ARKit detecting intersection between planes - swift

Question

I am using ARKit (with Scene Kit) and am trying to find a way to get the intersection between an ARReference image and a Horizontal ARPlaneDetection to display a 3D character on the surface directly in front of the detected image, e.g., Spawn inside the red circle see image below
At the moment I am able to get the character to spawn in front of the detected image, however, the character is floating in the air instead of standing on the surface.
let realWorldPositon = SCNVector3Make(anchor.transform.columns.3.x, anchor.transform.columns.3.y, anchor.transform.columns.3.z)
let hitTest = self.sceneView.scene.rootNode.hitTestWithSegment(from: self.sceneView.scene.rootNode.worldPosition, to: realWorldPositon, options: nil)
overlayNode.position = SCNVector3Make((hitTest.first?.worldCoordinates.x)!, 0, (hitTest.first?.worldCoordinates.z)!)
self.sceneView.scene.rootNode.addChildNode(overlayNode)
Any help on this would be greatly appreciated, thanks!
Example project

Answer 1

I think you were on the right lines using the hitTestWithSegment function to detect an intersection between the ARImageAnchor and the ARPlaneAnchor.
Rather than trying to explain each step of my attempt at an answer, I have provided code which is fully commented, so it should be fairly self explanatory.
My example works fairly well (although its certainly not perfect) and will definitely need some tweaking.
For example, you will need to look at determining more accurately the distance from the ARReferenceImage to the ARPlaneAnchor etc.
I can get the model (a Pokemon) to place at the correct level and fairly close to the front of the ARReferenceImage, although it will need tweaking.
Having said this, I think this will be a fairly good base for you to start refining the code and getting more accurate results.
Of note however, is that I have just enabled one ARPlaneAnchor to be detected (just for simplicities sake) and have assumed that you will be detecting a plane infront of your image marker.
I haven't taken into account rotation or anything like that. And of course, based on your proposed scenario; it also assumes your image would be on a desk or some other flat surface.
Anyway, here is my answer (hopefully it should be fairly self explanatory):
import UIKit
import ARKit
//-----------------------
//MARK: ARSCNViewDelegate
//-----------------------
extension ViewController: ARSCNViewDelegate{
func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
//1. If We Have Detected Our ImageTarget Then Create A Plane To Visualize It
if let currentImageAnchor = anchor as? ARImageAnchor {
createReferenceImagePlaneForNode(currentImageAnchor, node: node)
allowTracking = true
}
//2. If We Have Detected A Horizontal Plane Then Create One
if let currentPlaneAnchor = anchor as? ARPlaneAnchor{
if planeNode == nil && !createdModel{ createReferencePlaneForNode(currentPlaneAnchor, node: node) }
}
}
func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {
//1. Check To See Whether An ARPlaneAnchor Has Been Updated
guard let anchor = anchor as? ARPlaneAnchor,
//2. Check It Is Our PlaneNode
let existingPlane = planeNode,
//3. Get The Geometry Of The PlaneNode
let planeGeometry = existingPlane.geometry as? SCNPlane else { return }
//4. Adjust It's Size & Positions
planeGeometry.width = CGFloat(anchor.extent.x)
planeGeometry.height = CGFloat(anchor.extent.z)
planeNode?.position = SCNVector3Make(anchor.center.x, 0.01, anchor.center.z)
}
func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
//1. Detect The Intersection Of The ARPlaneAnchor & ARImageAncho
if allowTracking { detectIntersetionOfImageTarget() }
}
}
//---------------------------------------
//MARK: Model Generation & Identification
//---------------------------------------
extension ViewController {
/// Detects If We Have Intersected A Valid Image Target
func detectIntersetionOfImageTarget(){
//If We Havent Created Our Model Then Check To See If We Have Detected An Existing Plane
if !createdModel{
//a. Perform A HitTest On The Center Of The Screen For AnyExisting Planes
guard let planeHitTest = self.augmentedRealityView.hitTest(screenCenter, types: .existingPlaneUsingExtent).first,
let planeAnchor = planeHitTest.anchor as? ARPlaneAnchor else { return }
//b. Get The Transform Of The ARPlane Anchor
let x = planeAnchor.transform.columns.3.x
let y = planeAnchor.transform.columns.3.y
let z = planeAnchor.transform.columns.3.z
//b. Create The Anchors Vector
let anchorVector = SCNVector3(x,y, z)
//Perform Another HitTest From The ImageAnchor Vector To The Anchors Vector
if let _ = self.augmentedRealityView.scene.rootNode.hitTestWithSegment(from: imageAnchorVector, to: anchorVector, options: nil).first?.node {
//a. If We Havent Created The Model Then Place It As Soon As An Intersection Occures
if createdModel == false{
//b. Load The Model
loadModelAtVector(SCNVector3(imageAnchorVector.x, y, imageAnchorVector.z))
createdModel = true
planeNode?.removeFromParentNode()
}
}
}
}
}
class ViewController: UIViewController {
//1. Reference To Our ImageTarget Bundle
let AR_BUNDLE = "AR Resources"
//2. Vector To Store The Position Of Our Detected Image
var imageAnchorVector: SCNVector3!
//3. Variables To Allow Tracking & To Determine Whether Our Model Has Been Placed
var allowTracking = false
var createdModel = false
//4. Create A Reference To Our ARSCNView In Our Storyboard Which Displays The Camera Feed
#IBOutlet weak var augmentedRealityView: ARSCNView!
//5. Create Our ARWorld Tracking Configuration
let configuration = ARWorldTrackingConfiguration()
//6. Create Our Session
let augmentedRealitySession = ARSession()
//7. ARReference Images
lazy var staticReferenceImages: Set<ARReferenceImage> = {
let images = ARReferenceImage.referenceImages(inGroupNamed: AR_BUNDLE, bundle: nil)
return images!
}()
//8. Scrren Center Reference
var screenCenter: CGPoint!
//9. PlaneNode
var planeNode: SCNNode?
//--------------------
//MARK: View LifeCycle
//--------------------
override func viewDidLoad() {
super.viewDidLoad()
//1. Get Reference To The Center Of The Screen For RayCasting
DispatchQueue.main.async { self.screenCenter = CGPoint(x: self.view.bounds.width/2, y: self.view.bounds.height/2) }
//2. Setup Our ARSession
setupARSessionWithStaticImages()
}
override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() }
//---------------------------------
//MARK: ARImageAnchor Vizualization
//---------------------------------
/// Creates An SCNPlane For Visualizing The Detected ARImageAnchor
///
/// - Parameters:
/// - imageAnchor: ARImageAnchor
/// - node: SCNNode
func createReferenceImagePlaneForNode(_ imageAnchor: ARImageAnchor, node: SCNNode){
//1. Get The Targets Width & Height
let width = imageAnchor.referenceImage.physicalSize.width
let height = imageAnchor.referenceImage.physicalSize.height
//2. Create A Plane Geometry To Cover The ARImageAnchor
let planeNode = SCNNode()
let planeGeometry = SCNPlane(width: width, height: height)
planeGeometry.firstMaterial?.diffuse.contents = UIColor.white
planeNode.opacity = 0.5
planeNode.geometry = planeGeometry
//3. Rotate The PlaneNode To Horizontal
planeNode.eulerAngles.x = -.pi/2
//4. The Node Is Centered In The Anchor (0,0,0)
node.addChildNode(planeNode)
//5. Store The Vector Of The ARImageAnchor
imageAnchorVector = SCNVector3(imageAnchor.transform.columns.3.x, imageAnchor.transform.columns.3.y, imageAnchor.transform.columns.3.z)
let fadeOutAction = SCNAction.fadeOut(duration: 5)
planeNode.runAction(fadeOutAction)
}
//-------------------------
//MARK: Plane Visualization
//-------------------------
/// Creates An SCNPlane For Visualizing The Detected ARAnchor
///
/// - Parameters:
/// - imageAnchor: ARAnchor
/// - node: SCNNode
func createReferencePlaneForNode(_ anchor: ARPlaneAnchor, node: SCNNode){
//1. Get The Anchors Width & Height
let width = CGFloat(anchor.extent.x)
let height = CGFloat(anchor.extent.z)
//2. Create A Plane Geometry To Cover The ARImageAnchor
planeNode = SCNNode()
let planeGeometry = SCNPlane(width: width, height: height)
planeGeometry.firstMaterial?.diffuse.contents = UIColor.white
planeNode?.opacity = 0.5
planeNode?.geometry = planeGeometry
//3. Rotate The PlaneNode To Horizontal
planeNode?.eulerAngles.x = -.pi/2
//4. The Node Is Centered In The Anchor (0,0,0)
node.addChildNode(planeNode!)
}
//-------------------
//MARK: Model Loading
//-------------------
/// Loads Our Model Based On The Resulting Vector Of Our ARAnchor
///
/// - Parameter worldVector: SCNVector3
func loadModelAtVector(_ worldVector: SCNVector3) {
let modelPath = "ARModels.scnassets/Scatterbug.scn"
//1. Get The Reference To Our SCNScene & Get The Model Root Node
guard let model = SCNScene(named: modelPath),
let pokemonModel = model.rootNode.childNode(withName: "RootNode", recursively: false) else { return }
//2.Add It To Our SCNView
augmentedRealityView.scene.rootNode.addChildNode(pokemonModel)
//3. Scale The Scatterbug
pokemonModel.scale = SCNVector3(0.003, 0.003, 0.003)
pokemonModel.position = worldVector
augmentedRealityView.scene.rootNode.addChildNode(pokemonModel)
}
//---------------
//MARK: ARSession
//---------------
/// Sets Up The AR Session With Static Or Dynamic AEImages
func setupARSessionWithStaticImages(){
//1. Set Our Configuration
configuration.detectionImages = staticReferenceImages
configuration.planeDetection = .horizontal
//2. Run The Configuration
augmentedRealitySession.run(configuration, options: [.resetTracking, .removeExistingAnchors])
//3. Set The Session & Delegate
augmentedRealityView?.session = augmentedRealitySession
self.augmentedRealityView?.delegate = self
}
}
Hope it points you in the right direction...