This article describes how to synchronize an OptiTrack Motion Capture system with an HTC Vive virtual reality headset system to avoid IR tracking lights from both systems do not overla. Currently, only OptiTrack Prime-series camera systems have been tested.
The HTC Vive system uses infrared LEDs and lasers for tracking their head mounted display (HMD) and controllers. When using an OptiTrack mocap system in conjunction with the HTC Vive system, the infrared tracking from the two systems may interfere with each other. For this reason, the two systems must be synchronized in a way so that the two different tracking lights do not temporally overlap. Let’s go through the synchronization setup. The following setup instructions assume that the two tracking base stations of the HTC Vive system are set to channel b and c and are optically synchronized. The channel b base station will serve as the master device for synchronizing the two systems. Sync out signal from the channel b station will feed into one of the input ports on the eSync, and a sync offset (specified in microseconds, or μs) will be applied to so that IR lights from the two systems don’t interfere with each other. The following section describes the instructions in detail.
Step 1: Set up the HTC Vive system.
The base stations will synchronize optically in this setup. Refer to the respective documentation for more details on setting up the HTC Vive system. Set the tracking stations to channels b and c, so that they are optically synchronized (in the absence of a sync cable connection between them).
Step 2: Set up Set up the OptiTrack mocap system.
Refer to the Hardware Setup wiki pages for more details.
Step 3: Connect the sync output from the channel b base station into the input port 1 of the eSync synchronization hub.
Step 4: Motive: Synchronization pane. Configure the synchronization in Motive.
Open the Synchronization pane in Motive, and set the synchronization type to Custom Synchronization.
Step 5: Motive: Synchronization pane. Configure the Sync Input.
Set the Sync Input to Input 1, which was the input port of the eSync where the sync cable was connected to. If the sync cable is properly connected and the HTC Vive system is properly working, the bottom signal monitor will display a frequency of approximately 60 Hz detected through the Input 1 port of the eSync. Note that this configuration will synchronize the OptiTrack camera system to the sync signal coming through the Input port.
Step 6: Motive: Synchronization pane. Introduce Sync Offset (μs).
Now that the OptiTrack system’s shutter timing is synchronized with the base stations of the HTC Vive system, you will need to introduce a sync offset to avoid overlapping of the tracking lights. The following list of offset sync parameters are tested to avoid the interference. Input these parameters into the Synchronization pane. If you wish to increase the final frame rate of the mocap system, you will need to apply a multiplier.
Final Frame Rate: 60 Hz
Sync Multiplier: 1
Sync Offset: 3458 μs
Final Frame Rate: 120 Hz
Sync Multiplier: 2
Sync Offset: 16114 μs
Step 7: Motive: Synchronization pane. Apply sync configuration.
Press Apply to employ the sync configuration. The tracking IR lights from both systems will no longer interfere, and the HTC Vive components will be working properly and available in the SteamVR application.
Step 8: Motive: Cameras pane. Lower the camera exposure on the OptiTrack system.
Another important note is that high camera exposure settings may cause IR light from the base stations to be detected by the OptiTrack system. If you configured the synchronization so that the final frame rate is 60 Hz, set the camera exposure setting to no higher than 1216 μs. If you configured the final frame rate to be 120 Hz, set the camera exposure setting to no higher than 904 μs.
Maximum Camera Exposure: 1216 μs
Maximum Camera Exposure: 904 μs
Now that the two systems are synchronized to avoid the IR interference, both systems can be used together to provide immersive VR experiences. Note that the instructions listed in this page are tested to work with HTC Vive system, but alternative approaches may also be possible.