Unable to differentiate between plane detected by ARKit and a digital object to be placed using HitTest - swift

Question

I'm fairly new to iOS Swift programming. I'm using ARKit to build a very basic app to detect a horizontal plane and place,translate,rotate,modify or delete an object on it.
My main concern is to differential between the plane detected by ARKit and a digital object that I've placed. My thinking was to use hitTest(:options:) to select the object (if any) and hitTest(:types:) to select the plane through a tap gesture. I'm attaching the relevant code snippet below.
#objc func tapped(_ gesture: UITapGestureRecognizer){
let sceneView = gesture.view as! ARSCNView
let location = gesture.location(in: sceneView)
let hitTestOptions: [SCNHitTestOption: Any] = [.boundingBoxOnly: true]
let existingNodeHitTest = sceneView.hitTest(location, options: hitTestOptions)
if let existingNode = existingNodeHitTest.first?.node {
// Move, rotate, modify or delete the object
} else {
// Option to add other objects
let hitTest = sceneView.hitTest(location, types: .existingPlaneUsingExtent)
if !hitTest.isEmpty {
let node = findNode(at: location)
if node !== selectedNode {
self.addItems(hitTestResult: hitTest.first!)
}
}
}
}
func addItems(hitTestResult: ARHitTestResult) {
let scene = SCNScene(named: "BuildingModels.scnassets/model/model.scn")
let itemNode = (scene?.rootNode.childNode(withName: "SketchUp", recursively: false))!
let transform = hitTestResult.worldTransform
let position = SCNVector3(transform.columns.3.x,transform.columns.3.y,transform.columns.3.z)
itemNode.position = position
// self.sceneView.scene.lightingEnvironment.contents = scene.lightingEnvironment.contents
self.sceneView.scene.rootNode.addChildNode(itemNode)
selectedNode = itemNode
}
func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
guard let planeAnchor = anchor as? ARPlaneAnchor else {return}
let gridNode = createGrid(planeAnchor: planeAnchor)
node.addChildNode(gridNode)
}
func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {
guard let planeAnchor = anchor as? ARPlaneAnchor else {return}
node.enumerateChildNodes { (childNode, _) in
childNode.removeFromParentNode()
}
let gridNode = createGrid(planeAnchor: planeAnchor)
node.addChildNode(gridNode)
}
When I run the code, the hitTest(_:options:) returns the plane detected. Are there any ways to select only the SCNNodes (objects) that I place and not the plane detected. Am I missing something? Any help is highly appreciated.
Thanks,
Sourabh.

Answer 1

Looking at your question you are already half way there.
The way to handle this in it's entirety, is to make use of the following HitTest functions within your UITapGestureRecognizer function:
(1) An ARSCNHitTest which:
Searches for real-world objects or AR anchors in the captured camera image corresponding to a point in the SceneKit view.
(2) AnSCNHitTest which:
Looks for SCNGeometry objects along the ray you specify. For each intersection between the ray and and a geometry, SceneKit creates a hit-test result to provide information about both the SCNNode object containing the geometry and the location of the intersection on the geometry’s surface.
Using your UITapGestureRecognizer as an example therefore, you can differentiate between an ARPlaneAnchor (detectedPlane) and any SCNNode within your scene like so:
#objc func handleTap(_ gesture: UITapGestureRecognizer){
//1. Get The Current Touch Location
let currentTouchLocation = gesture.location(in: self.augmentedRealityView)
//2. Perform An ARNSCNHitTest To See If We Have Hit An ARPlaneAnchor
if let planeHitTest = augmentedRealityView.hitTest(currentTouchLocation, types: .existingPlane).first,
let planeAnchor = planeHitTest.anchor as? ARPlaneAnchor{
print("User Has Tapped On An Existing Plane = \(planeAnchor.identifier)")
return
}
//3. Perform An SCNHitTest To See If We Have Hit An SCNNode
if let nodeHitTest = augmentedRealityView.hitTest(currentTouchLocation, options: nil).first {
let nodeTapped = nodeHitTest.node
print("An SCNNode Has Been Tapped = \(nodeTapped)")
return
}
}
If you make use of the name property for any of your SCNNode’s this will also help you further e.g:
if let name = nodeTapped.name{
print("An SCNNode Named \(name) Has Been Tapped")
}
Additionally, if you ONLY want to detect objects you have added e.g SCNNodes then you can simply remove part two of the getureRecognizer function.
Hope it helps...

Answer 2

To fix this issue, you should loop through your scene nodes, after that you can manipulate with your wanted node. Example:
for node in sceneView.scene.rootNode.childNodes {
if node.name == "yorNodeName" {
// do your manipulations
}
}
Don't forget to add name to your nodes. Example:
node.name = "yorNodeName"
I hope it helped!