nearest.js

/**
  * Nearest:- finds the nearest things to a give thing, geospatially speaking 
  *
  * Eg, given an array of objects with a lat/lon properties
  *
  *     [
  *         { place: 'london',      lat: , lon: },
  *         { place: 'manchester',  lat: , lon: },
  *         { place: 'cardiff',     lat: , lon: },
  *     ]
  *
  */

var Nearest = function () {

    // credit: http://www.perlmonks.org/?node_id=150054
    this.distanceInKm = function (lat1,lon1,lat2,lon2) {
        var deg2rad = function(deg) { return deg * (Math.PI/180) }
          , R = 6371 // Radius of the earth in km
          , dLat = deg2rad(lat2-lat1)
          , dLon = deg2rad(lon2-lon1)
          , a = 
                Math.sin(dLat/2) * Math.sin(dLat/2) +
                Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) * 
                Math.sin(dLon/2) * Math.sin(dLon/2)
          , c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))
          , d = R * c; // Distance in km
          return d;
    }

    this.find = function( dataSource, opts ) {

        var opts = opts || {}
          , within = opts.within || 10 
          , limit = opts.limit || 50
          , lat = opts.coords[0]
          , lon = opts.coords[1]
          , that = this;

        return dataSource.map(function (record, index) { // calculate distance from give coords
            return {
             distance: parseFloat(that.distanceInKm(lat, lon, record.lat, record.lon).toFixed(2)),
             i: index 
           }
        }).sort(function (a,b) { // sort by distance
            return a.distance - b.distance
        }).filter(function (record) { // remove records above a given distance 
            return record.distance < within 
        }).map(function (record) { // return the original record
            dataSource[record.i].distance = record.distance;
            return dataSource[record.i];
        }).slice(0, limit)
    }

    return this;
}

module.exports = Nearest;