Augmented reality, enforced locality, geometric hashing

I had discussion with Lester Madden at linkedin MAR group. The thing we discussed was the concept of the locality in the AR. That is, each AR object should be attached to specific location and accessible only from that location.
I’ll try explain it more in depth here.
Augmented graffiti, augmented reality mail/drop boxes and billboards, user-built reality overlays – all of those should be attached to specific location. This locality could be enforced – only local data would be available (filtered into) in the specific location. This locality of data prevent user from sinking in the augmented noise, generated all other the world, and reduce possibility of spam.
For example you can have neighborhood billboard, leave note for the friends in the park and so on. All those AR objects data could be accessed only locally for both read and write – to read billboard and to post a message on it you would have to go to it.
The user should get the data/content only if he is physically present at the specific location. The same way poster/producer of the data or AR object should physically visit each location where it placed.
If locality is enforced, to place note for your friend in the park you have to visit park, and there is no way around it.
Locality could be enforced with location-based encryption. I think this encryption could be made with use of geometric hashing. User scan environment and make 3d registration with his mobile or wearable device. Encryption key is generated by mobile device from the scanned 3d model of the environment.
If user want to get data attached to the location, he access the server, retrieve local data and decrypt them with that key.
In the opposite direction, if user want to attach some object or data to location, mobile device encrypt data with part of the hash key and send other part of the key to server. Before storing data the server do uniqueness check. Nearby data already stored on the server are checked, and the new data allowed in only if there is some distance from new key to keys of all the other stored data. After that new data encrypted with the second part of the key by server and stored.
Each object encrypted by two keys, one of which is server side. Server have no access to content of the data, but have access to the part of the location hash key. That way no two objects or data attached to exactly the same location. Clattering of AR objects could be reduced. More importantly if poster have to physically visit location where he want to place AR object, he should have at least some relation to that location, and he is not some spammer from the other end of the world.
If spammer forge location key without actually visiting the place, that will most probably be non-existing location, and no one will be hit by his data.
That all is of cause is a rough outline of how could enforced locality works. Building robust algorithm for extracting geometric hash could be non-trivial.