Testing drone functions, nearly browning the trousers. Technical version. 240513

Flying any DJI drone from a moving object like a car, a boat or as I did, from a train means making a one way trip. The DJI safety system is based on a return ticket flight giving only half the distance before the RTH, Return To Home, function kicks in as the system reserves battery power for a return flight.
A trick, shown by other YT drone flying people was tested. The home point was changed to a new location. Then pressing the RTH button the start was frightening....
Time 01:00. Seagulls....
Time 01:10. What the .......? Okey, keeping the altitude and flying.....
Time 01:11. The yellow H symbol gets wings, in a good direction.
Time 01:13. Going for the river as well. Hey there....
Time 01:20. Left the river, back above ground.
Time 01:42. Seeing the operation would end as expected, RTH was aborted for some train hunting.
Not much was spotted. End the flight using RTH from distance. See how that turned out.
Thanks for watching and reading.

[@thomasmaughan4798]

The Home point symbol is calculated from where the drone knows it is, and a *compass direction* from the drone. It also assumes the existence of a plane field and does a bit of trigonometry to decide where to put the H in the image.
IF there's a significant difference in the H and where you expect it to be, it is likely the compass is out of calibration at that location; unsurprising given the amount of metal likely embedded in the concrete. Once it got out over the water away from all that metal it recalculated the direction to fly.
If the compass remained out of calibration you will almost certainly get a "fly away" drone trying to reach home but it has the wrong direction to fly to get there. That's when you cancel RTH and just fly it manually.
I almost never use RTH, did so for the first time a couple of days ago and was surprised that it came in on a slope rather than straight down. This could be bad in a crowded environment; trees or building.

[@Stefan_Boerjesson]

I carried the not powered drone out to its take off point. Took off and waited for it to established the Home Point.
Then, on the control, executed "Update H P to controller position" which was confirmed. After that RTH was pressed just for checking the system up.
Compass calibration was needed December 2 2023 the last time.
The odd thing, as I find it, is the odd positioning of the yellow H out in the water, and first heading for it.
Now and then I see the H being seriously wrong, at distance, but managing later, at closer distance.
No, RTH is an emergency functioin not used, only the H now and then. Look at the going home, landing, in the video "Fourth attempt......".
Thanks for Your long message, and watching.