How to save face mesh coordinates into a file

Question

I am using my iPad to code using the swift playgrounds. I have the following code. I would like to remove the face and display only the face mesh but I am not sure how to do it. Also, I would like to save the face mesh coordinates to a file if possible. It would be great if someone could help.

extension ARViewController: ARSCNViewDelegate{

    func renderer(_ renderer: SCNSceneRenderer, 
              nodeFor anchor: ARAnchor) -> SCNNode? {

        guard let faceAnchor = anchor as? ARFaceAnchor, 
              let device = arView.device 
        else { return nil }

        let faceGeometry = ARSCNFaceGeometry(device: device)

        let node = SCNNode(geometry: faceGeometry)

        node.geometry?.firstMaterial?.fillMode = .lines

        return node    
    }

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

        guard let faceAnchor = anchor as? ARFaceAnchor, 
              let faceGeometry = node.geometry as? ARSCNFaceGeometry 
        else { return }

        faceGeometry.update(from: faceAnchor.geometry)  
    }    
}

PlaygroundPage.current.liveView = ARViewController()
PlaygroundPage.current.needsIndefiniteExecution = true