looming op• 数据种类:matrix × table → table
• 调用: import fullseye as fs; fs.ledger.fly_expansion_readout(flow, lattice, axis=None, weights=None)(要直接调用实现,import flyvision; flyvision.fly_expansion_readout(flow, lattice, axis=None, weights=None);从台账取用则 opsflyvision.get("fly_expansion_readout"))
由整个眼的光流读出碰撞时间——孔径效应给出恰好 2 倍。
> 以下的详细说明为原文 —— 摘要与标题已翻译。
A fronto-parallel surface approached at speed v from distance d moves the line of sight at polar angle theta outward at sin theta cos theta / tau with tau = d/v. This op projects the measured flow onto the outward radial direction and fits that one number, 1/tau, by weighted least
squares::
1/tau = sum w f_r sin cos / sum w (sin cos)^2
and, independently, fits a linear field f = A x + b on the gnomonic plane and reads the divergence tr A, which sceneflow converts the same way (ttc = 2/div).
The reason to have both: a correlation-type detector only sees the motion component across a contrast edge. Over vertical stripes every edge is vertical, so the elevation component of the flow is lost (the aperture problem), the radial projection keeps on average half the expansion, and both readouts return 2 tau — the surface looks twice as far as it is. A checkerboard has edges in both directions and returns tau. That is the identity How et al. (2020) argued from, written as a number.
flow: (n, 2) azimuth/elevation flow per ommatidium (radians per
second), the return of fly_flow_from_directions.
lattice: the eye it was measured on (hexagonal or Vogel).
axis: the direction of travel = focus of expansion, body coordinates;
None = the lattice's optical axis.
weights: None or (n,) non-negative weights (e.g. 0 on the rim, where
fly_flow_from_directions reports nothing).
Returns a dict {"tau_s", "rate_1_s", "tau_div_s", "divergence_1_s", "aperture_ratio", "residual_rms", "n_ommatidia"} — the radial-fit time-to-contact and its rate, the divergence-fit time-to-contact and the divergence, the ratio of the smaller to the larger diagonal of A (1 for isotropic expansion, 0 under a pure aperture effect), the rms of the radial residual and how many ommatidia voted. A non-expanding field (rate <= 0) returns NaN for the time-to-contact — a documented non-finite, as in fly_tau_from_expansion: a receding surface has no time-to-contact.
Ground truth (pinned in the tests): the exact plane flow returns tau_s == tau and tau_div_s == tau to 1e-9 (the divergence is fitted on gnomonic velocities, where a plane approach is exactly linear); the same flow with its elevation component removed returns 2 tau from both readouts within 1% on a 10-degree field (aperture_ratio 0) — a hexagonal lattice is 6-fold symmetric, so sum cos^2 phi = sum sin^2 phi over it, and the residual is the sphere's departure from that plane.
Raises ValueError: a *flow* that is not (n, 2) for this lattice (an empty *flow* is refused), non-finite entries, a malformed *lattice* / *axis* / *weights*, all-zero weights, and fewer than 6 voting ommatidia.
• 示例数据目录(下载 URL / 许可证) —— 2-D 用 skimage.data(BSD/公有领域)加合成图,3-D 给出真实数据源(Stanford/PDS 等)的下载 URL。
• 算子来历与参考文献 —— 该算子族所依据的研究/方法出处。
• 算法的正典(作者、年份)与用途见上面的族使用指南。
• poc_zebra_stripes_fly_eye — py -3.11 examples/poc_zebra_stripes_fly_eye.py
table 作为输入)fly_t4t5_field · fly_flow_from_directions · fly_matched_filter · fly_egomotion_from_flow · fly_eye_merge · fly_view_plane_texture · fly_hex_resample · lattice_moire_peak
looming)fly_lgmd_eta · fly_tau_from_expansion
*Provenance: flyvision.py — FLYVISION 算子登记表。本条目由 tools/opdocs.py md 自动生成(请勿手工编辑)。*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.