Qibla.ts

import Coordinates from './Coordinates';
import { degreesToRadians, radiansToDegrees, unwindAngle } from './MathUtils';

export default function qibla(coordinates: Coordinates) {
  const makkah = new Coordinates(21.4225241, 39.8261818);

  // Equation from "Spherical Trigonometry For the use of colleges and schools" page 50
  const term1 = Math.sin(
    degreesToRadians(makkah.longitude) -
      degreesToRadians(coordinates.longitude),
  );
  const term2 =
    Math.cos(degreesToRadians(coordinates.latitude)) *
    Math.tan(degreesToRadians(makkah.latitude));
  const term3 =
    Math.sin(degreesToRadians(coordinates.latitude)) *
    Math.cos(
      degreesToRadians(makkah.longitude) -
        degreesToRadians(coordinates.longitude),
    );
  const angle = Math.atan2(term1, term2 - term3);

  return unwindAngle(radiansToDegrees(angle));
}