ARGeoAnchor.AltitudeSource.userDefined
The app defines the altitude.
Declaration
case userDefinedDiscussion
ARKit records this altitude source when your app defines a geo anchor’s altitude.
You may acquire altitude by providing a particular scene coordinate to the session using getGeoLocation(forPoint:completionHandler:).
For example, your app might set a geo anchor’s altitude by raycasting a surface, then adding an arbitrary y-amount to make the anchor more visible from afar.