ios - 如何旋转 Mapbox 地图视图的自定义标记标题（方向）

Question

如何在 Swift 上更改 Mapbox 地图上自定义标记的方向（标题）。这是我的代码

func mapView(_ mapView: MGLMapView, imageFor annotation: MGLAnnotation) -> MGLAnnotationImage? {
    var annotationImage = mapView.dequeueReusableAnnotationImage(withIdentifier: "annotation")

    if annotationImage == nil {

        var image = UIImage(named: "mapdirection")!
        image = image.withAlignmentRectInsets(UIEdgeInsets(top: 0, left: 0, bottom: image.size.height/2, right: 0))

        annotationImage = MGLAnnotationImage(image: image, reuseIdentifier: "annotation")
    }
    return annotationImage
}