ARAnchor for SCNNode - swift

Question

I'm trying to get a hold of the anchor after adding an SCNNode to the scene of an ARSCNView. My understanding is that the anchor should be created automatically, but I can't seem to retrieve it.
Below is how I add it. The node is saved in a variable called testNode.
let node = SCNNode()
node.geometry = SCNBox(width: 0.5, height: 0.1, length: 0.3, chamferRadius: 0)
node.geometry?.firstMaterial?.diffuse.contents = UIColor.green
sceneView.scene.rootNode.addChildNode(node)
testNode = node
Here is how I try to retrieve it. It always prints nil.
if let testNode = testNode {
print(sceneView.anchor(for: testNode))
}
Does it not create the anchor? If it does: is there another method I can use to retrieve it?

Answer 1

If you have a look at the Apple Docs it states that:
To track the positions and orientations of real or virtual objects
relative to the camera, create anchor objects and use the add(anchor:)
method to add them to your AR session.
As such, I think that since your aren't using PlaneDetection you would need to create an ARAnchor manually if it is needed:
Whenever you place a virtual object, always add an ARAnchor representing its position and orientation to the ARSession. After moving a virtual object, remove the anchor at the old position and create a new anchor at the new position. Adding an anchor tells ARKit that a position is important, improving world tracking quality in that area and helping virtual objects appear to stay in place relative to real-world surfaces.
You can read more about this in the following thread What's the difference between using ARAnchor to insert a node and directly insert a node?
Anyway, in order to get you started I began by creating an SCNNode called currentNode:
var currentNode: SCNNode?
Then using a UITapGestureRecognizer I created an ARAnchor manually at the touchLocation:
#objc func handleTap(_ gesture: UITapGestureRecognizer){
//1. Get The Current Touch Location
let currentTouchLocation = gesture.location(in: self.augmentedRealityView)
//2. If We Have Hit A Feature Point Get The Result
if let hitTest = augmentedRealityView.hitTest(currentTouchLocation, types: [.featurePoint]).last {
//2. Create An Anchore At The World Transform
let anchor = ARAnchor(transform: hitTest.worldTransform)
//3. Add It To The Scene
augmentedRealitySession.add(anchor: anchor)
}
}
Having added the anchor, I then used the ARSCNViewDelegate callback to create the currentNode like so:
func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
if currentNode == nil{
currentNode = SCNNode()
let nodeGeometry = SCNBox(width: 0.2, height: 0.2, length: 0.2, chamferRadius: 0)
nodeGeometry.firstMaterial?.diffuse.contents = UIColor.cyan
currentNode?.geometry = nodeGeometry
currentNode?.position = SCNVector3(anchor.transform.columns.3.x, anchor.transform.columns.3.y, anchor.transform.columns.3.z)
node.addChildNode(currentNode!)
}
}
In order to test that it works, e.g being able to log the corresponding ARAnchor, I changed the tapGesture method to include this at the end:
if let anchorHitTest = augmentedRealityView.hitTest(currentTouchLocation, options: nil).first,{
print(augmentedRealityView.anchor(for: anchorHitTest.node))
}
Which in my ConsoleLog prints:
Optional(<ARAnchor: 0x1c0535680 identifier="23CFF447-68E9-451D-A64D-17C972EB5F4B" transform=<translation=(-0.006610 -0.095542 -0.357221) rotation=(-0.00° 0.00° 0.00°)>>)
Hope it helps...