Google Maps decoded GMSPath incorrect iOS

Question

So, I use the directions API in my app. However, when I decode the polyline from the response, it does not show up correctly. Here is my code:

    //Construct request URL
    NSString *urlString = [NSString stringWithFormat:
                           @"%@?origin=%f,%f&destination=%f,%f&sensor=true&key=%@",
                           @"https://maps.googleapis.com/maps/api/directions/json",
                           userMarker.position.latitude,
                           userMarker.position.longitude,
                           place.coordinate.latitude,
                           place.coordinate.longitude,
                           @"AIzaSyDrtHA-AMiVVylUPcp46_Vf1eZJJFBwRCY"];

    NSURL *directionsURL = [NSURL URLWithString:urlString];


    //Get directions in JSON format
    dispatch_async(dispatch_get_main_queue(), ^{
        NSData* data = [NSData dataWithContentsOfURL:directionsURL];

        NSError* error;

        if(data){
            NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

            //Parse JSON and plot route on map
            NSDictionary *routes = [json objectForKey:@"routes"][0];

            NSDictionary *route = [routes objectForKey:@"overview_polyline"];
            NSString *overview_route = [route objectForKey:@"points"];

            //Clear map from previous polylines
            [self.mapView clear];

            //Make polyline
            GMSPath *path = [GMSPath pathFromEncodedPath:overview_route];
            GMSPolyline *polyline = [GMSPolyline polylineWithPath:path];
            polyline.strokeWidth = 4;
            polyline.strokeColor = [UIColor darkGrayColor];
            polyline.map = self.mapView;
});

And here is the polyline:

As you can,see it does not follow the road properly. However, to me it seems as if there are not enough points to have proper bends.

EDIT: This only happens 50% of the time, sometimes it shows up correctly, sometimes it does not.

What could I be doing wrong?

Answer 1

Going by this (which is using the js API instead of the json API that you're using):

Get a polyline from Google maps directions V3

It looks like you should use the lines in each of the steps of the legs in the response, instead of the overview_polyline which is probably meant to be just a rough approximate line.