Parallel Navigation, Proportional Navigation and Range Vector Correlation from Interception by two predatory fly species is explained by a proportional navigation feedback controller

(a) Parallel navigation, depicted as two boats navigating at sea where boat A is attempting to intercept boat B. Parallel navigation describes the fact that as the two boats approach each other on a collision course, the line-of-sight does not rotate relative to the external world (here represented as North). This means that the bearing angle γ, formed between north and the LoS does not change over time. (b) Proportional navigation is represented as the response of Boat A to maintain a collision course. If the LoS rotates and thus changes the bearing of Boat B from A, then Boat A should magnify these rotations in its steering, multiplying them by a fixed navigational constant (N). (c) The process by which range vector correlation (an index of parallelism of successive LoS) is measured is diagrammatically represented in a step-by-step guide.