Convert VNRectangleObservation points to other coordinate system

I assume you use layer for the camera, and the layer is AVCaptureVideoPreviewLayer. (https://developer.apple.com/documentation/avfoundation/avcapturevideopreviewlayer). So if you want to convert single point, use this function:layerPointConverted (https://developer.apple.com/documentation/avfoundation/avcapturevideopreviewlayer/1623502-layerpointconverted). Please notices that the y is inverted because of the VNRectangleObservation coordinates system.

let convertedTopLeft: CGPoint = cameraLayer.layerPointConverted(fromCaptureDevicePoint: CGPoint(x: rectangle.topLeft.x, y: 1 - rectangle.topLeft.y))
let convertedTopRight: CGPoint = cameraLayer.layerPointConverted(fromCaptureDevicePoint: CGPoint(x: rectangle.topRight.x, y: 1 - rectangle.topRight.y))
let convertedBottomLeft: CGPoint = cameraLayer.layerPointConverted(fromCaptureDevicePoint: CGPoint(x: rectangle.bottomLeft.x, y: 1 - rectangle.bottomLeft.y))
let convertedBottomRight: CGPoint = cameraLayer.layerPointConverted(fromCaptureDevicePoint: CGPoint(x: rectangle.bottomRight.x, y: 1 - rectangle.bottomRight.y))

Hope it helped

That was simply a matter of applying the transform to the CGPoint itself where size is the CGSize of the destination view for which I need transpose the four points.

    let transform = CGAffineTransform.identity
        .scaledBy(x: 1, y: -1)
        .translatedBy(x: 0, y: -size.height)
        .scaledBy(x: size.width, y: size.height)

    let convertedTopLeft = rectangle.topLeft.applying(transform)
    let convertedTopRight = rectangle.topRight.applying(transform)
    let convertedBottomLeft = rectangle.bottomLeft.applying(transform)
    let convertedBottomRight = rectangle.bottomRight.applying(transform)

@mihaicris answer works, but only in portrait mode. In landscape, we need to do it a little different.

if UIApplication.shared.statusBarOrientation.isLandscape {
    transform = CGAffineTransform.identity
        .scaledBy(x: -1, y: 1)
        .translatedBy(x: -size.width, y: 0)
        .scaledBy(x: size.width, y: size.height)
} else {
    transform = CGAffineTransform.identity
        .scaledBy(x: 1, y: -1)
        .translatedBy(x: 0, y: -size.height)
        .scaledBy(x: size.width, y: size.height)
}

let convertedTopLeft = rectangle.topLeft.applying(transform)
let convertedTopRight = rectangle.topRight.applying(transform)
let convertedBottomLeft = rectangle.bottomLeft.applying(transform)
let convertedBottomRight = rectangle.bottomRight.applying(transform)