在 iOS 上使用 ML Kit 辨識地標

可以使用 ML Kit 辨識圖片中的知名地標。

事前準備

  1. 如果尚未將 Firebase 加入應用程式,請按照下列步驟操作: 入門指南中的步驟。
  2. 在 Podfile 中加入 ML Kit 程式庫:
    pod 'Firebase/MLVision', '6.25.0'
    
    敬上 安裝或更新專案的 Pod 後,請務必開啟 Xcode 專案 .xcworkspace
  3. 在應用程式中匯入 Firebase:

    Swift

    import Firebase

    Objective-C

    @import Firebase;
  4. 如果您尚未為專案啟用雲端式 API,請先啟用 現在:

    1. 開啟 ML Kit Firebase 控制台的 API 頁面
    2. 如果您尚未將專案升級至 Blaze 定價方案,請按一下 如要這麼做,請升級。(只有在您的 專案並未採用 Blaze 方案)。

      只有 Blaze 層級的專案可以使用以雲端為基礎的 API。

    3. 如果尚未啟用雲端式 API,請按一下「Enable Cloud-based API」(啟用雲端式 API) API
    ,瞭解如何調查及移除這項存取權。

設定地標偵測工具

根據預設,Cloud 偵測工具會使用模型的穩定版本 最多會傳回 10 筆結果。如要變更下列任一設定 可以使用 VisionCloudDetectorOptions 物件來指定這些 Pod 的 在以下範例中:

Swift

let options = VisionCloudDetectorOptions()
options.modelType = .latest
options.maxResults = 20

Objective-C

  FIRVisionCloudDetectorOptions *options =
      [[FIRVisionCloudDetectorOptions alloc] init];
  options.modelType = FIRVisionCloudModelTypeLatest;
  options.maxResults = 20;
  

在下一個步驟中,請傳遞 VisionCloudDetectorOptions 物件。

執行地標偵測工具

如要辨識圖片中的地標,請以 UIImageCMSampleBufferRefVisionCloudLandmarkDetectordetect(in:) 方法:

  1. 取得 VisionCloudLandmarkDetector 的執行個體:

    Swift

    lazy var vision = Vision.vision()
    
    let cloudDetector = vision.cloudLandmarkDetector(options: options)
    // Or, to use the default settings:
    // let cloudDetector = vision.cloudLandmarkDetector()

    Objective-C

    FIRVision *vision = [FIRVision vision];
    FIRVisionCloudLandmarkDetector *landmarkDetector = [vision cloudLandmarkDetector];
    // Or, to change the default settings:
    // FIRVisionCloudLandmarkDetector *landmarkDetector =
    //     [vision cloudLandmarkDetectorWithOptions:options];
  2. 使用 UIImageVisionImage CMSampleBufferRef

    如何使用 UIImage

    1. 視需要旋轉圖片,使其 imageOrientation 屬性為 .up
    2. 使用正確旋轉的做法建立 VisionImage 物件 UIImage。請勿指定任何輪替中繼資料 (預設值) 值 (.topLeft),則必須使用。

      Swift

      let image = VisionImage(image: uiImage)

      Objective-C

      FIRVisionImage *image = [[FIRVisionImage alloc] initWithImage:uiImage];

    如何使用 CMSampleBufferRef

    1. 建立 VisionImageMetadata 物件,以指定 包含的圖片資料方向 CMSampleBufferRef 緩衝區。

      如何取得圖片方向:

      Swift

      func imageOrientation(
          deviceOrientation: UIDeviceOrientation,
          cameraPosition: AVCaptureDevice.Position
          ) -> VisionDetectorImageOrientation {
          switch deviceOrientation {
          case .portrait:
              return cameraPosition == .front ? .leftTop : .rightTop
          case .landscapeLeft:
              return cameraPosition == .front ? .bottomLeft : .topLeft
          case .portraitUpsideDown:
              return cameraPosition == .front ? .rightBottom : .leftBottom
          case .landscapeRight:
              return cameraPosition == .front ? .topRight : .bottomRight
          case .faceDown, .faceUp, .unknown:
              return .leftTop
          }
      }

      Objective-C

      - (FIRVisionDetectorImageOrientation)
          imageOrientationFromDeviceOrientation:(UIDeviceOrientation)deviceOrientation
                                 cameraPosition:(AVCaptureDevicePosition)cameraPosition {
        switch (deviceOrientation) {
          case UIDeviceOrientationPortrait:
            if (cameraPosition == AVCaptureDevicePositionFront) {
              return FIRVisionDetectorImageOrientationLeftTop;
            } else {
              return FIRVisionDetectorImageOrientationRightTop;
            }
          case UIDeviceOrientationLandscapeLeft:
            if (cameraPosition == AVCaptureDevicePositionFront) {
              return FIRVisionDetectorImageOrientationBottomLeft;
            } else {
              return FIRVisionDetectorImageOrientationTopLeft;
            }
          case UIDeviceOrientationPortraitUpsideDown:
            if (cameraPosition == AVCaptureDevicePositionFront) {
              return FIRVisionDetectorImageOrientationRightBottom;
            } else {
              return FIRVisionDetectorImageOrientationLeftBottom;
            }
          case UIDeviceOrientationLandscapeRight:
            if (cameraPosition == AVCaptureDevicePositionFront) {
              return FIRVisionDetectorImageOrientationTopRight;
            } else {
              return FIRVisionDetectorImageOrientationBottomRight;
            }
          default:
            return FIRVisionDetectorImageOrientationTopLeft;
        }
      }

      然後,建立中繼資料物件:

      Swift

      let cameraPosition = AVCaptureDevice.Position.back  // Set to the capture device you used.
      let metadata = VisionImageMetadata()
      metadata.orientation = imageOrientation(
          deviceOrientation: UIDevice.current.orientation,
          cameraPosition: cameraPosition
      )

      Objective-C

      FIRVisionImageMetadata *metadata = [[FIRVisionImageMetadata alloc] init];
      AVCaptureDevicePosition cameraPosition =
          AVCaptureDevicePositionBack;  // Set to the capture device you used.
      metadata.orientation =
          [self imageOrientationFromDeviceOrientation:UIDevice.currentDevice.orientation
                                       cameraPosition:cameraPosition];
    2. 請使用VisionImage CMSampleBufferRef 物件和輪替中繼資料:

      Swift

      let image = VisionImage(buffer: sampleBuffer)
      image.metadata = metadata

      Objective-C

      FIRVisionImage *image = [[FIRVisionImage alloc] initWithBuffer:sampleBuffer];
      image.metadata = metadata;
  3. 接著,將圖片傳遞至 detect(in:) 方法:

    Swift

    cloudDetector.detect(in: visionImage) { landmarks, error in
      guard error == nil, let landmarks = landmarks, !landmarks.isEmpty else {
        // ...
        return
      }
    
      // Recognized landmarks
      // ...
    }

    Objective-C

    [landmarkDetector detectInImage:image
                         completion:^(NSArray<FIRVisionCloudLandmark *> *landmarks,
                                      NSError *error) {
      if (error != nil) {
        return;
      } else if (landmarks != nil) {
        // Got landmarks
      }
    }];

取得可辨識的地標相關資訊

如果地標辨識成功,系統會傳回 VisionCloudLandmark 陣列 傳遞到完成處理常式在每個物件中,您可以 圖片中辨識出的地標相關資訊。

例如:

Swift

for landmark in landmarks {
  let landmarkDesc = landmark.landmark
  let boundingPoly = landmark.frame
  let entityId = landmark.entityId

  // A landmark can have multiple locations: for example, the location the image
  // was taken, and the location of the landmark depicted.
  for location in landmark.locations {
    let latitude = location.latitude
    let longitude = location.longitude
  }

  let confidence = landmark.confidence
}

Objective-C

for (FIRVisionCloudLandmark *landmark in landmarks) {
   NSString *landmarkDesc = landmark.landmark;
   CGRect frame = landmark.frame;
   NSString *entityId = landmark.entityId;

   // A landmark can have multiple locations: for example, the location the image
   // was taken, and the location of the landmark depicted.
   for (FIRVisionLatitudeLongitude *location in landmark.locations) {
     double latitude = [location.latitude doubleValue];
     double longitude = [location.longitude doubleValue];
   }

   float confidence = [landmark.confidence floatValue];
}

後續步驟