When to use

Use this skill when you need to compute any of:

•Whole-body COM (and COM velocity) from C3D marker trajectories
•XCoM / eXtrapolated Center of Mass (Hof inverted-pendulum)
•Foot-landmark-based BoS polygon (single or double support) without force plates
•Signed MoS/MOS as the shortest distance from XCoM to the BoS boundary

This skill is designed to work with the marker-set guidance from:

•motive-marker-v3d-guideline

Hard requirements (ask the user if missing)

Before running code, confirm you have:

•C3D file(s)
•
Subject anthropometrics (minimum)
- •leg length
- •foot length
- •foot width
- •ankle width
- •knee width
•
Event info (choose one)
- •perturb_inform.xlsm (recommended)
- •OR explicit platform onset/offset + step onset frames

If anthropometrics are not provided, you must request them. This project requires anthropometrics to generate BoS landmarks and XCoM.

Outputs

Typical outputs per trial:

•*_COM.csv (COM position)
•*_XCOM.csv (XCoM position)
•*_BOS_vertices.csv (BoS hull vertices per frame)
•*_MOS.csv (signed MoS time series)
•Optional: *_COM_validation.txt (correlation vs V3D COM export)

Visual3D-equivalent method (conceptual)

Mirror the canonical V3D tutorial logic:

•COM and COM velocity from a kinematic model (or a validated proxy)
•XCoM computed from COM and COM velocity using Hof’s inverted-pendulum scaling
•BoS derived from foot landmarks (measured or virtual) to form a polygon (single/double support)
•MoS as the shortest distance from XCoM to the BoS boundary (signed)

See references:

•references/v3d-logic-summary.md
•references/anthropometrics.md

Scripted pipeline (recommended)

Quick start (single trial)

bash

python scripts/run_mos_pipeline.py \
  --c3d /path/to/251112_KUO_perturb_60_001.c3d \
  --events /path/to/perturb_inform.xlsm \
  --subject "김우연" \
  --out_dir ./outputs \
  --anthro ./assets/example_anthro_kimwooyeon.yaml \
  --v3d_com_ref /path/to/251112_KUO_perturb_60_001_COM.xlsx

Batch mode (folder)

bash

python scripts/run_mos_pipeline.py \
  --c3d_dir /path/to/c3d_folder \
  --events /path/to/perturb_inform.xlsm \
  --subject "김우연" \
  --out_dir ./outputs \
  --anthro ./assets/example_anthro_kimwooyeon.yaml

Implementation notes

•The pipeline assumes C3D marker trajectories are already labeled/filtered.
•No force plate is required; if force channels exist, they are ignored.
•Coordinate axes can vary; the script allows configuring the vertical axis and ground plane.