该线不在两个位置之间出现（Google地图服务，Swift 4）

Question

我尝试在两个位置之间画线， 并且成功显示了origin的标记和destination的标记， 但是该行未出现在origin和destination ScreenShoot之间 我的代码：

import UIKit
import GoogleMaps
import GooglePlaces
import Alamofire
import SwiftyJSON
import HCSStarRatingView


class CategoryViewController: UIViewController , UITableViewDataSource 
, GMSMapViewDelegate {

@IBOutlet weak var gms: GMSMapView!

override func viewDidLoad() {
    super.viewDidLoad()

    let camera = GMSCameraPosition.camera(withLatitude: 31.529679,
                                          longitude: 34.459619,
                                          zoom: 13,
                                          bearing: 30,
                                          viewingAngle: 40)
    //Setting the googleView
    self.gms.camera = camera
    self.gms.delegate = self
    self.gms?.isMyLocationEnabled = true
    self.gms.settings.myLocationButton = true
    self.gms.settings.compassButton = true
    self.gms.settings.zoomGestures = true
    self.gms.animate(to: camera)

    //Setting the start and end location
    let origin = "\(31.529679),\(34.459619)"
    let destination = "\(31.5201027),\(34.4480504)"


    let url = "https://maps.googleapis.com/maps/api/directions/json?origin=\(origin)&destination=\(destination)&mode=driving"

    //Rrequesting Alamofire and SwiftyJSON
    Alamofire.request(url).responseJSON { response in
        print(response.request as Any)  // original URL request
        print(response.response as Any) // HTTP URL response
        print(response.data as Any)     // server data
        print(response.result)   // result of response serialization

        let json = try! JSON(data: response.data!)
        let routes = json["routes"].arrayValue

        for route in routes
        {
            let routeOverviewPolyline = route["overview_polyline"].dictionary
            let points = routeOverviewPolyline?["points"]?.stringValue
            let path = GMSPath.init(fromEncodedPath: points!)
            let polyline = GMSPolyline.init(path: path)
            polyline.strokeColor = UIColor.red
            polyline.strokeWidth = 10
            polyline.map = self.gms
        }
    }

    let marker = GMSMarker()
    marker.position = CLLocationCoordinate2D(latitude: 31.529679, 
    longitude: 34.459619)
    marker.title = "Mobiloitte"
    marker.snippet = "India"
    marker.map = gms

    //28.643091, 77.218280
    let marker1 = GMSMarker()
    marker1.position = CLLocationCoordinate2D(latitude: 31.5201027, 
    longitude: 34.4480504)
    marker1.title = "NewDelhi"
    marker1.snippet = "India"
    marker1.map = gms

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}