ARImageAnchor orientation in relation to a SCNNode

Question

My current code base provides the orientation (pitch, yaw, roll) of an ARImageAnchor in relation to the world. What I want to achieve is to get the ARImageAnchor orientation data in relation to a node that has been added sometime after starting the session.

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

     guard let _ = anchor as? ARImageAnchor else { return }
    
     DispatchQueue.main.async {

        let cylinderNode = SCNNode()
        cylinderNode.geometry = SCNCylinder(radius: 0.05, height: 0.4)
        node.addChildNode(cylinderNode)
        
        let ea: SCNVector3 = node.eulerAngles
        
        print(self.convert(ea.x), self.convert(ea.y), self.convert(ea.z))
    }
}

Any help would be much appreciated!

Answer 1

You can pass anchor's orientation part of the simd_float4x4 transform to your model (note that this data is stored in each ARFrame of the current session) restoring position:

import ARKit
import SceneKit

class ViewController : UIViewController, ARSCNViewDelegate {
    
    @IBOutlet var sceneView: ARSCNView!
    var model = SCNNode()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        sceneView.delegate = self

        sceneView.scene = SCNScene(named: "ARScene")!
        model = sceneView.scene.rootNode.childNode(withName: "model", 
                                                recursively: true)!
    }
    
    @IBAction func passTransformButton(_ sender: UIButton) {

        if let trans = sceneView.session.currentFrame?.anchors[0].transform {

            model.simdTransform = trans          // Full Transform

            model.simdTransform.columns.3.x = 0  // restore position X
            model.simdTransform.columns.3.y = 0  // restore position Y
            model.simdTransform.columns.3.z = 0  // restore position Z
        }
    }
}