fly_tau_from_expansion — FLYVISION `looming` op

• データ種: signal → signal

• 呼び出し: import fullseye as fs; fs.ledger.fly_tau_from_expansion(theta_signal, dt_s, shape='sphere') (実装を直接呼ぶなら import flyvision; flyvision.fly_tau_from_expansion(theta_signal, dt_s, shape='sphere')、台帳から引くなら opsflyvision.get("fly_tau_from_expansion"))

使い方

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.

詳しい使い方ガイド

• fly_vision ファミリガイド

参考(サンプルデータ・文献)

• サンプルデータカタログ(DL URL / ライセンス) — 2-D は skimage.data(BSD/public)+ 合成、3-D は実データ源(Stanford/PDS 等)の DL URL。

• 演算子の来歴・参考文献 — この op 族の元になった研究/手法の出典。

• アルゴリズムの正典(著者・年)と用途は上記ファミリ使い方ガイドに記載。

実行できる例(この op を実際に呼ぶ検証済みサンプル)

• poc_fly_vision — py -3.11 examples/poc_fly_vision.py

型が繋がる次の op(`signal` を入力に取れる)

fly_hex_quantize · fly_emd_response · fly_lgmd_eta · fly_dsi

同カテゴリ(`looming`)

fly_lgmd_eta

*Provenance: flyvision.py — FLYVISION operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。*

fly_tau_from_expansion — FLYVISION looming op

使い方