupillary Distance value, commonly known as IPD. Set this value in the Config App to match the IPD value shown on the HMD display when adjusting this distance in the lenses.

5. Controller Left/Right: Click the Enable Override toggle to track controllers using the Rigid Bodies in Motive. Verify and input the corresponding Rigid Body ID with the associated controller in Motive.

6. Status: When the two values match, the status indicator at the bottom turns green and displays the text, "Connected to Motive." If the rigid bodies are enabled but not detected, the status indicator is yellow, with the message, "Rigid Body IDs not found."

7. Click Save to save the profile for use within the API Layer for OpenXR.

Once the initial connection to Motive is established, the Config App can be closed. The OpenXR plugin uses the properties in the saved profile each time the HMD and controllers are connected.

To change the settings, launch the Config App and make the required changes or use the Load button to import a previous configuration.

SteamVR Setup

1. Launch SteamVR.

2. Go to Settings.

The SteamVR menu.

1. Click OpenXR on the left tab and select Manage OpenXR API Layers.

2. Set the Optitrack OpenXR Tracking Solution to On.

When using a Meta HMD, we recommend setting SteamVR as the OpenXR runtime source instead of Meta to avoid any graphical or tracking issues.

Connect to Game Engine

You can now launch your VR apps and platforms such as Unity or Unreal Engine with HMD tracking coming from Motive. To troubleshoot whether tracking is working, open the app and disable and re-enable the Rigid Body Tracking in Motive.

Special Note for Quest HMD Users

In our testing, when using a Quest HMD, we found that the OpenXR Runtime needs to be set to Quest to use in Unity, and it needs to be set to SteamVR to use in Unreal Engine.

Troubleshooting

Config App Fails to Load

After installation, launching the Configuration App from the Windows Start menu might return an error:

If this occurs, restarting Windows resolves the issue.

If restarting the PC is not possible, use the desktop shortcut to open the app, or right-click the app on the start menu and select Run as Administrator.

Sample App

The Configuration app includes a Sample App on the Tools menu to test and verify tracking results from Motive.

The Sample App launches a 3D scene of a 2x2m space in the HMD. The plugin version is displayed on the wall, and the floor grid shows the axis conventions. Use the text on the wall as well as the grid to orient yourself, compare origin positions, and validate tracking framerate consistency.

Log

The Log window is a helpful debugging tool that shows what actions and functions are happening through the OptiTrack OpenXR Plugin. You can access it from the View menu.