iOS MapKit Custom User location heading wrong

Question

I am trying to make a custom "user location" pin, with heading rotation based on users location heading.

I used this answer: https://stackoverflow.com/a/58363556/894671 as a base and managed to get up and running a custom pin, that rotates based on the heading.

The problem:

While testing on a device, it seems, that the transformation using the provided heading is not correct. Only at 0/360 degrees it shows up correctly, but If I rotate around, I am seeing default MKMapKit shown heading to be correctly rotating, while my custom icon manages to rotate twice in that same time.

Please see the attached video: https://i.imgur.com/3PEm2MS.mp4

Demo uploaded here: https://github.com/GuntisTreulands/Demo123

But for all intents and purposes, here is AnnotationView:

class AnnotationView : MKAnnotationView, HeadingDelegate {
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
    }

    func headingChanged(_ heading: CLLocationDirection) {
        // For simplicity the affine transform is done on the view itself
        UIView.animate(withDuration: 0.1, animations: { [unowned self] in
            self.transform = CGAffineTransform(rotationAngle: CGFloat(heading * .pi / 180.0 ))
        })
    }
}

and heading is forwarded from here:

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation])
    {
        if let lastLocation = locations.last {
            userLocationAnnotation.coordinate = lastLocation.coordinate
        }
    }

I can't figure out, why my location heading is acting so weird.

Answer 1

Okay, I managed to kinda solve this.

Here is the new result: https://i.sstatic.net/NHSvY.jpg

What I did was:

func locationManager(_ manager: CLLocationManager, didUpdateHeading newHeading: CLHeading) {

        if let heading = mapView.userLocation.heading {
            userLocationAnnotation.heading = -mapView.camera.heading + (heading.trueHeading > 0 ? heading.trueHeading : heading.magneticHeading)
        } else {
            userLocationAnnotation.heading = -mapView.camera.heading + (newHeading.trueHeading > 0 ? newHeading.trueHeading : newHeading.magneticHeading)
        }
    }

So - in case I am using userlocation with trackingmode == .followWithHeading, this is working great. My icon is on top of the original icon.

To hide original user icon and show yours instead - return a custom annotation view (with nothing to render) for userlocation:

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {

        guard !(annotation is MKUserLocation) else {

            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: "AnnotationView")

            if annotationView == nil {
                annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: "AnnotationView")
            }

            return annotationView
        }

        if let annotation = annotation as? Annotation {
            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: NSStringFromClass(Annotation.self))
            if (annotationView == nil) {
                annotationView = AnnotationView(annotation: annotation as MKAnnotation, reuseIdentifier: NSStringFromClass(Annotation.self))
            } else {
                annotationView!.annotation = annotation as MKAnnotation
            }

                annotation.headingDelegate = annotationView as? HeadingDelegate
                annotationView!.image = UIImage.init(named: "user_pin")

            return annotationView
        }
        
        return nil
    }

Thus the result is:

1.) Get original apple maps user location + followWithHeading, but with a custom pin and correct location.

2.) I can adjust my custom location pin location to some different coordinates, but keep in mind, that followWithHeading will rotate around the real userLocation coordinates.

3.) I have also noticed, that without userlocation, the original calculation:

userLocationAnnotation.heading = -mapView.camera.heading + (newHeading.trueHeading > 0 ? newHeading.trueHeading : newHeading.magneticHeading)

Is also .. kinda okay, if I move and rotate. It is faulty, if I just rotate in place. Still cannot solve that one.

I also managed to make a custom followWithHeading, with this function:

func locationManager(_ manager: CLLocationManager, didUpdateHeading newHeading: CLHeading) {

        mapView.centerCoordinate = userLocationAnnotation.coordinate
            
        mapView.camera.heading = (newHeading.trueHeading > 0 ? newHeading.trueHeading : newHeading.magneticHeading)

        userLocationAnnotation.heading = -mapView.camera.heading + (newHeading.trueHeading > 0 ? newHeading.trueHeading : newHeading.magneticHeading)

    }

But the result is not as fluid as the original apple map rotation. If I rotate fast, then it is fine. But if I slowly turn my device, then the rotation is visibly not smooth.

See the result: https://i.sstatic.net/RtkeG.jpg