Android GoogleMaps，如何检查多边形内的点（经度和纬度）

Question

there has been some questions about latitude and longitude inside a polygon

but i still don't get any answer for my problem

here is my problem :

let's say we have a polygon looks like a rectangle

(in real problem , it won't shape only like a rectangle, it could have more than 2 points, maybe 100 points maximal)

where

-the top left point is combination of latitude = 100.214525 and longitude = 102.12866735
-the top right point is combination of latitude = 105.21335 and longitude = 101.12882515
-the bottom left point is combination of latitude = 29.214124 and longitude = 20.16873
-the bottom right point is combination of latitude = 30.216125 and longitude = 18.1286860

(all latitude and longitude there is only an example)

Now that i have 4 point , there should be a polygon with 4 point , and try to draw a line from one point to another (there won't be any hole inside the polygon)

now let's say , i have 2 user

Let's say

Latitude 78.25151 and Longitude 67.2121021 is the User A's coordinate

and

Latitude 28.25151 and Longitude 157.2121021 is the User B's coordinate

I need some algorithm or something that could determine if User A / B's coordinate inside the polygon

(something that will return true if user's coordinate is inside the polygon , or else will return false without displaying anything to the user)

FYI

i have researched it using javascript

here is my javascript

if (!google.maps.Polygon.prototype.getBounds) {
            google.maps.Polygon.prototype.getBounds = function(latLng) {
                var bounds = new google.maps.LatLngBounds();
                var paths = this.getPaths();
                var path;

                for (var p = 0; p < paths.getLength(); p++) {
                    path = paths.getAt(p);
                    for (var i = 0; i < path.getLength(); i++) {
                        bounds.extend(path.getAt(i));
                    }
                }

                return bounds;
            }
        }   



        google.maps.Polygon.prototype.containsLatLng = function(latLng) {

            var lat, lng;

            if(arguments.length == 2) {
                if(typeof arguments[0]=="number" && typeof arguments[1]=="number") {
                    lat = arguments[0];
                    lng = arguments[1];
                }
            } 
            else if (arguments.length == 1) {
                var bounds = this.getBounds();

                if(bounds != null && !bounds.contains(latLng)) {
                    return false;
                }
                lat = latLng.lat();
                lng = latLng.lng();
            } 
            else {
                console.log("Wrong number of inputs in google.maps.Polygon.prototype.contains.LatLng");
            }

            // Raycast point in polygon method
            var inPoly = false;

            var numPaths = this.getPaths().getLength();
            for(var p = 0; p < numPaths; p++) {
                var path = this.getPaths().getAt(p);
                var numPoints = path.getLength();
                var j = numPoints-1;

                for(var i=0; i < numPoints; i++) { 
                    var vertex1 = path.getAt(i);
                    var vertex2 = path.getAt(j);

                    if (vertex1.lng() < lng && vertex2.lng() >= lng || vertex2.lng() < lng && vertex1.lng() >= lng) {
                        if (vertex1.lat() + (lng - vertex1.lng()) / (vertex2.lng() - vertex1.lng()) * (vertex2.lat() - vertex1.lat()) < lat) {
                            inPoly = !inPoly;
                        }
                    }

                    j = i;
                }
            }

            return inPoly;
        }

as you can see

that code contains 2 functions (containsLatLng and getBounds) and with those functions, i could easily get the boolean if my latitude and longitude is inside a polygon

like this example :

var triangleCoords = [
  new google.maps.LatLng(25.774252, -80.190262),
  new google.maps.LatLng(18.466465, -66.118292),
  new google.maps.LatLng(32.321384, -64.75737) 
];

var bermudaTriangle = new google.maps.Polygon({
paths: triangleCoords,
strokeColor: '#FF0000',
strokeOpacity: 0.8,
strokeWeight: 3,
fillColor: '#FF0000',
fillOpacity: 0.35
});
var myLatitudeLongitude = new google.maps.LatLng(24.886436490787712, -70.2685546875);

alert(bermudaTriangle.containsLatLng(myLatitudeLongitude));

but that is javascript

now in android, i don't know if there is such a thing like google.maps.Polygon or google.maps.LatLngBounds as you can see these two are required for my javascript function

or is there any other ways to do something like this without depends on these two javascript functions?

Answer 1

The problem you raised is commonly called Point in Polygon algorithm.
You should explain us where you'd like to implement it. In the view, server-side, or in your DB ?

However, here is the explaination of the algorithm's idea, and its implementation in C (I never implement it for Android, sorry).

You could also google "point in polygon [language in which you'd like to implement it], there are a lot of resources ont he Internet