So the GPS waypoint tracking works like a dream. Trouble is, every other part of the system ganged up so I have nothing to prove the perfect performance to you!
First problem was to get Hermione off the ground; every time she took off, either autumn leaves blew around, or the contours of the park caused the Sweep to see an obstacle and land. But I did manage one flight clearing going towards the first waypoint before a leaf called time.
Next problem was the phone attached to the Mavic: somehow it booted into an engineers stats mode (i.e. not Android) meaning it’s much harder to control the Mavic with just the RC, and I could not check the video live.
Then one of the Mavix batteries got too low, meaning a landing and swap.
At that point, I called it a day, at which point my piPod WiFi stopped so I had to risk a hard-poweroff on Hermione.
Everybody is now back home and in working order. Heading back to the park now to rake the autumn leaves away!