Recording requirements¶

STRIDE was validated on three rigs filming the same 10 cm corridor T-maze. The numbers below are what separated usable gait from unusable gait; cognitive scoring is far less demanding.

Requirement	Gait	T-maze decisions
Paws visible	yes: camera below a transparent floor	not needed
Scale on the floor	20 px/cm or more	any resolution where the regions are visible
Frame rate	100 fps or more	30 fps and up
Direction	the maze stem (or the walking direction) runs left to right in the image	any
Compression	low, global shutter preferred	not critical
Scale reference	a ChArUco board in view, or a px/cm you measured	not required

The rig checker on the project page reads a video in the browser and reports whether a set-up meets these (Web tools).

What STRIDE does when a recording does not meet them¶

It warns, and it never changes a value:

below 100 fps or below 20 px/cm the gait step prints a warning and still writes the tables;
when the maze stem (stride tmaze) or the body axis while walking (stride gait) does not run along the image x-axis it prints a warning. The step and stride measures and the forward-direction filter assume that direction; STRIDE does not correct for it (Stride detection and gait measures);
the lens distortion check is a report only. STRIDE does not undistort.

Why these numbers¶

Scale. At 10 px/cm a paw is a 3-pixel blob, and stride length and body length pick up systematic artefacts. The gait of the paper's 1024 x 1024 industrial-camera batch was excluded for that reason; its T-maze decisions were kept.
Frame rate. Swing phases are short (10th percentile about 60 ms). A swing must span at least 3 frames to be detected and 5 frames to be measured well. At 120 fps 97% of swings clear the 5-frame bar; at 60 fps 27% are lost; at 30 fps gait cannot be resolved.
Compression. Heavy H.265 compression raised the tracking noise floor of a 4K action camera to about 2 mm, against 0.2 mm for a less compressed 4K camera at the same scale. Sway metrics of a few millimetres need the lower floor.

Scale reference¶

stride calibrate, and the calibrate step of both pipelines, measure px/cm from a ChArUco board lying in view of the camera (default 14 x 9 squares, 20 mm squares, 15 mm markers, DICT_5X5_250). The board must lie flat in the plane the animal walks on and be visible during the first 10 s of at least three clips. Details: Scale calibration.

Without a board, give the scale yourself (--px-per-cm). stride tmaze can also fall back on the corridor width of each video's ROI; stride gait has no such fallback and stops.

File names¶

stride tmaze and stride gait accept any video file names; they only have to be unique within a run, because every table is keyed by the file name.

Names of the form Day<N>_<mouse>_Trial<T>.mp4 are recognised: day, mouse and trial are then filled from the name. The stage-by-stage batch runner (run_all.py, stride analyze-decisions, stride run) requires that form and a reward table (Stage-by-stage batch runs).