CKey locator format v0.13.0 (draft)

Status: experimental. New locator frames use format=13 (0D) and profile=1; older locator formats remain decoder-readable for compatibility.

External-corner finder geometry

The canonical field is 29 by 29 units. Its finder geometry forms the actual convex outside corners of the symbol, not marks inset inside a rounded rectangle. The four straight frame sides run at coordinate 0.5 / 28.5 and stop at the corner tangent points. Each finder is three round-capped quarter arcs with common centre at the physical corner: (0.5,0.5) for top-left and its reflections for the other corners. Centerline radii are 1.80, 2.65, and 3.50 units; all strokes are 0.65 units. The 3.50-unit arc joins the structural side segments and is therefore the rounded outer corner itself.

Top-right, bottom-right, and bottom-left arc sets are continuous. Every top-left arc has a cap-compensated 0.95-unit visible gap centered on the 45-degree diagonal. That split is the orientation signature. The corner envelopes remain reserved from payload.

Remaining locator rules

All other Format 0.8/0.12 locator rules remain: 16-byte payload; frame C7 4B 0D 01 00 10, CRC-32C, systematic shortened RS(77,26) over GF(256) with polynomial 0x11D, 51 parity bytes, and up to 25 unknown byte-error correction. Grid Key, Ray Key, Ring Key, Cartesian/polar placement, rings, ray band, and logo-safe centre are unchanged. The reader uses keys and finder geometry for optical fit but only accepts a result after RS and CRC validation.

The normative vector is locator-v13.json.