How to place 3D object (.scn file) on detected vertical plane which should be parallel to plane in ARKIt?

Question

I am going to detect horizontal and vertical plane in ARKit. After detecting whether it is horizontal or vertical surface, respectively add plane of gray color on detected surface.On tap on detected plane I am going to add 3D object of .scn file.

My code is working fine for placing 3D object (.scn file) on horizontal plane but not working correctly with vertical plane.

3D object (.scn file) for vertical plane like photo frame is facing right in SceneKit editor. So I changed it’s EularAngleY to -0 and it’s facing front now in SceneKit Editor. When I tap on detected vertical plane which is facing to front then also photo frame is facing to right and If I move device facing right and place photo frame then it’s correct.

I want to place 3D object .scn file which should be parallel to plane (If vertical plane is facing front then it should be face front even in .scn file it faces to any direction).That 3D object is not parallel to detected plane.

Have I needed to change rotation also with respect to detected plane’s angle or need to do any changes in .scn file in SceneKit editor? How can I achieve it?

Please check below code on hitting detected vertical plane. Is there anything wrong?

@objc func addObjectToSceneView1(withGestureRecognizer recognizer: UIGestureRecognizer){
    let tapLocation = recognizer.location(in: sceneView)
    let hitTestResults = sceneView.hitTest(tapLocation, types: .existingPlaneUsingExtent)

    guard let hitTestResult = hitTestResults.first, let anchor = hitTestResult.anchor as? ARPlaneAnchor else { return }


    let translation = hitTestResult.worldTransform.columns.3

    let x = translation.x
    let y = translation.y
    let z = translation.z

    guard let shipScene = SCNScene(named: "art.scnassets/frame/frame.scn"),
        let shipNode = shipScene.rootNode.childNode(withName: "frame", recursively: true)
        else { return }

    shipNode.position = SCNVector3(x,y,z)

    sceneView.scene.rootNode.addChildNode(shipNode)
}

.scn file is like below. Is this .scn file correct? Or x should be with frame's depth? Everytime whenever I tap on plane it will show image like this only.

beyowulf beyowulf · Accepted Answer · 2019-05-27T13:17:29

As I mentioned in the answer here, it is better to add an ARAnchor to the ARSession rather than directly adding an SCNNode into the scene graph after doing a hit test. Currently the code you posted doesn't take into account the rotation of the detected plane. For the code to work you would need to determine the normal of the detected plane take the dot product and cross product with the desired orientation of the model calculate the rotation, then apply the rotation. However, the ARSession will do all of that for you. By using ARAnchor(transform: hitTestResult.worldTransform) the rotation is encoded into the anchor. So you will only need to deal with transformations with the models own local coordinate space.

For example:

@objc func addObjectToSceneView1(withGestureRecognizer recognizer: UIGestureRecognizer){
    let tapLocation = recognizer.location(in: sceneView)
    let hitTestResults = sceneView.hitTest(tapLocation, types: .existingPlaneUsingExtent)

    guard let hitTestResult = hitTestResults.first, let anchor = hitTestResult.anchor as? ARPlaneAnchor else { return }
    // create anchor and add to session and wait for callback
    let anchor = ARAnchor(transform: hitTestResult.worldTransform)
    sceneView.session.add(anchor: anchor)
}

Then in your session delegate call back:

func renderer(_ renderer: SCNSceneRenderer, nodeFor anchor: ARAnchor) -> SCNNode? {
    if anchor is ARPlaneAnchor {
        // node for plane anchor
        let anchorNode = SCNNode()
        return anchorNode
    } else {
        // must be node for most recent hit test
        guard let frameScene = SCNScene(named: "art.scnassets/frame/frame.scn"),
              let frameNode = frameScene.rootNode.childNode(withName: "frame", recursively: true) else { return nil }
        return frameNode
    }
}

In you're scn file you'll want the model to be located at the origin laying flat without any transforms. This means you'll likely need to nest nodes and position the underlying model relative to a parent empty node.

Here "frame" is the outer node with no transform that is returned from nodeForAnchor and "picture" is rotated to be flat and scaled to the size of the content.

Final result:

How to place 3D object (.scn file) on detected vertical plane which should be parallel to plane in ARKIt?

1 Answers