Datasets:

josefheidler
/

har_ee_adults_2024-lendt

@@ -221,20 +221,23 @@ Accelerometer values use the **hub standard axis convention**, shared across all
 Harmonized accelerometer data is presented in a **front-thigh frame** — as if the sensor were mounted on the anterior surface of the dominant thigh. The physical sensor (Axivity AX6) was originally worn on the **lateral side of the dominant thigh** (midway between hip and knee); corrections transform the native lateral-thigh axes to the front-thigh convention.
-Native lateral-thigh axes depend on which thigh (standing upright):
-| axis | right thigh (original placement) | left thigh (original placement) |
-|------|----------------------------------|----------------------------------|
-| x    | down                             | down                             |
-| y    | right (laterally outward)        | left (laterally outward)         |
-| z    | backward                         | forward                          |
-The left-thigh z is forward (not backward) because the mirrored placement rotates the device ≈180° around the long axis, flipping y and z simultaneously.
-Correction applied to reach front-thigh (hub) frame — x=up, y=right, z=forward:
-- **Right-dominant**: negate x and z — `acc_x ← -acc_x`, `acc_z ← -acc_z`.
-- **Left-dominant**: negate x and y — `acc_x ← -acc_x`, `acc_y ← -acc_y`.
 `plucky-python` and `royal-robin` have `dominant_leg` overridden to `right` per the upstream `code/main.ipynb` correction, so they receive the right-dominant correction path.

 Harmonized accelerometer data is presented in a **front-thigh frame** — as if the sensor were mounted on the anterior surface of the dominant thigh. The physical sensor (Axivity AX6) was originally worn on the **lateral side of the dominant thigh** (midway between hip and knee); corrections transform the native lateral-thigh axes to the front-thigh convention.
+Native lateral-thigh axes, **verified from the raw sit/cycling ground truth** (median gravity per posture), standing upright:
+| axis | meaning              | right thigh | left thigh |
+|------|----------------------|-------------|------------|
+| x    | long axis            | down        | down       |
+| y    | anterior–posterior   | +y backward | +y forward |
+| z    | medio-lateral        | lateral     | lateral    |
+The anterior–posterior axis is **y** (not z), and the medio-lateral axis is **z** — the reverse of an earlier assumption that rotated the harmonized frame 90° (anterior gravity landed on −y). The y-sign is mirrored between sides because the mirrored placement rotates the device ≈180° about the long axis.
+Correction applied to reach front-thigh (hub) frame — x=up, y=right, z=forward — a proper rotation:
+- **Both**: `acc_x ← -acc_x` (long axis up).
+- **Right-dominant**: `acc_y ← -acc_z`, `acc_z ← -acc_y`.
+- **Left-dominant**: `acc_y ← acc_z`, `acc_z ← acc_y`.
+A per-subject safety normalization then enforces sitting `acc_z` positive (falling back to cycling), guarding against any mislabeled dominant leg. Verified: **every subject reads sitting acc_z positive** (and cycling acc_z positive), matching the other thigh datasets on this hub.
 `plucky-python` and `royal-robin` have `dominant_leg` overridden to `right` per the upstream `code/main.ipynb` correction, so they receive the right-dominant correction path.