How to get accurate route for map - ios

Question

I'm trying to build a route using Google Directions API. It returns an array of waypoints, however, the number of waypoints is not enough to build a smoothed route, and as the result I receive quite inaccurate route what is super crucial and inappropriate for transport application. I also tried HERE maps, almost the same result.
Is there any other services that may build more accurate route, or any solution applicable to the Google Directions API?
Here is the function:
public func getWaypoints(startLocation: [Double]!, endLocation: [Double]!, mode:String? = "walking", lang:String? = "en") -> [Dictionary<String,Any>] {
var resultedArray:[Dictionary<String,Any>] = []
let routeGM = Just.get("https://maps.googleapis.com/maps/api/directions/json?", params: ["origin":"\(startLocation[0]),\(startLocation[1])", "destination": "\(endLocation[0]),\(endLocation[1])", "mode": mode!, "key":self.KEY, "language": lang!])
if let _ = routeGM.error {
} else {
do {
if let data = jsonToNSData(routeGM.json! as AnyObject), let jsonData = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? NSDictionary {
let status = jsonData["status"] as! String
if(status == "OK") {
let results = jsonData["routes"] as! Array<Dictionary<String, AnyObject>>
let legs = results[0]["legs"] as! Array<Dictionary<String, AnyObject>>
let steps = legs[0]["steps"] as! Array<Dictionary<String, AnyObject>>
for i in 0...steps.count-1 {
let item = steps[i]
let start = item["start_location"] as! Dictionary<String,Any>
let end = item["end_location"] as! Dictionary<String,Any>
resultedArray.append(["start_location_lat": start["lat"]!,"start_location_lng": start["lng"]!,"end_location_lat": end["lat"]!,"end_location_lng": end["lng"]!])
}
}
else {
print("not found")
}
}
} catch {
print(error)
}
}
return resultedArray
}
Calling function:
func buildRoute(startCoord:[Double]!, endCoord:[Double]!) {
DispatchQueue.global(qos: .background).async {
let route:[Dictionary<String,Any>] = self.GMSRequest.getWaypoints(startLocation: startCoord,endLocation: endCoord, mode: "driving")
DispatchQueue.main.async {
let path = GMSMutablePath()
for item in route {
path.add(CLLocationCoordinate2D(latitude: item["start_location_lat"]! as! CLLocationDegrees, longitude: item["start_location_lng"]! as! CLLocationDegrees))
path.add(CLLocationCoordinate2D(latitude: item["end_location_lat"]! as! CLLocationDegrees, longitude: item["end_location_lng"]! as! CLLocationDegrees))
}
// Create the polyline, and assign it to the map.
self.polyline.path = path
self.polyline.strokeColor = Styles.colorWithHexString("#3768CD")
self.polyline.strokeWidth = 3.0
self.polyline.geodesic = true
self.polyline.map = self.mapView
}
}
}