The Google maps API does not already provide a method for checking points in polygons. After researching a bit I stumbled across the Ray-casting algorithm which will determine if an X-Y coordinate is inside a plotted shape. This will translate to latitude and longitude. The following extends the google.maps.polygon.prototype to use this algorithm. Simply include this code at a point in the code after google.maps has loaded:
google.maps.Polygon.prototype.Contains = function(point) { var crossings = 0, path = this.getPath();
// for each edge for (var i=0; i < path.getLength(); i++) { var a = path.getAt(i), j = i + 1; if (j >= path.getLength()) { j = 0; } var b = path.getAt(j); if (rayCrossesSegment(point, a, b)) { crossings++; } } // odd number of crossings? return (crossings % 2 == 1); function rayCrossesSegment(point, a, b) { var px = point.lng(), py = point.lat(), ax = a.lng(), ay = a.lat(), bx = b.lng(), by = b.lat(); if (ay > by) { ax = b.lng(); ay = b.lat(); bx = a.lng(); by = a.lat(); } // alter longitude to cater for 180 degree crossings if (px < 0) { px += 360 }; if (ax < 0) { ax += 360 }; if (bx < 0) { bx += 360 }; if (py == ay || py == by) py += 0.00000001; if ((py > by || py < ay) || (px > Math.max(ax, bx))) return false; if (px < Math.min(ax, bx)) return true; var red = (ax != bx) ? ((by - ay) / (bx - ax)) : Infinity; var blue = (ax != px) ? ((py - ay) / (px - ax)) : Infinity; return (blue >= red); } };
Here we have extended the functionality of google.maps.Polygon by defining a function with name ‘Contains’ which can be used to determine whether the latitude longitude provided in function parameter are within the polygon or not. Here we make use of Ray-casting algorithm and developed a function using the same. After doing this much of exercise now, we can check a point as follows:
var point = new google.maps.LatLng(52.05249047600099, -0.6097412109375); var polygon = new google.maps.Polygon({path:[INSERT_PATH_ARRAY_HERE]}); if (polygon.Contains(point)) { // point is inside polygon }
For complete code and demo please go to: http://counsellingbyabhi.blogspot.in/2013/01/google-map-check-whether-point-latlong.html