Fix Mean Saccade Velocity Calculation Denominator

[oscararenas12]

Summary

Fixes mean saccade velocity calculation bug in SaccadeVelocity.java.

Problem

The denominator incorrectly used saccadePoints.size() - discardedDataCount, which divides by the number of points instead of the number of velocity measurements.

Solution

Changed line 226 to saccadePoints.size() - 1 - discardedDataCount because n points produce n-1 velocity
measurements between consecutive points.

Example

With 5 points and 1 discarded measurement:

• Old (incorrect): 5 - 1 = 4
• New (correct): 5 - 1 - 1 = 3

Changes

• Updated getMeanVelocity() denominator calculation
• Added JavaDoc explaining n points produce n-1 velocities
• Updated test_DGMs.csv to correct velocity values

Needed

We must update User Manuel, section 4.2.3.1 "Saccade Velocity" (page 17) says:

• "Mean saccade velocity is the average speed during a saccade, calculated by summing up all velocities during a saccade and dividing by the total amount of points."

This is incorrect and needs to be updated. Based on the bug fix we just made, it should say:

• Suggested correction: "Mean saccade velocity is the average speed during a saccade, calculated by summing up all velocities during a saccade and dividing by the total number of velocity measurements (which is one less than the total amount of points, since n points produce n-1 velocities between consecutive points), excluding any measurements that exceed the velocity threshold."
  Or more concisely:
• "Mean saccade velocity is the average speed during a saccade, calculated by summing up all valid velocities during a saccade and dividing by the number of valid velocity measurements computed between consecutive points."