S8 — Zero-Velocity Update (optional)

An optional robustness layer: when the platform is detected to be stationary, apply a v = 0 pseudo-measurement (and suppress clone insertion while still). This prevents the spurious motion and feature-starved drift that otherwise accumulate when the camera sees nothing new.

What it does

Detect stationarity (low IMU specific-force/gyro variance + low visual disparity), then apply a zero-velocity pseudo-measurement that pins v = 0, and pause cloning until motion resumes.

The contract

Signature	detect stationarity (IMU + visual disparity) → apply a v = 0 pseudo-measurement; suppress clone insertion while still
Post / invariants	prevents spurious motion / feature-starved drift while static · the detector must not false-positive during slow motion (a wrong v = 0 constraint injects a bias)
cortex	not present — a known canonical robustness layer

Status — optional, not implemented

Zero-velocity updates are not present in the cortex filter. They are a deployment-robustness feature (most valuable for ground vehicles and hand-held/stop-and-go motion), and are not relevant to the EuRoC #212 over-confidence, which is measured on continuously-moving sequences. The main design caution is detector precision: a false-positive during slow motion injects a wrong v = 0 constraint and biases the estimate.