Unreal Engine: HMD Setup
For integrating Vive HMDs, the OptiTrack OpenVR Driver must be used. This driver lets you track the head-mounted display (HMD) and the VR controllers using OptiTrack motion capture system and stream the tracking data from Motive directly into SteamVR. In other words, this will basically override the tracking from the lighthouse stations. The plugin ships as an installer package (MSI) which will set up the driver along with a utility tool for configuring client streaming settings. Once integrated, the streamed tracking data can be used in any application platform that utilizes SteamVR. For tracking of objects other than the HMDs, please read through the OptiTrack Unreal Engine Plugin page for details.
- Vive Pro 1/2
- Valve Index
- HP Reverb G2
When developing for SteamVR applications using the OpenVR Driver to track the HMD in Unreal Engine 4, the OptiTrack - Streaming Client version 2.27 must be used and the OptiTrack - VR Latency Optimization version 2.27 plugin is suggested. The OptiTrack - VR Latency Optimization provides HMD render compensation that helps to minimize the latency in VR application.
OptiTrack plugins listed in UE4.
The latest plugins that support Unreal Engine 5 are OptiTrack - Live Link version 3.0 and OptiTrack - Streaming Client version 3.0.
OptiTrack plugins listed in UE5.
First of all, setup and optimize the motion capture volume as explained in the Getting Started guide or the Hardware Setup documentation. If you plan to install any obstacles (e.g. walls) within the capture volume, make sure they are non-reflective, and place and orient the cameras so that every corner is thoroughly captured by multiple cameras.
General Setup Steps
- 1.Attach the markers on the HMD
- 2.Create a Rigid Body asset
- 3.Calibrate the Pivot Point of the Rigid Body
- 4.Configure the Rigid Body settings in Motive
For the camera system to track the HMD, a set of markers must be attached to the HMD. You can either use the active markers (Active HMD clip or Active Tags) or the passive markers. Passive markers are retroreflective markers that reflect infrared light emitted from the IR LEDs on the camera. On the other hand, the active markers are LED markers that emit the IR light and has the intelligence to be uniquely identified.
In general, for most VR applications, using active markers is recommended for better tracking stability and ease of use. Active markers also have advantages over passive markers when tracking a large number of objects. For applications that are sensitive to the accuracy of the tracking data, using passive marker may have more benefits. To get more help with finding the best solution for your tracking application, please contact us.
When using the active markers, you can conveniently put a set of 8 markers onto the HMD by using the HMD Clip, or you can attach the markers from the Tag manually onto the HMD using adhesives and marker posts.
Active HMD Clip
Active HMD Clip is an HMD enclosure with a total of 8 active markers embedded for tracking. At the time of writing, there are active HMD clips for Vive Pro / Valve Index HMDs available on the webstore. The clips can be mounted easily by pushing it onto the HMD until the latches click, and you can detach it by gently lifting the three latches located at the top, left, and right side of the clip.
Once the clip has been mounted, next step is to import the provided Rigid Body asset into Motive and refine the definition to get the calibrated pivot point position and orientation, which will be explained on the next section.
Active marker clip for HTC Vive Pro.
Active marker clip for HP Reverb G2.
You can either use the passive retro-reflective type markers or the active LED markers to track the HMD. Passive markers are retroreflective markers that reflect infrared light emitted from the IR LEDs on the camera. On the other hand, the active markers are LED markers that emit the IR light which gets uniquely identified in Motive. Either type of marker can be used to track HMDs. Using active marker is recommended especially for applications that involve tracking of multiple HMDs in the scene.
- Make sure the markers are attached securely and do not move. If the markers happen to move even slightly after a Rigid Body is defined, it will negatively affect the tracking and the Rigid Body definition may need to be updated.
- Avoid placing multiple markers in close vicinity as they may overlap in the camera view in certain orientations.
- Using marker posts to extend out the markers is recommended to improve marker visibility from more angles.
- If you are using the active markers, there is an extra USB port on the HMD that you could draw the power from.
Creating an HMD Rigid Body in the Builder pane.
For using OptiTrack system for VR applications, it is important that the pivot point of HMD Rigid Body gets placed at the appropriate location, which is at the root of the nose in between the eyes. When using the HMD clips, you can utilize the HMD creation tools in the Builder pane to have Motive estimate this spot and place the pivot point accordingly. It utilizes known marker configurations on the clip to precisely positions the pivot point and sets the desired orientation.
- 3.Under the Type drop-down menu, select HMD. This will bring up the options for defining an HMD Rigid Body.
- 4.If the selected marker matches one of the Active clips, it will indicate which type of Active Clip is being used.
- 5.Under the Orientation drop-down menu, select the desired orientation of the HMD. The orientation used for streaming to Unity is +Z forward and Unreal Engine is +X forward, or you can also specify the expected orientation axis on the client plugin side.
- 6.Hold the HMD at the center of the tracking volume where all of the active markers are tracked well.
- 8.Click Create. An HMD Rigid Body will be created from the selected markers and it will initiate the calibration process.
- 9.During calibration, slowly rotate the HMD to collect data samples in different orientations.
- 10.Once all necessary samples are collected, the calibrated HMD Rigid Body will be created.
This is supported only for Motive versions 2.1.2 or above. If you are using any other versions of Motive 2.1, please update the version to 2.1.2, or use a template to create the Rigid Body definition; instructions for which is provided in the following page: Using a Template File to Create Vive Pro Active Clip Rigid Body.
SteamVR Required: The VR driver streams tracking data through SteamVR. Please make sure SteamVR is installed on the computer before setting up the driver.
Download the OpenVR driver from the downloads page. Once downloaded, launch the installer and follow the prompts to set up the driver. On the last window, make sure to select Launch Configuration Utility before clicking Finish. This will open the Configuration options to setup your HMD with Motive.
You may receive a warning window prior to the installation wizard. To circumvent this, select More info and then Run Anyway.
Windows installation warning.
OptiTrack OpenVR Driver Setup Wizard Window.
Once the driver has been successfully installed, launch the configuration utility software (C:\Program Files\OptiTrack\OpenVR Driver\ConfigUtil). Using this tool, you can load and check existing configurations and make changes to the settings as needed. To import current settings, click Load and to save out the changes, click Save.
Please make sure you are running this tool with admin privileges; if not, it might not be able to modify the settings properly. If the configuration software detects a running instance of SteamVR through OpenVR, it will be indicated as Initialized at the very top as shown in the image. Please note that when the settings get modified while SteamVR is running, the SteamVR must be restarted to apply the changes.
First, configure the connection settings so that the driver listens to the Motive server where the tracking data is streamed from. The server address must match the address where Motive is streaming the data to, and the local address must match the IP address of the computer on the network where the driver is installed.
Save the configurations by clicking on Save. This will modify the set of configurations in the steamvr.settings file in the steam installation directory and they will override the HMD tracking with the tracking data from Motive. If you already had an instance of OpenVR or SteamVR running, restart the application to apply the changes.
The configuration tool basically imports and modifies the contents in the steamvr.settings file (C:\Program Files (x86)\Steam\config\steamvr.settings). When needed, the driver related settings can be changed directly from this file also, but it will be easier to configure the settings using the provided configuration tool.
Confirm the setup
Launch SteamVR. If the driver is successfully set up, you should see a tracker icon added to the right of the HMD icon and the HMD will now be using the motion capture system instead of the base stations. Here, please make sure all of the lighthouse base stations are powered off.
VIVE controllers are a Beta feature and may not work for every device. Support for this particular feature is limited.
When needed, the Vive controllers can be configured as well. To do so, open the configuration utility tool while SteamVR is running. At the top of the configuration tool, it should indicate OpenVR status as Initialized and the controllers must be showing up in SteamVR. Then, in the controller sections, enable the controllers, specify the override device using the drop-down menu, and input the corresponding streaming ID of the controller Rigid Bodies in Motive. Once everything has been configured, save the changes and restart SteamVR. When the override is configured properly, SteamVR will have an additional tracker icon per each enabled controller.
Now that the driver is set up, the HMD tracking will be overridden by tracking data from the mocap camera system, and you can integrate HMDs into the game engine through their own VR integration.
HMD Rigid Body streaming settings in Motive.
- Enable must be set to toggled on.
- Local interface must be set to the desired IP address to stream the tracking data from.
- Streaming of Rigid Bodies must be set to True
- For wireless streaming, use Unicast streaming type.
Once Motive is configured for streaming, launch SteamVR home to check the connection. If everything is setup correctly, you should be able to move around, or translate, within the scene freely. You may also need to check the ground plane to make sure it's well aligned.
If you experience any unexpected rotations in the view as you move your head, it could indicate that the HMD pivot point has not been calibrated properly. Please revisit the HMD Setup section and make sure the HMD Rigid Body pivot point is positioned and oriented at the expected pivot; which is at the root of nose with z-forward.
Make sure Unreal Engine is configured for SteamVR development. Please refer to the Unreal Engine's documentation for more information on developing for SteamVR.
This driver is designed for streaming of HMD and controller tracking data only. For streaming tracking data of other Rigid Body objects, you will need to use the corresponding plugins (UnrealEngine or Unity). In other words, the HMD tracking data will be streamed through the SteamVR using the driver you've installed, and all other tracking data will be streamed through the plugin.
When using the OpenVR driver for the HMD and the game engine plugins (UE/Unity) for other types of tracking data, including Rigid Body data, the client origin object must be located at the global origin without any rotations. In other words, the position must be set to (0,0,0) and the rotation must be set to (0,0,0) on the client origin. This is important because this will align the coordinate system from the (UE/Unity) plugin with the coordinate system in OpenVR pipeline
Notes for Unreal Engine Users
When using the Unreal Engine plugin, you will need to additionally create a custom pawn for properly aligning the coordinate systems between SteamVR and OptiTrack UE plugin:
- 2.Create a new pawn. Right-click in Content Browser, and from the context menu, select Blueprint → Blueprint Class → Pawn.
- 3.Load created Blueprint in the editor and add a camera component.
- 4.(optional) Double-check that the “Lock to HMD” property is set to true under the camera component properties in the details pane.
- 5.Select the pawn and set the “Base Eye Height” property to 0 in the details pane.
- 6.Compile the pawn then add it to the scene.
- 7.Select the pawn and set the “Auto Possess Player” to “Player 0”.
- 8.The HMD should now be working for Levels built for VR.
Configured properties of the custom pawn.
Configured properties of the added camera component.