Does this polyline pass through this polygon? - google-maps

Question

I’m trying to test whether a Google Maps polyline passes through a Google Maps polygon. Sounds simple. But I’ve searched and searched... and found no real answers.
Closest I got was this function. It works but, frustratingly, returns the occasional false positive.
//nvert = the number of points in the polygon
//vertx = an array of all the polygon's latitudes
//verty = an array of all the polygon's longitudes
//elat = the current point's latitude
//elng = the current point's longitude
function pnpoly( nvert, vertx, verty, elat, elng) {
var i, j, c = false;
for( i = 0, j = nvert-1; i < nvert; j = i++ ) {
if( ( ( verty[i] > elng ) != ( verty[j] > elng ) ) &&
( elat < ( vertx[j] - vertx[i] ) * ( elng - verty[i] ) / ( verty[j] - verty[i] ) + vertx[i] ) ) {
c = !c;
}
}
return c;
}
Before I try a whole new method (a crazy math idea that brings me back to Grade 12 calculus), I’m wondering anyone knows how to accomplish this.

Answer 1

I've come across a working solution.
https://github.com/albertsun/JavaScript-Geometry
This geometry package includes a function called findIntersections().
I ran an $.each loop on each polygon on my map, then pushed each point in the polygon into an array, then each point in the polyline into an array. Finally, I ran two loops and pushed the lat/lon coordinates into variables for the function. It returns empty when it doesn't find anything and returns the coordinates of intersection when it finds something.
function processPath(polyline, polygons){
$.each(polygons, function(i,polygon){
var polygonArr = [] // array for storing each point in polygon
polygon.getPaths().forEach(function(k,g){
$.each(k.b, function(l,m){
polygonArr.push({'lat':m.lat(),'lng':m.lng()});
});
});
//Get the number of points in the polyLINE
var numStops = polyline.getPath().b.length -1;
//Get the path and coordinates of the polyLINE
var polylineArr = [];
polyline.getPath().forEach(function(z,y){
polylineArr.push({'lat':z.lat(),'lng':z.lng()});
});
$.each(polygonArr, function(j, polygon){
$.each(polylineArr, function(k, polyline){
if(k+1 != polylineArr.length){
var lineCoor1x = polylineArr[k].lat;
var lineCoor1y = polylineArr[k].lng;
var lineCoor2x = polylineArr[k+1].lat;
var lineCoor2y = polylineArr[k+1].lng;
var polyCoorx = polygonArr[j].lat;
var polyCoory = polygonArr[j].lng;
if(j+1 == polygonArr.length){
// We've reached the end, go back to the start
var polyCoorNextx = polygonArr[0].lat
var polyCoorNexty = polygonArr[0].lng
} else {
// Go to the next point
var polyCoorNextx = polygonArr[j+1].lat
var polyCoorNexty = polygonArr[j+1].lng
}
if(findIntersections([[[lineCoor1x,lineCoor1y], [lineCoor2x,lineCoor2y]], [[polyCoorx,polyCoory],[polyCoorNextx,polyCoorNexty]] ]).length != 0){
whereInside[i] = i;
return;
}
}
})
})
It's probably a bit messy but it works.