The RTK GPS by Emlind, is currently out of stock on their website. And its also quite expensive. We are looking at around £575.
So, at this time using GPS to get inch perfect location is not viable.
Maybe in 3 years when the device is cheaper and lighter it will be an option.
1, One method could be to position a cheap camera under the drone.
2, When saving home location, we take pictures of the home location.
3, Using GPS, we bring the copter into approximate position.
4, Then we use the camera, to take pictures and compare those pictures with the pictures taken in Step 2 and attempt to match up. As soon as we have a match, we announce "arrived home".
I know that Amazon use a visual system like this with their drones, where the drone attempt to search for a visual landmark.
Another method would be to use a lidarlite, on a horizontal, mode, spinning around, measuring horizontal distances to vertical objects around it. Providing the copter has the correct heading, this should allow the copter to use vertical objects around it, to estimate its position. This method would not work on a plain, eg a desert where there are no vertical objects.
I need to make some refinements to the FOLLOW ME mode. After this is done, I will be putting up a video soon, where the copter shall mimic the behaviour of a dog.