Typescript code for calculating distance between two gps coordinates.

geodistance.ts

/**
 * Enumeration of Earth's radius for a given distance unit
 * The value can be used as the radius value in a great circle calculation
 * @readonly
 * @enum {number}
 */
const enum EarthRadius {
  FEET = 2.0925e+7,
  KILOMETERS = 6378.0,
  METERS = 6378000.0,
  MILES = 3963.0,
}

/**
 * Coordinate Point type
 * @typedef {Object} CoordinatePoint
 * @property {number} latitude latitude of the coordinate
 * @property {number} longitude longitude of the coordinate
 */
type CoordinatePoint = {
  latitude: number,
  longitude: number,
};

/**
 * Convert a Coordinate Point in degrees to a Coordinate Point in radians
 * @param point {CoordinatePoint} the Coordinate Point with latitude and longitude expressed as degrees
 * @returns {CoordinatePoint} coordinate point with latitude and longitude expressed as radians
 */
const convertToRadians = (point: CoordinatePoint): CoordinatePoint => {
  // latitude and longitude are degree values
  // there are 360 degrees in a circle and 2 * Math.PI radians in a circle
  // 360 / (2 * Math.PI) = 57.29577951308232
  // 1 radian = 57.29577951308232 degrees
  // Divide degrees by this number to get the number of radians
  const DEGREE_DIVIDER = 57.29577951308232;

  return {
    latitude: point.latitude / DEGREE_DIVIDER,
    longitude: point.longitude / DEGREE_DIVIDER,
  };
};

/**
 * Measure the distance between two latitude/longitude coordinates. Uses great circle formula.
 * @param from {CoordinatePoint} the first coordinate point
 * @param to {CoordinatePoint} the second coordinate point
 * @param precision {number} the decimal precision to use for the returned value, default is 2
 * @param radius {EarthRadius} the radius by which to multiply the result, default is 3963.0 (returns miles)
 * @returns {number} the distance between the two supplied coordinate points
 */
const getDistance = (
  from: CoordinatePoint,
  to: CoordinatePoint,
  precision = 2,
  radius: EarthRadius = EarthRadius.MILES,
): number => {
  // convert coordinate point units from degrees to radians
  const point1: CoordinatePoint = convertToRadians(from);
  const point2: CoordinatePoint = convertToRadians(to);

  // measure the distance between the two points in radians
  const result: number = Math.acos(
    (Math.sin(point1.latitude) * Math.sin(point2.latitude))
    + (Math.cos(point1.latitude) * Math.cos(point2.latitude) * Math.cos(point1.longitude - point2.longitude)),
  );

  // convert the distance in radians to the target unit of measurement
  const distance = radius * result;

  // round the distance to the desired precision
  return parseFloat(distance.toFixed(precision));
};