Methodology & Physics
The L3S Sail Analyzer uses computer vision and geometric analysis to quantify sail shape. This page explains how each metric is calculated to ensure transparency and trust in the data.
1. Coordinate System
Every analysis begins by defining a Chord Line connecting the luff (front) to the leech (back) of the sail stripe.
- Chord (C): The straight line distance between the start point (P1) and end point (P2).
- Rotation: The entire stripe path is rotated so that the Chord Line becomes the X-axis (y=0).
- Normalization: All measurements are relative to the Chord Length (C), allowing comparison between different photos/zoom levels.
2. Camber
Camber represents the maximum depth of the sail profile.
We scan every point on the stripe. The point with the greatest perpendicular distance from the Chord Line is the Max Depth.
3. Draft Position
This metric tells you where the maximum depth occurs along the chord.
A value of 40% means the deepest part of the sail is 40% of the way back from the luff.
4. Twist
Twist measures the angle of the stripe relative to the horizontal plane (or camera frame).
Note: Absolute twist requires a reference (boom or true horizontal). In this analyzer, it is relative to the image frame. For accurate comparison,ensure the camera angle remains constant between shots.
5. Entry & Exit Angles
These angles define the aerodynamic attack and release of the airflow.
- Entry Angle: Calculated by fitting a tangent line to the first 0-15% of the stripe.
- Exit Angle: Calculated by fitting a tangent line to the last 85-100% of the stripe.