Face position using visionKit in ARKit - swift

Question

I added visionKit face detection on an ARSCNView, it cab detect the face, here how I did that
public func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
let faceDetectionRequest = VNDetectFaceRectanglesRequest(completionHandler: { (request: VNRequest, error: Error?) in
DispatchQueue.main.async {
self.faceLayers.forEach { drawing in
drawing.removeFromSuperlayer()
}
if let observations = request.results as? [VNFaceObservation] {
self.handleFaceDetectionObservations(observations: observations)
}
}
})
guard let capturedImage = sceneView.session.currentFrame?.capturedImage else { return }
let imageRequestHandler = VNImageRequestHandler(cvPixelBuffer: capturedImage, orientation: .leftMirrored, options: [:])
do {
try imageRequestHandler.perform([faceDetectionRequest])
} catch {
print("perform fail, error: ", error.localizedDescription)
}
}
fileprivate func handleFaceDetectionObservations(observations: [VNFaceObservation]) {
for observation in observations {
let newWidth = sceneView.bounds.width * observation.boundingBox.width
let newHeight = sceneView.bounds.height * observation.boundingBox.height
let newX = sceneView.bounds.width * observation.boundingBox.origin.x
let newY = sceneView.bounds.height * observation.boundingBox.origin.y
let faceRectConverted = CGRect(x: newX, y: newY, width: newWidth, height: newHeight)
let faceRectanglePath = CGPath(rect: faceRectConverted, transform: nil)
let faceLayer = CAShapeLayer()
faceLayer.path = faceRectanglePath
faceLayer.fillColor = UIColor.black.cgColor
self.faceLayers.append(faceLayer)
self.sceneView.layer.addSublayer(faceLayer)
}
}
The only issue that I have here is the face position in the view, it's calculated wrong. Looks like the problem come from camera mirroring, when the goes right, the face rectangular goes left, or when the face goes up, the rectangular goes down. I don't know how to do the right calculation to tie observation rect to the right place in sceneView . Could anyone help me on that!
Also have a same problem on landscape, the rectangular height is more compact there...
Thanks