[Stay Aligned] Add small yaw rotations to keep trackers aligned #508

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MrUnknownDE · 2026-04-05T19:22:42+02:00

MrUnknownDE commented

2026-04-05 19:22:42 +02:00

Originally created by @jabberrock on 2/2/2025

Add small yaw rotations to keep trackers aligned. Stay Aligned applies small yaw corrects every server tick. It can successfully keep the user aligned in many poses including standing, sitting and lying down.

This feature has two primary ideas:

If the player is not moving, the tracker yaws should not be changing.
If the player is moving, on average, the player will be in their relaxed pose.

Every server tick, Stay Aligned picked a tracker, calculates an error based on 3 forces (locked trackers, centering force, and neighbor trackers), and uses gradient descent to nudge the tracker's yaw.

Main classes:

StayAligned: Entry point of Stay Aligned that is called from HumanSkeleton
AdjustTrackerYaw: Performs the gradient descent
LockedErrorVisitor, CenterErrorVisitor and NeighborErrorVisitor calculates the errors for gradient descent
StayAlignedTrackerState: Tracks the Stay Aligned state per tracker

Supporting classes:

TrackerSkeleton: Visits trackers, while providing neighboring trackers
TrackerPose and TrackerSkeletonPose: Detects the pose of the player from tracker orientations
RestDetector: Detects when a tracker is at rest

TODO: For the actual release, we should make a wizard for detecting the relaxed body angles.

https://github.com/SlimeVR/SolarXR-Protocol/pull/157

*Originally created by @jabberrock on 2/2/2025* Add small yaw rotations to keep trackers aligned. Stay Aligned applies small yaw corrects every server tick. It can successfully keep the user aligned in many poses including standing, sitting and lying down. This feature has two primary ideas: 1. If the player is not moving, the tracker yaws should not be changing. 2. If the player is moving, on average, the player will be in their relaxed pose. Every server tick, Stay Aligned picked a tracker, calculates an error based on 3 forces (locked trackers, centering force, and neighbor trackers), and uses gradient descent to nudge the tracker's yaw. Main classes: 1. `StayAligned`: Entry point of Stay Aligned that is called from `HumanSkeleton` 2. `AdjustTrackerYaw`: Performs the gradient descent 3. `LockedErrorVisitor`, `CenterErrorVisitor` and `NeighborErrorVisitor` calculates the errors for gradient descent 4. `StayAlignedTrackerState`: Tracks the Stay Aligned state per tracker Supporting classes: 1. `TrackerSkeleton`: Visits trackers, while providing neighboring trackers 2. `TrackerPose` and `TrackerSkeletonPose`: Detects the pose of the player from tracker orientations 3. `RestDetector`: Detects when a tracker is at rest ![image](https://github.com/user-attachments/assets/b35c4c14-cca7-4208-8e4d-5ad6b3f95184) ![image](https://github.com/user-attachments/assets/1ffecb31-08c4-48da-9afc-11f671afaadf) TODO: For the actual release, we should make a wizard for detecting the relaxed body angles. https://github.com/SlimeVR/SolarXR-Protocol/pull/157

MrUnknownDE closed this issue

2026-04-05 19:22:42 +02:00

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Reference: github/SlimeVR-Server#508