Get bbox from coordinates and distance

getBoundingBox-center-distance.js

/**
 * Get bounding box from set of coordinates [lat,lng] and distance in (deg) adopted to JS
 * 
 * @param {number} distance - distance (deg) from the point represented by centerPoint
 * @param {array} centerPoint - two-dimensional array containing center coords [latitude, longitude]
 * @description
 *   Computes the bounding coordinates of all points on the surface of a sphere
 *   that has a great circle distance to the point represented by the centerPoint
 *   argument that is less or equal to the distance argument.
 *   Technique from: Jan Matuschek <http://JanMatuschek.de/LatitudeLongitudeBoundingCoordinates>
 * @author Alex Salisbury
*/
export const getBoundingBox = function getBoundingBox(centerPoint, distance) {
  if (distance < 0) {
    return 'Illegal arguments';
  }

  // coordinate limits
  const MIN_LAT = degToRad(-90);
  const MAX_LAT = degToRad(90);
  const MIN_LON = degToRad(-180);
  const MAX_LON = degToRad(180);
  // Earth's radius (km)
  const R = 6378.1;
  // angular distance in radians on a great circle

  // (degrees * PI * diameter / 360) * cos (latitude)
  const radDist = (distance * 111) / R;
  // center point coordinates (deg)
  const degLat = centerPoint[0];
  const degLon = centerPoint[1];

  // center point coordinates (rad)
  const radLat = degToRad(degLat);
  const radLon = degToRad(degLon);
  // minimum and maximum latitudes for given distance
  let minLat = radLat - radDist;
  let maxLat = radLat + radDist;
  // minimum and maximum longitudes for given distance
  let minLon;
  let maxLon;
  // define deltaLon to help determine min and max longitudes
  const deltaLon = Math.asin(Math.sin(radDist) / Math.cos(radLat));
  if (minLat > MIN_LAT && maxLat < MAX_LAT) {
    minLon = radLon - deltaLon;
    maxLon = radLon + deltaLon;
    if (minLon < MIN_LON) {
      minLon = minLon + 2 * Math.PI;
    }
    if (maxLon > MAX_LON) {
      maxLon = maxLon - 2 * Math.PI;
    }
  // a pole is within the given distance
  } else {
    minLat = Math.max(minLat, MIN_LAT);
    maxLat = Math.min(maxLat, MAX_LAT);
    minLon = MIN_LON;
    maxLon = MAX_LON;
  }

  return latLngBounds(
    // SW
    latLng(radToDeg(minLat), radToDeg(minLon)),
    // NE
    latLng(radToDeg(maxLat), radToDeg(maxLon))
  );
};