Issue with CoG Velocity Calculation: Units and Near-Zero Results

[Vincent-Crawl]

Have I written custom code (as opposed to using a stock example script provided in MediaPipe)

Yes

OS Platform and Distribution

Windows 10 Home Basic 64 - bit

MediaPipe Tasks SDK version

0.10.20

Task name (e.g. Image classification, Gesture recognition etc.)

Pose Estimation

Programming Language and version (e.g. C++, Python, Java)

Python

Describe the actual behavior

The calculated CoG velocity is consistently near zero, even though the CoG position changes visibly in the video. This suggests a unit conversion issue or a problem with the calculation method.

Describe the expected behaviour

The CoG velocity should reflect the actual movement speed of the body's center of gravity, expressed in meters per second (m/s).

Standalone code/steps you may have used to try to get what you need

import cv2 import mediapipe as mp import numpy as np from scipy.signal import savgol_filter # ... (MediaPipe initialization and video capture) CoG_positions = [] while cap.isOpened(): # ... (MediaPipe pose processing) if results.pose_landmarks: landmarks = results.pose_landmarks.landmark CoG_x_pixel, CoG_y_pixel, CoG_z_pixel = calculate_body_center(landmarks) # Your CoG calculation function CoG_positions.append([CoG_x_pixel, CoG_y_pixel, CoG_z_pixel]) # ... (after the loop) CoG_positions = np.array(CoG_positions) # Velocity calculation (this is where I suspect the problem lies) CoG_velocities = np.diff(CoG_positions, axis=0) * fps # ... (smoothing and plotting)

Other info / Complete Logs

Here's an example of CoG position and velocity values:

Frame 1: CoG Position (x, y, z) = (0.3437, 0.7112, -0.0171)
Frame 1: CoG Velocity (x, y, z) = (0.0823, -0.3564, -0.1760) (These values are likely incorrect due to units.)
I suspect the issue is that the MediaPipe 3D coordinates are not in meters.  Could you please clarify the units and how to convert them to meters for velocity calculation?  Are there best practices for calculating CoG velocity with MediaPipe?

[kuaashish]

Hi @Vincent-Crawl,

Please provide the complete standalone code to help us understand and reproduce the issue if needed. Alternatively, you can share the documentation you are following along with details of the support you require from us.

Thank you!!