How to load ARReferenceImage from document directory?

Question

Currently, I am using below code to load ARReferenceImage from "AR Resources" of Assets.xcassets,

guard let trackingImages =  ARReferenceImage.referenceImages(inGroupNamed: "AR Resources", bundle: nil) else {
    print("Missing expected asset catalog resources.")
    return
}
configuration.trackingImages = trackingImages

Now, I am downloading images from the server to the custom folder called "Images" in the document directory of the iOS app.

How can I use those images as "tracking images"?

Answer 1

In order to load custom ARReference images from a specified location other than the default ARAssets Folder you need to create them using the following method:

init(CGImage, orientation: CGImagePropertyOrientation, physicalWidth: CGFloat)

In this example I am using ARWorldTrackingConfiguration but the principle if using ARImageTrackingConfiguration is the same.

Lets say that you store all your downloaded images into an array of [UIImage] e.g:

let imagesFromServer: [UIImage] = [UIImage(named: "gitHubIcon")!, UIImage(named: "stackOverflowIcon")!]

You can then turn these into ARReferenceImages using something like this:

/// Converts An Array Of [UIImage] Into A Set Of ARReferenceImages
///
/// - Parameter images: [UIImage])
/// - Returns: Set<ARReferenceImage>
func loadedImagesFromDirectoryContents(_ images: [UIImage]) -> Set<ARReferenceImage>{

    var index = 0
    var customReferenceSet = Set<ARReferenceImage>()

    images.forEach { (downloadedImage) in

        //1. Convert The UIImage To A CGImage
        guard let cgImage = downloadedImage.cgImage else { return }

        //2. Get The Width Of The Image
        let imageWidth = CGFloat(cgImage.width)

        //3. Create A Custom AR Reference Image With A Unique Name
        let customARReferenceImage = ARReferenceImage(cgImage, orientation: CGImagePropertyOrientation.up, physicalWidth: imageWidth)
        customARReferenceImage.name = "MyCustomARImage\(index)"

        //4. Insert The Reference Image Into Our Set
        customReferenceSet.insert(customARReferenceImage)

        print("ARReference Image == \(customARReferenceImage)")

        index += 1


    }


    //5. Return The Set
    return customReferenceSet

}

Remembering that ARWorldTrackingConfiguration takes a Set<ARReferenceImage>.

You can then initialise your custom configurations detectionImages like so:

 let detectionImages = loadedImagesFromDirectoryContents(imagesFromServer)

 configuration.detectionImages = detectionImages

 augmentedRealitySession.run(configuration, options: [.resetTracking, .removeExistingAnchors])

Hope it points you in the right direction...