VisionCoreMLTextDrawRectangle.swift

func drawRectanglesOnObservations(observations : [VNDetectedObjectObservation]){
        DispatchQueue.main.async {
            guard let image = self.imageView.image
                else{
                    print("Failure in retrieving image")
                    return
            }
            let imageSize = image.size
            var imageTransform = CGAffineTransform.identity.scaledBy(x: 1, y: -1).translatedBy(x: 0, y: -imageSize.height)
            imageTransform = imageTransform.scaledBy(x: imageSize.width, y: imageSize.height)
            UIGraphicsBeginImageContextWithOptions(imageSize, true, 0)
            let graphicsContext = UIGraphicsGetCurrentContext()
            image.draw(in: CGRect(origin: .zero, size: imageSize))
            
            graphicsContext?.saveGState()
            graphicsContext?.setLineJoin(.round)
            graphicsContext?.setLineWidth(8.0)
            
            graphicsContext?.setFillColor(red: 0, green: 1, blue: 0, alpha: 0.3)
            graphicsContext?.setStrokeColor(UIColor.green.cgColor)
            
            
            
            var previousString = ""
            let elements = ["VISION","COREML"]
            
            observations.forEach { (observation) in
                
                var string = observationStringLookup[observation as! VNTextObservation] ?? ""
                let tempString = string
                string = string.replacingOccurrences(of: previousString, with: "")
                string = string.trim()
                previousString = tempString
                
                if elements.contains(where: string.contains){
                    
                    let observationBounds = observation.boundingBox.applying(imageTransform)
                    graphicsContext?.addRect(observationBounds)
                }
                
                
            }
            graphicsContext?.drawPath(using: CGPathDrawingMode.fillStroke)
            graphicsContext?.restoreGState()
            
            let drawnImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
            self.imageView.image = drawnImage
            
        }
    }