FA-69105 / Tide and marine navigation tables / Member archive

Vertical datum conversion: Chart datum is unknown unless listed · case 05

Conversions to or from CD return None.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [kind, value, frm, to, table]: table lists [datum, offset above chart datum]; CD itself has offset 0 even if absent. Heights and drying heights are measured upward from their datum; depths downward. Converting frm->to: height=value+off[frm]-off[to], depth=value-off[frm]+off[to]. Unknown datum names return None. Result rounded to 3 decimals.

Why this case matters

Tide tables and passage plans turn published predictions into go/no-go decisions about depth, clearance and timing.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
vertical datum conversion ["drying", 1.4, "CD", "LAT", [["LAT", -0.3], ["MLWS", 0.5], ["MSL", 2.4], ["MHWS", 4.6]]]	`null`	`1.7`	Failed

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