How to Detect Vertical Planes in Arkit

Using both horizontal and vertical planes in ARKit / RealityKit

ARKit 5.0

You can do it as usually, using the habitual approach:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    let configuration = ARWorldTrackingConfiguration()
    configuration.planeDetection = [.horizontal, .vertical]
    arView.session.run(configuration)
}

planeDetection instance property is gettable and settable:

var planeDetection: ARWorldTrackingConfiguration.PlaneDetection { get set }

...and PlaneDetection struct conforms to OptionSet protocol which allows you to use just a single value or both values at the same time:

configuration.planeDetection = []
configuration.planeDetection = .vertical
configuration.planeDetection = [.horizontal, .vertical]

Then add renderer(_:didAdd:for:) instance method to your code that might look like this:

func renderer(_ renderer: SCNSceneRenderer,
             didAdd node: SCNNode,
              for anchor: ARAnchor) {
    
    guard let planeAnchor = anchor as? ARPlaneAnchor 
    else { return }

    let width = CGFloat(planeAnchor.extent.x)
    let height = CGFloat(planeAnchor.extent.z)
    let myPlane = SCNPlane(width: width, height: height)           
    
    if planeAnchor.alignment == .horizontal {
        myPlane.materials.first?.diffuse.contents = UIColor.semiOpaqueRed
    } else if planeAnchor.alignment == .vertical {
        myPlane.materials.first?.diffuse.contents = UIColor.semiOpaqueCyan
    }
    
    let planeNode = SCNNode(geometry: myPlane)
    let x = CGFloat(planeAnchor.center.x)
    let y = CGFloat(planeAnchor.center.y)
    let z = CGFloat(planeAnchor.center.z)
    
    planeNode.position = SCNVector3(x, y, z)
    planeNode.eulerAngles.x = -.pi / 2
    
    node.addChildNode(planeNode)
}

And, at last, add renderer(_:didUpdate:for:) instance method that might look like this:

func renderer(_ renderer: SCNSceneRenderer,
          didUpdate node: SCNNode,
              for anchor: ARAnchor) {
    
    guard let planeAnchor = anchor as? ARPlaneAnchor,
          let planeNode = node.childNodes.first,
          let myPlane = planeNode.geometry as? SCNPlane
    else { return }
    
    let width = CGFloat(planeAnchor.extent.x)
    let height = CGFloat(planeAnchor.extent.z)
    myPlane.width = width
    myPlane.height = height
    
    let x = CGFloat(planeAnchor.center.x)
    let y = CGFloat(planeAnchor.center.y)
    let z = CGFloat(planeAnchor.center.z)
    planeNode.position = SCNVector3(x, y, z)
}

RealityKit 2.0

It only takes a few lines of code to implement this idea in RealityKit.

let arView = ARView(frame: .zero)
let model = try! ModelEntity.load(named: "Model.usdz")

let anchor = AnchorEntity(plane: [.horizontal, .vertical], 
                 classification: [.floor, .wall], 
                  minimumBounds: [0.5, 0.5])

anchor.addChild(model)
arView.scene.anchors.append(anchor)

How to detect vertical planes in ARKit?

Edit: This is now supported as of ARKit 1.5 (iOS 11.3). Simply use .vertical. I have kept the previous post below for historical purposes.

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TL;DR

Vertical plane detection is not (yet) a feature that exists in ARKit. The .horizontal suggests that this feature could be being worked on and might be added in the future. If it was just a Boolean value, this would suggest that it is final.

Confirmation

This suspicion was confirmed by a conversation that I had with an Apple engineer at WWDC17.

Explanation

You could argue that creating an implementation for this would be difficult as there are infinitely many more orientations for a vertical plane rather than a horizontal one, but as rodamn said, this is probably not the case.

From rodamn’s comment:
At its simplest, a plane is defined to be three coplanar points. You have a surface candidate once there are sufficient detected coplanar features detected along a surface (vertical, horizontal, or at any arbitrary angle). It's just that the normal for horizontals will be along the up/down axis, while vertical's normals will be parallel to the ground plane. The challenge is that unadorned drywall tends to generate few visual features, and plain walls may often go undetected. I strongly suspect that this is why the .vertical feature is not yet released.

However, there is a counter argument to this. See comments from rickster for more information.

ARFoundation detecting vertical planes and placing objects - Unity

ARFoundation 1.0.0 preview 22 will surface the ability to select your plane detection mode: horizontal, vertical, or both. To use this mode, you will have to upgrade to the newly released Unity 2018.3: https://blogs.unity3d.com/2018/12/13/introducing-unity-2018-3/

For more about plane detection in ARFoundation, refer the following link

AR Plane Manager

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