CKey locator format v0.11.0 (draft)

Status: experimental reference format. The emitted locator frame has format=11 (0B) and profile=1. Format 8 remains a historical decoder-compatibility format; it is not emitted by this revision.

Geometry

The canonical field is 29 by 29 units with origin at the upper-left and centre (14.5,14.5). A rounded-square structural border runs from (0.5,0.5) to (28.5,28.5), radius 3.5, width 0.65. Coordinates are shared by renderer and decoder; colour is decorative only.

Each corner finder is an inset, edge-oriented three-arc set, not a border-sized leaf. In local top-left coordinates its centre is (2.75,2.75). The three circular centerline radii are 1.45, 2.20, and 2.95; all have width 0.42 and rounded caps. Top-right, bottom-right, and bottom-left are exact reflections and each has three continuous quarter arcs. The top-left finder has the same three arcs, but every arc is divided at the 45-degree diagonal with a 0.85-unit visible clear gap (including cap compensation). This split is the orientation signature. The physical 6 by 6 corner envelope remains non-payload, so data never touches a finder.

The polar field remains four dot rings at radii 3.6 + .8r, r=0...3, and a separate ray band from radius 7.6 to 9.5. There are 72 equally-spaced angular slots, clockwise from 12:00. The Grid Key is a 2 by 2 Cartesian block at rows 11--12 / columns 2--3. Ray Key slots 0, 54, 55 have lengths 100%, 50%, 75%. The outer ring's Ring Key is dots at slots 18,19,21; empty at 20; and one round-capped connected arc in slots 22--25. Ring dots and arc width are 0.30; the arc's visible length is exactly four slots. These structures are reserved.

Framing and placement

The payload is exactly 16 bytes. Frame bytes are C7 4B 0B 01 00 10, payload, then CRC-32C over bytes 0--21. The 26-byte frame is systematic shortened RS(77,26) over GF(256), primitive polynomial 0x11D, primitive element 2, roots alpha^0...alpha^50, high-degree-first coefficients, with 51 appended parity bytes. It corrects up to 25 unknown byte errors. CRC-32C is separate integrity detection, not error correction.

The 616 codeword bits are placed MSB-first by the same alternating Cartesian/polar sequence specified in v0.8.0: Cartesian sites are angularly interleaved; all 69 data ray slots precede round-robin inner ring sites. A light mark represents one. The Grid, Ray, Ring, boundary, finders, and center radius 10.4 are reserved. The central region inside radius 3.3 is logo-safe; no logo may overwrite a structural, payload, or parity site.

Reader requirements

An image reader rectifies a caller-supplied cyclic quadrilateral, normalizes monochrome polarity from the permanent keys, and must require Grid/Ray/Ring evidence, RS correction, and CRC-32C. The inset finder arcs are included as continuous localization evidence; the top-left diagonal clear gaps contribute orientation evidence. Candidate acceptance remains cryptographically grounded in framing/CRC and mathematically grounded in RS, rather than in visual finder matching alone. Full-frame localization and physical robustness limits remain implementation work, not format claims.

Compatibility fixture

tests/vectors/locator-v11.json is the byte interoperability fixture for payload 00 01 ... 0F. The current renderer and C ABI must produce and decode it exactly.