ARKit: How to place one imported 3D model above another? - ios

Question

I am working on a AR project using ARKit.
If I touch only the imported 3D object on a point, I want to place another 3D object above it.
(For example I have placed a table above which I have to place something else like a flower vase on the touched point).
How can I solve the problem that the second object should only be placed, when I touch the first 3D object?
The surface of the object is not flat, so I can not use hittest with bounding box.

Answer 1

One approach is to give the first imported 3D object a node name.
firstNode.name = “firstObject”
Inside you tapped gesture function you can do a hitTest like this
let tappedNode = self.sceneView.hitTest(location, options: [:])
let node = tappedNode[0].node
if node.name == “firstObject” {
let height = firstNode.boundingBox.max.y -firstNode.boundingBox.min.y
let position2ndNode = SCNVector3Make(firstNode.worldPosition.x, (firstNode.worldPosition.y + height), firstNode.worldPosition.z)
2ndNode.position = position2ndNode
sceneView.scene.rootNode.addChildNode(2ndNode)
} else {
return
}
This way when you tap anywhere else the 2nd object won’t get placed. It will only place when you tap on the node itself. It doesn’t matter where you tap on the node, because we only want the height & we can determine that from its boundingBox max - min which we then add to the firstnode.worldPosition.y
Make sure you set at the top of ARSCNView class
var firstNode = SCNNode!
this way we can access the firstNode in the tap gesture function.
Edit: If the first 3D model has many nodes. You can flattenNode on the parent Node in the sceneGraph (best illustrated with photo below). This removes all the childNodes and wraps from the sceneGraph. You can then just work with the parentNode.