Checking User is inside Polygone on Googlemap or not.. - Flutter [duplicate] - flutter

Question

I'm working on flutter project using google-maps-flutter plugin, and I want to check if the user location is inside the polygon that I created on the map. There is an easy way using JavaScript api (containsLocation() method) but for flutter I only found a third party plugin,google_map_polyutil, which is only for android and I get a security worming when I run my app. Is there another way to do so??

Answer 1

I found this answer and just modified some minor things to work with dart, I ran a test on a hardcoded polygon. The list _area is my polygon and _polygons is required for my mapcontroller.
final Set<Polygon> _polygons = {};
List<LatLng> _area = [
LatLng(-17.770992200, -63.207739700),
LatLng(-17.776386600, -63.213576200),
LatLng(-17.778348200, -63.213576200),
LatLng(-17.786848100, -63.214262900),
LatLng(-17.798289700, -63.211001300),
LatLng(-17.810547700, -63.200701600),
LatLng(-17.815450600, -63.185252100),
LatLng(-17.816267800, -63.170660900),
LatLng(-17.800741300, -63.153838100),
LatLng(-17.785867400, -63.150919800),
LatLng(-17.770501800, -63.152636400),
LatLng(-17.759712400, -63.160361200),
LatLng(-17.755952300, -63.169802600),
LatLng(-17.752519100, -63.186625400),
LatLng(-17.758404500, -63.195551800),
LatLng(-17.770992200, -63.206538100),
LatLng(-17.770996000, -63.207762500)];
The function ended like this:
bool _checkIfValidMarker(LatLng tap, List<LatLng> vertices) {
int intersectCount = 0;
for (int j = 0; j < vertices.length - 1; j++) {
if (rayCastIntersect(tap, vertices[j], vertices[j + 1])) {
intersectCount++;
}
}
return ((intersectCount % 2) == 1); // odd = inside, even = outside;
}
bool rayCastIntersect(LatLng tap, LatLng vertA, LatLng vertB) {
double aY = vertA.latitude;
double bY = vertB.latitude;
double aX = vertA.longitude;
double bX = vertB.longitude;
double pY = tap.latitude;
double pX = tap.longitude;
if ((aY > pY && bY > pY) || (aY < pY && bY < pY) || (aX < pX && bX < pX)) {
return false; // a and b can't both be above or below pt.y, and a or
// b must be east of pt.x
}
double m = (aY - bY) / (aX - bX); // Rise over run
double bee = (-aX) * m + aY; // y = mx + b
double x = (pY - bee) / m; // algebra is neat!
return x > pX;
}
Notice the polygons property and the onTap method. I was trying to check if the marker created in my map was inside my polygon:
GoogleMap(
initialCameraPosition: CameraPosition(
target: target, //LatLng(0, 0),
zoom: 16,
),
zoomGesturesEnabled: true,
markers: markers,
polygons: _polygons,
onMapCreated: (controller) =>
_mapController = controller,
onTap: (latLng) {
_getAddress(latLng);
},
)
Then i just used the following call in my _getAddress method:
_checkIfValidMarker(latLng, _area);
I hope it helps you to create what you need.

Answer 2

The easiest way to use it - https://pub.dev/packages/maps_toolkit
with isLocationOnPath method.

Answer 3

L. Chi's answer really help.
But due to I have pretty close points, rayCastIntersect might have wrong boolean return if aX is equal to bX
Therefore, I just add aX == bX condition check before calculate m then it works.
bool rayCastIntersect(LatLng tap, LatLng vertA, LatLng vertB) {
double aY = vertA.latitude;
double bY = vertB.latitude;
double aX = vertA.longitude;
double bX = vertB.longitude;
double pY = tap.latitude;
double pX = tap.longitude;
if ((aY > pY && bY > pY) || (aY < pY && bY < pY) || (aX < pX && bX < pX)) {
return false; // a and b can't both be above or below pt.y, and a or
// b must be east of pt.x
}
if (aX == bX) {
return true;
}
double m = (aY - bY) / (aX - bX); // Rise over run
double bee = (-aX) * m + aY; // y = mx + b
double x = (pY - bee) / m; // algebra is neat!
return x > pX;
}

Answer 4

The easiest way to use it - https://pub.dev/packages/maps_toolkit
with PolygonUtil.containsLocation - computes whether the given point lies inside the specified polygon.