Distance between face and camera using ARKit

Question

Is there any where are you to get distance between camera and face using ARKit ?

Answer 1

I think this is possible by using the ARFaceAnchor.leftEyeTransform and ARFaceAnchor.rightEyeTransform properties.

Once you have these you can get the approximate distance of the eyes to the Camera using the worldPosition of the Eyes and subtracting the position of the Camera e.g. SCNVector3Zero.

Below is a very crude example with all the code commented so it should be easy enough to understand:

//------------------------------
// MARK: - SCNVector3 Extensions
//------------------------------

extension SCNVector3{

    ///Get The Length Of Our Vector
    func length() -> Float { return sqrtf(x * x + y * y + z * z) }

    ///Allow Us To Subtract Two SCNVector3's
    static func - (l: SCNVector3, r: SCNVector3) -> SCNVector3 { return SCNVector3Make(l.x - r.x, l.y - r.y, l.z - r.z) }
}

//--------------------------
// MARK: - ARSCNViewDelegate
//--------------------------

extension ViewController: ARSCNViewDelegate{

    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

        //1. Setup The FaceNode & Add The Eyes
        faceNode = node
        faceNode.addChildNode(leftEye)
        faceNode.addChildNode(rightEye)
        faceNode.transform = node.transform

        //2. Get The Distance Of The Eyes From The Camera
        trackDistance()
    }

    func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {

        faceNode.transform = node.transform

        //2. Check We Have A Valid ARFaceAnchor
        guard let faceAnchor = anchor as? ARFaceAnchor else { return }

        //3. Update The Transform Of The Left & Right Eyes From The Anchor Transform
        leftEye.simdTransform = faceAnchor.leftEyeTransform
        rightEye.simdTransform = faceAnchor.rightEyeTransform

        //4. Get The Distance Of The Eyes From The Camera
        trackDistance()
    }


    /// Tracks The Distance Of The Eyes From The Camera
    func trackDistance(){

        DispatchQueue.main.async {

            //4. Get The Distance Of The Eyes From The Camera
            let leftEyeDistanceFromCamera = self.leftEye.worldPosition - SCNVector3Zero
            let rightEyeDistanceFromCamera = self.rightEye.worldPosition - SCNVector3Zero

            //5. Calculate The Average Distance Of The Eyes To The Camera
            let averageDistance = (leftEyeDistanceFromCamera.length() + rightEyeDistanceFromCamera.length()) / 2
            let averageDistanceCM = (Int(round(averageDistance * 100)))
            print("Approximate Distance Of Face From Camera = \(averageDistanceCM)")
        }
    }
}

class ViewController: UIViewController{

    @IBOutlet var sceneView: ARSCNView!

    var faceNode = SCNNode()
    var leftEye = SCNNode()
    var rightEye = SCNNode()

    //-----------------------
    // MARK: - View LifeCycle
    //-----------------------

    override func viewDidLoad() {
        super.viewDidLoad()

        //1. Set Up Face Tracking
        guard ARFaceTrackingConfiguration.isSupported else { return }
        let configuration = ARFaceTrackingConfiguration()
        configuration.isLightEstimationEnabled = true
        sceneView.delegate = self
        sceneView.showsStatistics = true
        sceneView.session.run(configuration, options: [.resetTracking, .removeExistingAnchors])

        //2. Setup The Eye Nodes
        setupEyeNode()
    }

    override func viewWillAppear(_ animated: Bool) { super.viewWillAppear(animated) }

    //-----------------------
    // MARK: - Eye Node Setup
    //-----------------------

    /// Creates To SCNSpheres To Loosely Represent The Eyes
    func setupEyeNode(){

        //1. Create A Node To Represent The Eye
        let eyeGeometry = SCNSphere(radius: 0.005)
        eyeGeometry.materials.first?.diffuse.contents = UIColor.cyan
        eyeGeometry.materials.first?.transparency = 1

        //2. Create A Holder Node & Rotate It So The Gemoetry Points Towards The Device
        let node = SCNNode()
        node.geometry = eyeGeometry
        node.eulerAngles.x = -.pi / 2
        node.position.z = 0.1

        //3. Create The Left & Right Eyes
        leftEye = node.clone()
        rightEye = node.clone()
    }

}

Hope it helps...