Radar Observer · Plotting — CPA
On a relative-motion plot, the closest point of approach (CPA) is found by:
- AReading the target's first plotted position
- BDropping a perpendicular from own ship (display center) to the relative-motion line✓ Correct
- CMeasuring the target's true course
- DTaking the average of all ranges
Explanation
Extending the relative-motion line and dropping a perpendicular from the center (own ship) gives the CPA distance; where the target reaches that point in time gives the TCPA. A small CPA indicates risk of collision.
Authority: Radar Navigation — CPA
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