Face detection swift vision kit

I am trying Vision kit for iOS 11. I can use Vision and I can find boundbox values face. But I don't know how can I draw a rectangle using this points. I hope so my question is clear.

Hope you were able to use VNDetectFaceRectanglesRequest and able to detect faces. To show rectangle boxes there are lots of ways to achieve it. But simplest one would be using CAShapeLayer to draw layer on top your image for each face you detected.

Consider you have VNDetectFaceRectanglesRequest like below

let request = VNDetectFaceRectanglesRequest { [unowned self] request, error in
            if let error = error {
                // somthing is not working as expected
            }
            else {
                //  we got some face detected
                self.handleFaces(with: request)
            }
        }
        let handler = VNImageRequestHandler(ciImage: ciImage, options: [:])
        do {
            try handler.perform([request])
        }
        catch {
           // catch exception if any
        }

You can implement a simple method called handleFace for each face detected and use VNFaceObservation property to draw a CAShapeLayer.

func handleFaces(with request: VNRequest) {
        imageView.layer.sublayers?.forEach { layer in
            layer.removeFromSuperlayer()
        }
        guard let observations = request.results as? [VNFaceObservation] else {
            return
        }
        observations.forEach { observation in
            let boundingBox = observation.boundingBox
            let size = CGSize(width: boundingBox.width * imageView.bounds.width,
                              height: boundingBox.height * imageView.bounds.height)
            let origin = CGPoint(x: boundingBox.minX * imageView.bounds.width,
                                 y: (1 - observation.boundingBox.minY) * imageView.bounds.height - size.height)

            let layer = CAShapeLayer()
            layer.frame = CGRect(origin: origin, size: size)
            layer.borderColor = UIColor.red.cgColor
            layer.borderWidth = 2

            imageView.layer.addSublayer(layer)
        }
    }

More info can be found here in Github repo iOS-11-by-Examples