4. Zero-Angle Definitions

4.1. Why We Use a Custom Zero-Angle Model

In our platform, we use a unified zero-angle definition for exercise and health analysis. Instead of treating anatomical resting positions as non-zero values (for example, elbow at about 180 in relaxed standing), we normalize each joint so the relaxed baseline is treated as 0.

This means every tracked joint starts from a common reference point. The result is a cleaner and more intuitive model for developers, coaches, and clinicians who need to compare movement quality across different joints, cameras, and scenarios.

Why This Helps in Practice

• A single interpretation model: zero always means relaxed baseline for that joint in that scenario.
• Easier threshold design: movement rules can be defined around offsets from baseline instead of mixed absolute angle conventions.
• Better cross-joint consistency: shoulder, elbow, hip, and knee can be reasoned about in a unified way.
• More readable reports: progress and posture deviation become simpler to explain to non-technical users.

What Comes Next

The next three pages document the camera-specific zero-angle tables: Front, Right, and Left. These tables define which baseline is considered zero for each joint in each capture scenario.