best way to achieve precise persistent AR

What is currently the best way to achieve precise and persistent AR?
I want to precisely place an AR objects in a very specific outdoor environment that I can map in advance.
I have been looking at Placenote and ARKit's ARWorldMap as a way to map the environment, embed it in my app and allow a user to "snap" to this environment to acquire the correct position.
This seems more precise than GPS based approaches including the 'AR + GPS Location package'.

- Is this correct? Is mapping a place and then allowing the user to snap to this existing map the best approach for precise placement of AR markers in a defined space (such as a park)

- Is there a maximum / preferred dimension of a map? Can you map a 100m x 100m park in a way that a user can snap to it?

- Is there a difference between using Placenote or ARKit's ARWorldmap, or in the first based on the latter?

- Are there better alternatives / frameworks?

 

arworldmap is the only solution that exists right now, unless you roll your own.

 

There is a plutora of startups that serve a precise persited AR cloud.
Here's just a few not mentioned allready in this thread:

https://youar.io/
https://www.spatialcanvas.com/
https://www.jidomaps.com/
https://www.6d.ai/

They all seem to offer and promise more or less the same.

 

@sdnAu2mate Thank you for the list. It is very helpful with finding better alternatives.