ARKit 1.5 backward compatibility with devices that don't have 11.3

I'm successfully building and using ARKit 1.5 apps with the ARKit unity plugin spring 2018 update branch on a device that I've updated to the iOS 11.3 beta. On a device with 11.2, though, the ARKit scene crashes on load.

How can I make the app backward compatible so iOS 11.2 devices can still use ARKit with the horizontal planes and 11.3 devices can use the vertical planes?

 

Don't have a callstack but I was able to find a workaround for what I needed.

Since I am only interested in vertical planes (and not Image Targets or other ARKit 1.5 features), I was able to fix the issue by modifying the ARSessionNative.mm file. I commented out all the ImageTarget related methods and put in a runtime conditional to check for iOS 11.3. Seems to work fine on my initial tests, I was able to use vertical planes on an 11.3 device but the app still ran fine on an 11.2 device using only horizontal planes.

 

I'm using the 2D image detection, and it's working great:

but I'm having similar issues trying to maintain compatibility with pre iOS 11.3 devices. In Xcode if I change the deployment target to < 11.3 (e.g. 11.0) I get an Asset Catalog Compiler Error:

..../Xcode/Unity-iPhone/Images.xcassets: Exception while running actool: *** -[__NSDictionaryM setObject:forKey:]: object cannot be nil (key: catalog)

Looks like this has been logged as a bug with Apple, but I thought I'd mention it here in case anyone else runs into the same issue:

https://forums.developer.apple.com/thread/96235

 

Hi Jimmy - I just tried it then and get the same error

 

I also get the error running the sample image detection code, so I don't think it is a Unity issue: https://developer.apple.com/documentation/arkit/recognizing_images_in_an_ar_experience