Google Maps v3: check if point exists in polygon

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

score 50 · Accepted Answer · answered Jun 29 '11 at 14:43

50

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.

answered Jun 29 '11 at 14:43

mhyfritz

8,342
2
29
29

Do you have any running code? Maybe codepen or jsfiddle? Thanks. – Daniel Carpio Contreras Apr 09 '19 at 22:21

score 27 · Answer 2 · answered May 21 '13 at 16:53

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);
}

Is there any limitation put by Google on usage of this method, 'containsLocation()'? — A J, Oct 14 '15 at 12:38

Damjan Pavlica · Answer 3 · 2016-08-24T09:27:29.067

12

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

edited Aug 24 '16 at 09:27

answered Apr 14 '15 at 10:53

Damjan Pavlica

31,277
10
71
76

score 5 · Answer 4 · answered Apr 13 '14 at 08:18

5

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

answered Apr 13 '14 at 08:18

vtproduction

147
3
10

Gmaps.js is awesome ;) – cwhisperer May 01 '18 at 14:09

score 4 · Answer 5 · answered May 26 '17 at 05:27

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>

score 3 · Answer 6 · answered Dec 04 '17 at 11:10

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>";
}

?>

score 3 · Answer 7 · answered Jul 25 '11 at 13:51

3

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.

answered Jul 25 '11 at 13:51

rikkertkoppes

31
1

score 0 · Answer 8 · answered Aug 16 '22 at 06:02

0

I think google has solved it with this method of containsLocation()

https://developers.google.com/maps/documentation/javascript/examples/poly-containsLocation

answered Aug 16 '22 at 06:02

Ali Samie

145
2
11

Google Maps v3: check if point exists in polygon

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