One of the recent added capabilities of ATAK is Rubber Sheeting. Rubber Sheeting allows a user to take a photo of a map, import it into ATAK and georectify it. Then, once rectified, it can be converted into a KMZ and treated as a GRG, That means that you can change the transparancy or turn it off or on as well.
The Rubber Sheet tool is the fastest and most accurate of any tool I’ve tried in Android, and in most cases, its actually better than similar desktop tools that do georectification.
Here’s video demonstration