Google Maps. Detect if one of the points on the polyline paths intersects a circle

readme.md

Working example

First, it checks if one of the points of the path is inside the circle. Then, checks every segment of the path and calculates the nearest point of the segment to the circle; if it's less than the circle radius, then, there is an intersection.

To Do

• Better performance by reducing the numbers of segments. Only the closests one depending on the points.
• Remove map as argument

Help From Circle line collision detection

maps.utils.js

(function(){
  var polyline = new google.maps.Polyline();
  
  google.maps.Polyline.prototype.closestDistanceToSegment = function(center, segment)
  {
    var firstPoint, lastPoint, A, B, C, D, E, distanceAB, t, projection = this.getMap().getProjection();
    
    // The other extreme of the path
    lastPoint  = segment[0];
    
    // One extreme of the path
    firstPoint = segment[1];
        
    //  C
    //  |\ 
    //  | \
    //  |  \
    //  |_ _\
    //  A    B
    //
    // Transform to points
    A = projection.fromLatLngToPoint(lastPoint);  
    B = projection.fromLatLngToPoint(firstPoint);
    C = projection.fromLatLngToPoint(center);
   
    // Calculte distance between A and B
    distanceAB = Math.sqrt( Math.pow(A.x-B.x, 2)+Math.pow(A.y -B.y, 2) );
   
    // Compute the direction vector D from A to B
    D = { x: (B.x-A.x)/distanceAB, y: (B.y-A.y)/distanceAB };
   
    t = D.x*(C.x-A.x) + D.y*(C.y-A.y);
   
    // LatLng of the point 
    E = projection.fromPointToLatLng({ x: t*D.x+A.x, y: t*D.y+A.y });
      
    polyline.setPath(segment);
    
    // En la docuemntacion poly.containsLocation sirve para Polygonos.
    // poly.isLocationOnEdge no es muy preciso
    if(google.maps.geometry.poly.containsLocation(E, polyline))
    {
      return google.maps.geometry.spherical.computeDistanceBetween(E, center);
    }
    
    return Number.POSITIVE_INFINITY;   
  }
  
  google.maps.Polyline.prototype.intersectsCircle = function(circle)
  {
    var poly = this,
        path = poly.getPath(), 
        totalPoints = path.getLength(), 
        center = circle.getCenter(), 
        radius = circle.getRadius(),
        intersect = false,
        indice = 0;
    
    while(indice < totalPoints && intersect === false){
      var point = path.getAt(indice++);
      if(google.maps.geometry.spherical.computeDistanceBetween(center, point) <= radius || 
        (indice < totalPoints && poly.closestDistanceToSegment(center, [point, path.getAt(indice)]) <= radius))
      {
        intersect = true;
      }
    }
    return intersect;
  }
})()

It's very good solution. Thanks for sharing.