How to get image data based on ARFaceAnchor or node position?

Question

I'm trying to create a 2D face unwrap image from a live camera feed from an ARKit session.

I see there is another question about mapping an image onto a mesh. My question is different - it is about generating an image (or many smaller images) from the mesh and camera feed.

• The session detects the user's face and adds a ARFaceAnchor to the renderer.
• The anchor has a geometry object, defining a mesh
• Mesh has a large number of vertices
• For each update, there is a corresponding camera image
• Camera image has a pixel buffer with image data

How do I retrieve image data around the face anchor vertices, to "stitch" together a face unwrap from the corresponding camera frames?

var session: ARSession = self.sceneView.session

func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {
    
    if let faceAnchor = anchor as? ARFaceAnchor,
       let faceGeometry: ARSCNFaceGeometry = faceGeometry {

        if let pixelBuffer: CVPixelBuffer = session.currentFrame?.capturedImage,
           let anchors: [ARAnchor] = session.currentFrame?.anchors {
           print("how to get pixel buffer bytes around any given anchor?")
        }

        for index in 0 ..< faceGeometry.vertices.count {
            let point = faceGeometry.vertices[index]
            let position = SCNVector3(point.x, point.y, point.z)
            print("How to use this position to retrieve image data from pixel buffer around this position?")
        }
    }
}

Included is a sample of where the face geometry vertices are positioned