looming op• Data kinds: signal → signal
• Call: import fullseye as fs; fs.ledger.fly_tau_from_expansion(theta_signal, dt_s, shape='sphere') (to call the implementation directly, import flyvision; flyvision.fly_tau_from_expansion(theta_signal, dt_s, shape='sphere'); from the registry, opsflyvision.get("fly_tau_from_expansion"))
Time-to-contact from optical expansion — the tau margin.
From the subtended angle and its rate::
shape="disk": tau = sin(theta) / theta'
shape="sphere": tau = 2*tan(theta/2) / theta'
theta_signal is the full subtended angle over time, radians.
★ The two object models differ by 33% at a 60-degree subtense (sin 60 = 0.866 vs 2 tan 30 = 1.155); using the wrong one silently mis-times a landing, so the model is a required, named choice rather than a default guess.
theta_signal: the full subtended angle per sample, radians.
dt_s: the sample interval, seconds.
shape: "disk" (a frontal circular disk) or "sphere".
Returns a 1-D float64 array of the time-to-contact per sample, seconds. Non-expanding samples (theta' <= 0) return NaN — a documented non-finite, because a contracting or static angle has no time-to-contact and inventing one would be a plausible-wrong number. (The registry op tb_fly_tau_from_expansion must return a finite signal, so it replaces those NaN by the signal fallback without recording a fallback event — backend_safe.NONFINITE_BY_DESIGN; call this function directly to keep the NaN.)
Ground truth: for the model's own object geometry (theta = 2 asin(l/d) for a sphere, theta = 2 atan(l/d) for a disk) approaching at speed |v|, the returned tau equals the true distance-over-speed d/|v| (pinned in the tests).
Raises ValueError: a non-1-D / empty / too-short (< 3) / non-finite *theta_signal*, a signal over MAX_SIGNAL_POINTS, a non-positive *dt_s*, and an unknown *shape*. A non-expanding angle is not an error — it is the documented NaN return above.
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
• poc_fly_vision — py -3.11 examples/poc_fly_vision.py
signal as input)fly_hex_quantize · fly_emd_response · fly_lgmd_eta · fly_dsi
looming)*Provenance: flyvision.py — FLYVISION operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.