What’s new in ARKit 2

Relocalization from 11.3 allows a session to be restored. Uses a map that is supplied by world tracking.
In iOS 12 you can get a mapping of a physical 3D space
Mutable list of named anchor so you can add your own anchors
Raw feature points and extent
World maps can be serialized (Codable?)
The world map can be loaded again when the user starts their AR experience.

Multi-user experiences

iOS 12 adds support for many users seeing the same world map at the same time
ARWorldMap is shared however you please. For instance air drop or multi peer connectivity.
getCurrentWorldMap is used to obtain the current world map
When you pass a world map to an AR session, it uses the same relocalization that was added in iOS 11.3
More points of view give a better world map
A static well-textured environment gives the best experience
You get a worldMappingStatus that is updated on every frame to tell you how the map is coming along. Goes from Not Available to Limited to Extending to Mapped. If you point to another place, it will go back to limited
There is relocalizing state as well

In 11.3 static, known, images could be detected
Supported by xcode asset catalog
In iOS 12 images don’t need to be static they may move through the world
Orientation and rotation are estimated so you can use images as planes and to trigger the viewing of contents
You can track multiple images
ARImageTrackingConfiguration
ARReferenceImage as a trigger
Feed to ARWorldTrackingConfiguration or ARImageTrackingConfiguration
You can get an ARImageAnchor when an image is found, ARTrackable object
Good images have many features and textures. And good contrast
Xcode will warn you if an image is not likely to be tracked well
Image anchors are represented in the world coordinate system
image tracking configuration is independent from world tracking
position and orientation for every frame