Google Maps v3: check if point exists in polygon - google-maps

Question

I am looking to find a way of checking if a point exists inside a polygon in Google Maps v3 (JavaScript). I've searched everywhere and the only solutions I have found so far have been to do with getting the bounds of the polygon, but the code shown seems to just create a rectangle and keeps expanding its surface area to include all relevant points.
By the way, the reason I can't just use a big square i.e. getting a polygons bounds, is that I have bordering polygons on the map and they can not expand into each other's territory.
EDIT
Following on from the reply below, I have tried implementing the example code using one of my existing polygons but it is just saying that it is not defined and I can't figure out why.
Here is my declaration:
myCoordinates = [
new google.maps.LatLng(0.457301,-0.597382),
new google.maps.LatLng(0.475153,-0.569916),
new google.maps.LatLng(0.494379,-0.563049),
new google.maps.LatLng(0.506738,-0.553436),
new google.maps.LatLng(0.520470,-0.541077),
new google.maps.LatLng(0.531456,-0.536957),
new google.maps.LatLng(0.556174,-0.552063),
new google.maps.LatLng(0.536949,-0.596008),
new google.maps.LatLng(0.503991,-0.612488),
new google.maps.LatLng(0.473780,-0.612488) ];
polyOptions = {
path: myCoordinates,
strokeColor: "#FF0000",
strokeOpacity: 0.8,
strokeWeight: 2,
fillColor: "#0000FF",
fillOpacity: 0.6 };
var rightShoulderFront = new google.maps.Polygon(polyOptions);
rightShoulderFront.setMap(map);
and here is where I am checking for the point:
var coordinate = selectedmarker.getPosition();
var isWithinPolygon = rightShoulderFront.containsLatLng(coordinate);
console.log(isWithinPolygon);
But it keeps coming up with the error: Uncaught ReferenceError: rightShoulderFront is not defined

Answer 1

One algorithm to solve this is ray-casting. See an explanation here.
And you can find code implementing this for the Google Maps JS API V3 here.
HTH.

Answer 2

You can do this quite simply with Google maps geometry library.
First be sure to add the google maps geometry library.
<script type="text/javascript" src="//maps.googleapis.com/maps/api/js?libraries=geometry&sensor=false"></script>
Then, define your polygon
var rightShoulderFront = new google.maps.Polygon({
paths: myCoordinates
});
rightShoulderFront .setMap(map);
I'm going to add an event listener to handle a 'click' event, but you can adapt to fit your needs
google.maps.event.addListener(rightShoulderFront , 'click', isWithinPoly);
Create a function to handle our click event an check if coordinate exists within polygon using Google's geometry library
/** #this {google.maps.Polygon} */
function isWithinPoly(event){
var isWithinPolygon = google.maps.geometry.poly.containsLocation(event.latLng, this);
console.log(isWithinPolygon);
}

Answer 3

You have a very good example of containsLocation() method in Google Maps API documentation.

Answer 4

You should have a look about the Gmaps.js library. It has a quite simple method about geofence.

Answer 5

var coordinate = new google.maps.LatLng(0.457301,-0.597382);//replace with your lat and lng values
var isWithinPolygon = google.maps.geometry.poly.containsLocation(coordinate, yourPolygon);
Dont forget to include the library in your googleapis script. Read more...
<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&libraries=geometry"></script>

Answer 6

The example and implementation do not take into account that a polygon can cross the 180 degrees boundary.
The implementation does take it into account (implicitly) in the bounding box check, but the polygon check fails.

Answer 7

I have used the same thing and working fine and its offline code I have written this code in PHP you can write it any programming language.
class pointLocation {
var $pointOnVertex = true; // Check if the point sits exactly on one of the vertices?
function pointLocation() {
}
function pointInPolygon($point, $polygon, $pointOnVertex = true) {
$this->pointOnVertex = $pointOnVertex;
// Transform string coordinates into arrays with x and y values
$point = $this->pointStringToCoordinates($point);
$vertices = array();
foreach ($polygon as $vertex) {
$vertices[] = $this->pointStringToCoordinates($vertex);
}
// Check if the point sits exactly on a vertex
if ($this->pointOnVertex == true and $this->pointOnVertex($point, $vertices) == true) {
return "vertex";
}
// Check if the point is inside the polygon or on the boundary
$intersections = 0;
$vertices_count = count($vertices);
for ($i=1; $i < $vertices_count; $i++) {
$vertex1 = $vertices[$i-1];
$vertex2 = $vertices[$i];
if ($vertex1['y'] == $vertex2['y'] and $vertex1['y'] == $point['y'] and $point['x'] > min($vertex1['x'], $vertex2['x']) and $point['x'] < max($vertex1['x'], $vertex2['x'])) { // Check if point is on an horizontal polygon boundary
return "boundary";
}
if ($point['y'] > min($vertex1['y'], $vertex2['y']) and $point['y'] <= max($vertex1['y'], $vertex2['y']) and $point['x'] <= max($vertex1['x'], $vertex2['x']) and $vertex1['y'] != $vertex2['y']) {
$xinters = ($point['y'] - $vertex1['y']) * ($vertex2['x'] - $vertex1['x']) / ($vertex2['y'] - $vertex1['y']) + $vertex1['x'];
if ($xinters == $point['x']) { // Check if point is on the polygon boundary (other than horizontal)
return "boundary";
}
if ($vertex1['x'] == $vertex2['x'] || $point['x'] <= $xinters) {
$intersections++;
}
}
}
// If the number of edges we passed through is odd, then it's in the polygon.
if ($intersections % 2 != 0) {
return "inside";
} else {
return "outside";
}
}
function pointOnVertex($point, $vertices) {
foreach($vertices as $vertex) {
if ($point == $vertex) {
return true;
}
}
}
function pointStringToCoordinates($pointString) {
$coordinates = explode(" ", $pointString);
return array("x" => $coordinates[0], "y" => $coordinates[1]);
}
}
$pointLocation = new pointLocation();
$points = array("22.732965336387213 75.8609390258789");
$polygon = array("22.73549852921309 75.85424423217773","22.72346544538196 75.85561752319336","22.72346544538196 75.87175369262695","22.732332030848273 75.87295532226562","22.740406456758326 75.8686637878418","22.74198962160603 75.85407257080078");
echo '<pre>';
print_r($polygon);
// The last point's coordinates must be the same as the first one's, to "close the loop"
foreach($points as $key => $point) {
echo "point " . ($key+1) . " ($point): " . $pointLocation->pointInPolygon($point, $polygon) . "<br>";
}
?>

Answer 8

I think google has solved it with this method of containsLocation()
https://developers.google.com/maps/documentation/javascript/examples/poly-containsLocation