Creates a point on the earth's surface at the supplied latitude / longitude - Node.js Geometry

Node.js examples for Geometry:Latitude Longitude

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Description

Creates a point on the earth's surface at the supplied latitude / longitude

Demo Code

/**//from   w w  w  . j  a  va  2  s . c  o m
 * Creates a point on the earth's surface at the supplied latitude / longitude
 *
 * @constructor
 * @param {Number} lat: latitude in numeric degrees
 * @param {Number} lon: longitude in numeric degrees
 * @param {Number} [rad=6371004]: radius of earth if different value is required from standard 6,371,004m
 */
function LatLon(lat, lon, rad) {
  if (typeof(rad) == 'undefined') rad = 6371004;  // earth's mean radius in m
  // only accept numbers or valid numeric strings
  this._lat = typeof(lat)=='number' ? lat : typeof(lat)=='string' && lat.trim()!='' ? +lat : NaN;
  this._lon = typeof(lon)=='number' ? lon : typeof(lon)=='string' && lon.trim()!='' ? +lon : NaN;
  this._radius = typeof(rad)=='number' ? rad : typeof(rad)=='string' && trim(lon)!='' ? +rad : NaN;
}

/**
 * Returns the distance from this point to the supplied point, in m 
 * (using Haversine formula)
 *
 * from: Haversine formula - R. W. Sinnott, "Virtues of the Haversine",
 *       Sky and Telescope, vol 68, no 2, 1984
 *
 * @param   {LatLon} point: Latitude/longitude of destination point
 * @returns {Number} Distance in m between this point and destination point
 */
LatLon.prototype.distanceTo = function(point) {

  var R = this._radius;
  var lat1 = this._lat.toRad(), lon1 = this._lon.toRad();
  var lat2 = point._lat.toRad(), lon2 = point._lon.toRad();
  var dLat = lat2 - lat1;
  var dLon = lon2 - lon1;

  var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
          Math.cos(lat1) * Math.cos(lat2) * 
          Math.sin(dLon/2) * Math.sin(dLon/2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  var d = R * c;
  return d;
}

/**
 * Returns the midpoint between this point and the supplied point.
 * 
 *
 * @param   {LatLon} point: Latitude/longitude of destination point
 * @returns {LatLon} Midpoint between this point and the supplied point
 */
LatLon.prototype.midpointTo = function(point) {
  lat1 = this._lat.toRad(), lon1 = this._lon.toRad();
  lat2 = point._lat.toRad();
  var dLon = (point._lon-this._lon).toRad();

  var Bx = Math.cos(lat2) * Math.cos(dLon);
  var By = Math.cos(lat2) * Math.sin(dLon);

  lat3 = Math.atan2(Math.sin(lat1)+Math.sin(lat2),
                    Math.sqrt( (Math.cos(lat1)+Bx)*(Math.cos(lat1)+Bx) + By*By) );
  lon3 = lon1 + Math.atan2(By, Math.cos(lat1) + Bx);
  lon3 = (lon3+3*Math.PI) % (2*Math.PI) - Math.PI;  // normalise to -180..+180o
  
  return new LatLon(lat3.toDeg(), lon3.toDeg());
}

/** Converts numeric degrees to radians */
if (typeof Number.prototype.toRad == 'undefined') {
  Number.prototype.toRad = function() {
    return this * Math.PI / 180;
  }
}

/** Converts radians to numeric (signed) degrees */
if (typeof Number.prototype.toDeg == 'undefined') {
  Number.prototype.toDeg = function() {
    return this * 180 / Math.PI;
  }
}

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