alias op• Data kinds: none → table (an op determined by its arguments alone — it takes no image or data input)
• Call: import fullseye as fs; fs.ledger.sampling_alias_distance(period_m, pitch_deg, lattice='hex', view_angle_deg=0.0, acceptance_deg=0.0, obliquity='along') (to call the implementation directly, import flyvision; flyvision.sampling_alias_distance(period_m, pitch_deg, lattice='hex', view_angle_deg=0.0, acceptance_deg=0.0, obliquity='along'); from the registry, opsflyvision.get("sampling_alias_distance"))
The distance beyond which a periodic target aliases on a sampling lattice.
A period *period_m* seen from distance d at viewing angle theta has the angular period P cos^2(theta)/d (the cos^2 is the derivative of the line-of-sight intercept; obliquity="across" — the period runs perpendicular to the plane of obliquity — makes it a single cos). A lattice of pitch *pitch_deg* resolves angular periods down to sqrt(3) * pitch (hexagonal: the inscribed circle of its Brillouin zone) or 2 * pitch (square), so the target aliases once::
d > period_m * cos^2(theta) / (sqrt(3) * pitch) (hex)
d > period_m * cos^2(theta) / (2 * pitch) (square)
The same number is the working-distance rule of an inspection camera:
*pitch_deg* is the pixel's instantaneous field of view, *period_m* the pitch of the display, mesh, weave or halftone being inspected, and beyond the returned distance the picture carries a moire that is not in the part (Petersen & Middleton 1962 for the lattice Nyquist regions).
period_m: the target's spatial period, metres.
pitch_deg: the sample spacing — inter-ommatidial angle or pixel IFOV, degrees.
lattice: one of SAMPLING_LATTICES.
view_angle_deg: the obliquity of the line of sight, |theta| < 90.
acceptance_deg: the FWHM of the Gaussian acceptance (or pixel blur), degrees;
0 means a delta sampler.
obliquity: one of OBLIQUITIES.
Returns a dict {"distance_m", "nyquist_cycles_per_rad", "period_floor_deg", "mtf_at_nyquist", "lattice", "view_angle_deg"} — the alias distance, the lattice's Nyquist frequency, the smallest angular period it resolves, and the acceptance's modulation transfer at that limit (1.0 for a delta sampler).
Ground truth (pinned in the tests): a 7 cm period on a 1.1-degree hexagonal eye aliases beyond 2.105 m head-on and 0.526 m at 60 degrees; on a 4.63-degree eye beyond 0.500 m and 0.125 m; with a 1-degree acceptance the hexagonal 1.1-degree eye keeps 0.375 of the contrast at Nyquist, the 8.23-degree acceptance of a 4.63-degree eye keeps 0.024.
Raises ValueError: a non-positive *period_m* / *pitch_deg* (an empty *period_m* is refused as not a number), a negative *acceptance_deg*, a *view_angle_deg* at or beyond 90, and an unknown *lattice* / *obliquity*.
• 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_zebra_stripes_fly_eye — py -3.11 examples/poc_zebra_stripes_fly_eye.py
table as input)fly_t4t5_field · fly_flow_from_directions · fly_matched_filter · fly_egomotion_from_flow · fly_eye_merge · fly_view_plane_texture · fly_hex_resample · fly_expansion_readout
alias)*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.