How to detect vertical planes in ARKit?

As the iPhone X is featuring a front facing depth camera, my suspicion is that a back facing one will be on the next version and perhaps the .vertical capability will be delegated until then.

Apple has release iOS 11.3 will feature various updates for AR, including ARKit 1.5. In this update ARKit includes the ability for ARKit to recognize and place virtual objects on vertical surfaces like wall and door.

Support for vertical is supported now in ARWorldTrackingConfiguration

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

Support for this is coming with iOS 11.3:

static var vertical: ARWorldTrackingConfiguration.PlaneDetection

The session detects surfaces that are parallel to gravity (regardless of other orientation).

https://developer.apple.com/documentation/arkit/arworldtrackingconfiguration.planedetection https://developer.apple.com/documentation/arkit/arworldtrackingconfiguration.planedetection/2867271-vertical

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.