1
You have many options, some of them are - Free tools
Junaio
commercial tools
metaio SDK
ARToolkit SDK for iOS
2
As I understand it, you are requesting the experience of AR based on GPS. Of the above toolkits, Junaio supports this feature.
I think the FLAR toolkit does not support this. It supports brand-based and NFT-based AR http://www.artoolworks.com/products/web/flartoolkit-2/
3
The above toolboxes have good documentation that you can start from there.
4
It clearly depends on your requirements. The FLAR tool is not specifically designed for mobile devices. Therefore, you will have to integrate it into your mobile. The structures I mentioned are specifically designed for mobile phones, including iOS.
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