Knowledge Base

Problem

After retracking a pre-recorded video in EthoVision XT, the 'Distance Moved Total' and 'Velocity Mean' values appear nearly identical or unexpectedly similar, whereas the original live-acquired file showed clearly different values for these two parameters.

Details

Occurs when retracked data is analyzed in 1-second time bins. Because velocity is calculated as distance divided by time, and the bin duration is 1 second, the two values will be numerically close or equal. This is not a tracking or calculation error but an artifact of the analysis interval selected. Affects users comparing live-acquired and retracked versions of the same experiment.

Solution

1. Understand that this is expected behavior: when data are analyzed in 1-second bins, Distance Moved (cm) and Velocity Mean (cm/s) will be nearly identical because velocity = distance ÷ ~1 second.
2. To distinguish the two parameters meaningfully, increase the analysis interval bin size (e.g., use 5-, 10-, or 60-second bins). Over longer intervals, total distance and mean velocity will diverge as expected.
3. Alternatively, export raw sample data and calculate statistics manually over the desired interval.
4. If you need the overall trial mean velocity to differ from total distance, ensure your analysis interval spans the full trial duration rather than 1-second sub-intervals.