如何使用swift将图像数据和GPS元数据写入保存的相册？

Question

我正在尝试使用自定义相机应用程序为我拍摄的图像添加GPS元数据。我的相机应用程序按预期拍摄图像，每张照片中都包含许多苹果特定的元数据值。但是我似乎无法添加GPS数据。我做错了什么？谢谢。

class ViewController: UIViewController {

  var output : AVCaptureStillImageOutput!
  var locationManager : CLLocationManager()

  override func viewDidLoad()
    createCamera()
    initLocationManager()

    super.viewDidLoad()
  }

  func createCamera(){
  //create camera code.  works fine
  }

  func takePhoto(){
    self.output.captureStillImageAsynchronousFromConnection(self.connection){
      buffer, error in
      if let error = error{
        println("Error: \(error)")
      }
      else{
        var imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(buffer)
        var metadata = self.getImageMetaData()
        var library = ALAssestsLibrary()
        library.writeImageDataToSavedPhotosAlbum(imageData, metadata, completionBlock: {
          (assetURL: NSURL!, error: NSError!) -> Void in

          })
       }
     }
  }

  func getImageMetadata() -> NSMutableDictionary{

    var locDict = NSMutableDictioary()
    locDict.setObject(self.locationManager.location.timestamp, forKey: "KCGImagePrropertyGPSTimeStamp")
    locDict.setObject("N", forKey: kCGImagePropertyGPSLatitudeRef")
    locDict.setObject(self.locationManager.location.coordinate.latitude, forKey: "kCGImagePropertyGPSLatitude")
    locDict.setObject("W", forKey: "kCGImagePropertyGPSLongitudeRef")
    locDict.setObject(self.locationManager.location.coordinate.longitude, forKey: "kCGImagePropertyGPSLongitude")

    return locDict
    //this returns the correct coordinates
    //NOTE: I hard coded the Ref values for brevity.
  }
}

注意：我使用ExifTool来查看元数据。