How to limit SCNNode from moving when camera moves along the x-axis?

Question

I'm working a simple app using ARKit where a user can tap their screen and place a node (SCNNode) on a given location. I want the user to be able to place nodes that stay in place no matter where the camera is so that when they pan back to the location where they placed the node, it's still there.

I've gotten the tap functionality to work, but I've noticed that when I physically move my device along the x-axis, the placed node moves along with it. I've tried to anchor the nodes to something other than the root node, but it hasn't worked as expected. I tried to look up documentation on how the root node is placed and if it's calculated based on the camera which would explain why the nodes are moving along with the camera, but no luck there either.

Here's the code for placing the nodes. The node position is placed using scenePoint which is a projection from the touch location to the scene that was done using SceneKit: unprojectPoint returns same/similar point no matter where you touch screen.

let nodeImg = SCNNode(geometry: SCNSphere(radius: 0.05))
nodeImg.physicsBody? = .static()
nodeImg.geometry?.materials.first?.diffuse.contents = hexColor
nodeImg.geometry?.materials.first?.specular.contents = UIColor.white
nodeImg.position = SCNVector3(scenePoint.x, scenePoint.y, scenePoint.z)
print(nodeImg.position)
            
sceneView.scene.rootNode.addChildNode(nodeImg)

I think this has something to do with the fact that I'm adding the nodeImg node as a child to the rootNode, but I'm not sure what else to anchor it to.

MRR MRR · Accepted Answer · 2021-04-28T10:51:15

On tap you need to set the 'worldPosition' of the node and not just 'position'

Check this link : ARKit: position vs worldposition vs simdposition

Assuming you have set sceneView.allowsCameraControl = false

@objc func handleTapGesture(withGestureRecognizer recognizer: UITapGestureRecognizer) {
    let location: CGPoint = recognizer.location(in: self.sceneView)
    let hits = self.sceneView.hitTest(location, options: nil)
    if let tappednode = hits.first?.node {
        nodeImg.worldPosition = tappednode.worldPosition
        self.sceneView.scene.rootNode.addChildNode(nodeImg)
   }
}

How to limit SCNNode from moving when camera moves along the x-axis?

1 Answers