Definition
Computed from the relative velocity vector between own ship and the target using their reported positions, courses and speeds over ground. Displays present CPA in nautical miles alongside time to CPA in minutes, with user-set alarm thresholds, for instance 1.0 nautical mile and 12 minutes offshore. Because AIS CPA uses ground-referenced data it can differ from radar-derived CPA in a strong tidal stream, and it assumes both vessels maintain their present motion.
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