Flight Path

1export type LngLat = [number, number];
2
3// Chaikin corner cutting turns a sparse route into a continuous curve. Repeated passes round
4// direction changes into deliberate swerves instead of left-right heading bumps.
5export const smoothFlightPath = (source: LngLat[], passes = 3): LngLat[] => {
6	if (source.length < 2)
7		throw new Error('Flyover path needs at least two points');
8
9	// Keep adjacent longitudes continuous for routes that cross the antimeridian.
10	const unwrapped: LngLat[] = [source[0]];
11	for (let index = 1; index < source.length; index++) {
12		const [lng, lat] = source[index];
13		const previous = unwrapped[index - 1][0];
14		let adjusted = lng;
15		while (adjusted - previous > 180) adjusted -= 360;
16		while (adjusted - previous < -180) adjusted += 360;
17		unwrapped.push([adjusted, lat]);
18	}
19
20	let curve = unwrapped;
21	for (let pass = 0; pass < Math.max(0, passes); pass++) {
22		const next: LngLat[] = [curve[0]];
23		for (let i = 0; i < curve.length - 1; i++) {
24			const a = curve[i];
25			const b = curve[i + 1];
26			next.push(
27				[a[0] * 0.75 + b[0] * 0.25, a[1] * 0.75 + b[1] * 0.25],
28				[a[0] * 0.25 + b[0] * 0.75, a[1] * 0.25 + b[1] * 0.75],
29			);
30		}
31		next.push(curve[curve.length - 1]);
32		curve = next;
33	}
34	return curve;
35};