polygonIncludes.js

var polygonIncludes = function(points) {
  return function() {
    var point = [this.grid_lat, this.grid_lng];
    var sides = points.length;
    var map = function( elems, callback, arg ) {
      var ret = [], value;

      // Go through the array, translating each of the items to their
      // new value (or values).
      for ( var i = 0, length = elems.length; i < length; i++ ) {
        value = callback( elems[ i ], i, arg );

        if ( value != null ) {
          ret[ ret.length ] = value;
        }
      }

      return ret.concat.apply( [], ret );
    }

    var polyXs = map(points, function(p, i) { return p[0]; }),
        polyYs = map(points, function(p, i) { return p[1]; }),
        x = point[0],
        y = point[1];

    var max = function(arr) { return Math.max.apply({}, arr); },
        min = function(arr) { return Math.min.apply({}, arr); };

    if(max(polyXs) < x || min(polyXs) > x || max(polyYs) < y || min(polyYs) > y) {
      return false;
    }

    var result = false,
        j = sides - 1;

    for(var i = 0; i < sides; i++) {
      if((polyYs[i] < y && polyYs[j] >= y) || (polyYs[j] < y && polyYs[i] >= y)) {
        if((polyXs[i] + (y - polyYs[i])/(polyYs[j] - polyYs[i])*(polyXs[j] - polyXs[i])) < x) {
          result = !result;
        }
      }
      j = i;
    }

    return result;
  };
};