Lighthouse trackers, controllers and base stations aligned to a Quest Pro's own tracking, continuously, with nothing mounted on the headset. The Quest Pro's tracking cameras see the laser flashes of SteamVR 2.0 base stations. Each flash is a bearing from the headset to a base station. From those bearings QuestLHSync works out where the lighthouse space sits in the Quest's space and keeps correcting it while you play. Full-body trackers and Index controllers then line up with a streamed Quest Pro without SpaceCalibrator or a tracker strapped to your head.

It has two parts:

• A Magisk module for the headset. It serves what the tracking cameras see of the base stations on your local network.
• A SteamVR driver for the PC. It solves the alignment and applies it to every lighthouse device. It also adds a page to the SteamVR dashboard.

• A Quest Pro, rooted with Magisk. Other Quests have tracking cameras too and could work, but it has only been tried on a Quest Pro.
• SteamVR 2.0 base stations. 1.0 stations aren't supported.
• Windows with SteamVR, and the Quest Pro streamed to it by anything: Link, Air Link, Virtual Desktop, ALVR, Steam Link, CreoleCast and so on.
• The PC and the headset on the same local network.
• At least one lighthouse device switched on, such as a tracker or an Index controller. SteamVR only shows base stations while one is on.

1. Download QuestLHSync-<version>.zip from Releases and extract it.

2. Headset: install QuestLHSync-magisk-<version>.zip in the Magisk app (Modules > Install from storage) and reboot. To install it over adb instead:

   adb push QuestLHSync-magisk-v1.1.zip /sdcard/Download/
   adb shell su -c "magisk --install-module /sdcard/Download/QuestLHSync-magisk-v1.1.zip"
   

3. PC: with SteamVR closed, move the questlhsync folder somewhere permanent and register it (adjust the paths):

   "C:\Program Files (x86)\Steam\steamapps\common\SteamVR\bin\win64\vrpathreg.exe" adddriver "C:\path\to\questlhsync"
   

4. Turn off any other tool that moves lighthouse devices into the Quest's space, such as SpaceCalibrator or OpenVR-SpaceSync. Two tools correcting the same devices fight each other.

Start SteamVR the way you usually do. QuestLHSync finds the headset on the network by itself. Its page is in the SteamVR dashboard, and a copy opens on the desktop. Closing the desktop window hides it until the next SteamVR start.

The first time, look around the room so the side cameras catch both base stations. It locks within about half a minute, usually sooner. After that it starts from the saved alignment as soon as the base stations appear.

The page shows the headset link, each base station's sightings and the alignment's median error. Recent log lines are at the bottom. The buttons:

• Re-acquire drops the sightings so far and finds the alignment again from new ones. Use it if lighthouse devices look out of place.
• Pause corrections keeps lighthouse devices where they are until you resume.
• Record session saves everything the driver receives to a file, for bug reports. It's off unless you turn it on.

• Headset. lhsyncd answers discovery on UDP 47281 and serves one TCP stream per PC on port 47280. Only while a PC is connected, it runs a small Frida script inside the sensors HAL (vendor.oculus.hardware.sensors@1.0-service). The script reads the two side tracking cameras' frame buffers, never writes to them, and reports saturated spots in the short-exposure frames. The front cameras are skipped: they never saw a base station in testing, only other lights. It stops a few seconds after the last PC leaves. Nothing on disk is patched and no partition is touched. The camera calibration is read from /persist/calibration and sent to the PC with the stream.
• Alignment. Each spot becomes a ray from the camera, placed at the headset's SteamVR pose at the moment of exposure, and is matched to the nearest base station. Both spaces share gravity, so the fit has 4 degrees of freedom: yaw and a translation. It uses a robust least-squares fit over the last few minutes of sightings, with outliers rejected.
• Applying it. The driver hooks IVRServerDriverHost::TrackedDevicePoseUpdated with MinHook. Every device whose tracking system is lighthouse gets the transform. The HMD is left alone. Corrections are eased in while your head moves, so lighthouse devices don't visibly slide.
• Timing. Streamers report head poses with different delays. QuestLHSync learns the offset between the camera frames and the head pose for each streamer, from how the error grows with head speed, and remembers it.
• Reference frame. SteamVR re-levels its lighthouse space at every start. QuestLHSync pins its own reference frame to one base station, the anchor, so a saved alignment stays valid across restarts.

Optional, in steamvr.vrsettings under "driver_questlhsync":

The PC side writes only to %LOCALAPPDATA%\QuestLHSync:

Nothing is sent anywhere except between the PC and the headset. The PC only makes outgoing connections, so Windows Firewall needs no rule.

While a PC is connected, scanning the cameras takes about 3% of one of the headset's CPU cores, and the stream is about 2.5 KB/s. On the PC, the solver uses about 0.2% of one core.

On the headset, lhsyncd answers anyone on the local network. The stream has no authentication. It carries the spots' pixel positions (never images), the camera calibration, and the headset's serial number, model and firmware version. Use it on a network you trust. Frida's temporary files go to a RAM folder, /dev/.questlhsync.

• "Looking for the headset": the headset must be awake and on the same network. Some routers isolate Wi-Fi clients or drop broadcasts: set host to the headset's IP address.
• "No camera frames": the cameras only run while the headset is tracking. Put it on.
• "Waiting for base stations": switch on a tracker or controller.
• "Finding the base stations" for a long time: both base stations need to be seen. Face each of them for a few seconds.

• Headset: remove the module in the Magisk app and reboot.
• PC: with SteamVR closed, run vrpathreg removedriver "C:\path\to\questlhsync", then delete %LOCALAPPDATA%\QuestLHSync.

QuestLHSync finds the camera buffers in the sensors HAL by their sizes and the order they were allocated in. It was developed on one Quest Pro and one OS build. Another OS build may lay them out differently. If it does, the page stays on "No camera frames" and nothing else on the headset is affected. Frida is pinned to 17.10.0, because 17.19.0 crashed the sensors HAL on injection.

Visual Studio 2022 with C++, the Android NDK (r28c tested) and Python 3:

build.bat                        SteamVR driver + dashboard app, into driver\questlhsync (SteamVR closed)
python magisk\build_module.py    Magisk module, into out\ (downloads frida-inject once)
python release.py                out\QuestLHSync-<version>.zip
python install.py                register driver\questlhsync with SteamVR, in place
python install.py headset        install the module over adb and start it without a reboot

build_replay.bat builds two test tools. qlhs_replay runs a recording through the solver offline. qlhs_nettest runs the network link and the solver against src\tools\fake_lhsyncd.py, which replays a recording as a fake headset.

MIT, see LICENSE. Third-party code is listed in THIRD_PARTY_NOTICES.md.

QuestLHSync is not affiliated with Meta or Valve. Meta Quest is a trademark of Meta Platforms, Inc.; SteamVR is a trademark of Valve Corporation. Rooting a headset and running code inside its system services is at your own risk.