ARWorldMap

The session state in a world map includes ARKit's awareness of the physical space the user moves the device in (which ARKit uses to determine the device's position and orientation), as well as any ARAnchor objects added to the session (which can represent detected real-world features or virtual content placed by your app).

When your app is quitting, you can save the current world map (acquired using getCurrentWorldMapWithCompletionHandler:). Because ARWorldMap conforms to NSSecureCoding, you serialize it using NSKeyedArchiver.

func writeWorldMap(_ worldMap: ARWorldMap, to url: URL) throws {
    let data = try NSKeyedArchiver.archivedData(withRootObject: worldMap, requiringSecureCoding: true)
    try data.write(to: url)
}

To restore the world map the next time your app launches, use NSKeyedUnarchiver.

func loadWorldMap(from url: URL) throws -> ARWorldMap {
    let mapData = try Data(contentsOf: url)
    guard let worldMap = try NSKeyedUnarchiver.unarchivedObject(ofClass: ARWorldMap.self, from: mapData)
        else { throw ARError(.invalidWorldMap) }
    return worldMap
}

You can use anchors from a resumed world map to place the same virtual content at the same positions from the saved session, if the app is launched in the same physical environment.

For more information, see Saving and Loading World Data.

With two devices tracking the same world map, you can build a networked experience where both users can see and interact with the same virtual content. To send an ARWorldMap to another device, creating a shared frame of reference for multiuser AR experiences:

1. On one device, use NSKeyedArchiver as in to convert the world map to a data object. (You don't need to write the data to a file to send it over the network.)

2. Use the networking technology of your choice to send the resulting data to another device. (For example, in a MultipeerConnectivity session, call sendData:toPeers:withMode:error: to send data, and implement MCSessionDelegate methods on the other device to receive data.)

3. On the receiving device, use NSKeyedUnarchiver as in to instantiate an ARWorldMap from the data.

For more information, see Creating a Multiuser AR Experience.

To begin a new session from an existing ARWorldMap, set a world tracking configuration's initialWorldMap property and use runWithConfiguration:options:. This starts a new session using the same spatial awareness and anchors loaded from the saved world map.