Set and Drift API

Current-sailing (set and drift) navigation maths as an API, computed locally and deterministically — the course-over-ground, course-to-steer and current numbers a mariner, navigator or marine app plots a passage with. The course-made-good endpoint adds the boat's velocity through the water to the current vector to give the real track: the course over ground (COG) and speed over ground (SOG), with the drift angle the current pushes you off your nose — steering 090° through the water at 10 knots with a 2-knot current setting north comes out around 079° over the ground at 10.2 knots. The course-to-steer endpoint solves the other way: the heading to steer to make good a desired ground track, steering up-current to cancel the across-track set (sin(H−T) = −drift·sin(set−track) ÷ speed), and the resulting SOG — usually slower into a current, faster with it astern, and impossible if the current across the track beats your speed. The current endpoint finds the set and drift from the offset between a dead-reckoning position and an observed fix: the set is the bearing DR-to-fix and the drift is that distance ÷ the elapsed time, ready to carry forward. Everything is computed locally and deterministically, so it is instant and private. Ideal for marine-navigation and chartplotter apps, sailing and boating tools, and maritime-training utilities. Pure local computation — no key, no third-party service, instant. Degrees true. 3 compute endpoints. For great-circle distance use a geo-distance API; for tide times a tides API.