How to rotate a 3D model in a USDZ file programmatically in Swift?

Question

I currently have my app detecting a postcard picture. Once detected I place a 3D model of a dog on top of it. Problem is, the model is currently having the back of the dog sit sitting the card rather than it’s feet.

Is there a way to programmatically rotate the model so that the feet is standing on the postcard?

class ViewController: UIViewController, ARSCNViewDelegate {
    
    @IBOutlet var sceneView: ARSCNView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        sceneView.delegate = self
    }
    
//MARK-: WHERE I CONFIGURE MY APP TO DETECT AN IMAGE

    override func viewWillAppear(_ animated: Bool) {
            super.viewWillAppear(animated)
            
            let configuration = ARImageTrackingConfiguration()
            
            guard let trackedImages = ARReferenceImage.referenceImages(inGroupNamed: "Photos", bundle: Bundle.main) else {
                print("No images available")
                return
            }
            
            configuration.trackingImages = trackedImages
            configuration.maximumNumberOfTrackedImages = 7
            
            sceneView.session.run(configuration)
    }
    
//MARK-: WHERE I PLACE A PLANE/DOG MODEL (named: shipScene) OVER THE DETECTED IMAGE

     func renderer(_ renderer: SCNSceneRenderer, nodeFor anchor: ARAnchor) -> SCNNode? {
            
            let node = SCNNode()
            
            if let imageAnchor = anchor as? ARImageAnchor {
                let plane = SCNPlane(width: imageAnchor.referenceImage.physicalSize.width, height: imageAnchor.referenceImage.physicalSize.height)

                plane.firstMaterial?.diffuse.contents = UIColor(white: 1, alpha: 0.8)

                let planeNode = SCNNode(geometry: plane)
                planeNode.eulerAngles.x = -.pi / 2

                guard let url = Bundle.main.url(forResource: "shipScene", withExtension: "usdz") else { fatalError() }
                let mdlAsset = MDLAsset(url: url)
                let dogScene = SCNScene(mdlAsset: mdlAsset)
                let dogNode = shipScene.rootNode.childNodes.first!

                shipNode.position = SCNVector3Zero
                shipNode.position.z = 0.15
                
                planeNode.addChildNode(shipNode)
                node.addChildNode(planeNode)
            }
            
            return node
    }
    
}

I figure I can use a rendition of

shipNode.position.x

To move the model, but any attempts has just moved the model around (but not rotating it).

Answer 1

At first you have to retrieve a model node from scene. Take into account that node's name is not the same as scene's name! You can find your node in Scene graph hierarchy.

let model = scene.rootNode.childNode(withName: "myModel", recursively: true)!

Then you can rotate it using rotation property:

model.rotation.y = -CGFloat.pi / 2

or using eulerAngles property:

model.eulerAngles = SCNVector3(0, -CGFloat.pi/2, 0)

or using orientation property:

model.orientation = SCNVector4(0, 1, 0, -CGFloat.pi/2)

Pay attention where a pivot point of your node is. A rotation should be around the pivot point.