gis-utils/dist/index.js

Some GIS utility functions I have used in multiple projects.

'use strict';

/**
 * Helper function - converts degrees to radians
 *
 * @param {number}  degrees
 *
 * @return {number}
 */
function deg2rad(degrees) {
  return degrees * Math.PI / 180;
}

/**
 * Helper function - inverse of above
 * 
 * @param  {number} angle 
 * 
 * @return {number}
 */
function rad2deg(angle) {
  return angle * 57.29577951308232; // angle / Math.PI * 180
}

/**
 * Returns the distance in km on a sphere between fromLocation and toLocation
 * Expects Objects like: { lat: 1.100, lng: 59.00 }
 *  
 * @param  {Object} fromLocation
 * @param  {Object} toLocation
 * 
 * @return {number}
 */
function haversineKm(fromLocation, toLocation) {

  var radius_of_earth_kms = 6371;

  var dLat = deg2rad(fromLocation.lat - toLocation.lat);
  var dLng = deg2rad(fromLocation.lng - toLocation.lng);

  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.sin(dLng / 2) * Math.sin(dLng / 2) * Math.cos(deg2rad(fromLocation.lat)) * Math.cos(deg2rad(toLocation.lat));

  var c = 2 * Math.asin(Math.sqrt(a));

  return radius_of_earth_kms * c;
}

/**
 * Finds the radius of the circle which would fully enclose the current map
 *
 * @param  {google.maps.LatLngBounds} bounds   The google maps bounds object
 * 
 * @return {number}
 */
function calculateRadiusFromMapBounds(bounds) {

  // get the corners
  var pointNE = bounds.getNorthEast();
  var pointNELatLng = {
    lat: pointNE.lat(),
    lng: pointNE.lng()
  };
  var pointSW = bounds.getSouthWest();
  var pointSWLatLng = {
    lat: pointSW.lat(),
    lng: pointSW.lng()
  };

  // calculate the diagonal
  var diagonalDistanceKm = haversineKm(pointNELatLng, pointSWLatLng);

  // radius is half the diagonal
  return diagonalDistanceKm / 2;
}

/**
 * Returns a an object for the bounds NE/SW bounds which fits inside a circle
 * at point center with radius radius (in m)
 * 
 * @param  {number} radius The radius in m
 * @param  {Object} center object representing the center
 * 
 * @return {Object}
 */
function getNESWBoundsFromRadiusAndCenter(radius, center) {

  var earthRadiusM = 6378137;

  var pointNE = computeDestinationPoint(center.lat, center.lng, radius, 45, earthRadiusM);

  var pointSW = computeDestinationPoint(center.lat, center.lng, radius, 225, earthRadiusM);

  return {
    'ne': pointNE,
    'sw': pointSW
  };
}

/**
 * As above, but for NW and SE
 * 
 * @param  {number} radius The radius in m
 * @param  {Object} center object representing the center
 * 
 * @return {Object}
 */
function getNWSEBoundsFromRadiusAndCenter(radius, center) {

  var earthRadiusM = 6378137;

  var pointNW = computeDestinationPoint(center.lat, center.lng, radius, 315, earthRadiusM);

  var pointSE = computeDestinationPoint(center.lat, center.lng, radius, 135, earthRadiusM);

  return {
    'nw': pointNW,
    'se': pointSE
  };
}

/**
 * Computes the destination point given an initial point, a distance
 * and a bearing
 *
 * See http://www.movable-type.co.uk/scripts/latlong.html for the original code
 *
 * @param  {number} lat         latitude of the initial point in degree
 * @param  {number} lon         longitude of the initial point in degree
 * @param  {number} distance    distance to go from the initial point in meter
 * @param  {number} bearing     bearing in degree of the direction to go, e.g.
 *                                0 = north, 180 = south
 * @param  {number} radius      mean radius of the earth (in meters)
 * 
 * @return       object         { latitude: destLat  longitude: destLng }
 */
function computeDestinationPoint(lat, lon, distance, bearing, radius) {

  var delta = Number(distance) / radius; // angular distance in radians
  var theta = deg2rad(Number(bearing));

  var phi1 = deg2rad(Number(lat));
  var lambda1 = deg2rad(Number(lon));

  var phi2 = Math.asin(Math.sin(phi1) * Math.cos(delta) + Math.cos(phi1) * Math.sin(delta) * Math.cos(theta));

  var lambda2 = lambda1 + Math.atan2(Math.sin(theta) * Math.sin(delta) * Math.cos(phi1), Math.cos(delta) - Math.sin(phi1) * Math.sin(phi2));

  // normalise to -180..+180°
  lambda2 = (lambda2 + 3 * Math.PI) % (2 * Math.PI) - Math.PI;

  return { lat: rad2deg(phi2), lng: rad2deg(lambda2) };
}

/**
 * Determines if a point is within a NE/SW boundary
 
 * @param  {Object}  point    
 * @param  {Object}  boundary 
 * 
 * @return {Boolean}
 */
function isLatAndLngInRectBoundary(point, boundary) {

  // handling for the rare occasion where we might go from 359deg to 0deg on 
  // international date line
  var eastBound = point.lng < boundary.NE.lng;
  var westBound = point.lng > boundary.SW.lng;

  var inLng;

  if (boundary.NE.lng < boundary.SW.lng) {
    inLng = eastBound || westBound;
  } else {
    inLng = eastBound && westBound;
  }

  var inLat = point.lat > boundary.SW.lat && point.lat < boundary.NE.lat;

  return inLat && inLng;
}

module.exports = {
  deg2rad: deg2rad,
  rad2deg: rad2deg,
  haversineKm: haversineKm,
  calculateRadiusFromMapBounds: calculateRadiusFromMapBounds,
  getNESWBoundsFromRadiusAndCenter: getNESWBoundsFromRadiusAndCenter,
  getNWSEBoundsFromRadiusAndCenter: getNWSEBoundsFromRadiusAndCenter,
  computeDestinationPoint: computeDestinationPoint,
  isLatAndLngInRectBoundary: isLatAndLngInRectBoundary
};