[jamornh]

If you are able to: 1. Narrow down your GPS coordinate to within the nearest 50 meter radius (really crappy GPS signal.) BUT 2. Are able to use the physical structures surrounding the user to pinpoint the actual precise GPS coordinate. Which Google can do using streetview data.

Then you will be able to triangulate and locate the user quite accurately as long as they are above ground and outside.

And you get this: https://www.youtube.com/watch?v=XWbY5jdJnHg (Interestingly, this just came out today)

With the work that Google is doing for in-door-mapping, this might also work indoors as well as underground, I don't know.

But it seems like the location accuracy for location-based AR is being "solved" right now. Unfortunately, the way it's done can only be done by somebody like Google or a company who can afford to collect streetview level data (maybe Apple can afford to do the same here.)

[Edit] Plus, if you're talking about parallel worlds, Google could even use the Streetview data to potentially pre-render the alternate world over the real world and only send the data back the user after they manage to triangulate them. This way they don't need to do that in real-time, reducing the latency of rendering something over the real world structures.