You need to use your judgement, and possibly the OS map…
Or google maps if you can’t be arsed flapping about with all that
Thank you for your advice. I suppose at the end of the day we all use our judgement on many flights. Watching the lay of the land, etc etc etc. Thank you for the advice
Thank you for the advice on this matter. I suppose at the end of the day it’s a judgement call.
1 Like
No, because you need the contour values (not just some pretty pictorial shading) to caclulate your height away from ground/agl at a given position. If you’ve flown out horizontally from directly above the summit of a 500m asl mountain at 50m agl/Home Point and you know you are 30maway on bearing x, you need to know the height asl of the ground beneath your drone at that point. A ground height estimated from the contour, which is given in metres on the OS map, of, say 410m asl, means that the ground at that point is 90m lower than the Home Point (summit), + 50m above Home Point means you are 140m above the ground. You need to lose 20m of your altitude to be within the 120m rule, so you are looking for a height on the screen of 100m or less. As you fly further away from Home Point you will need to fly at lower altitudes, possibly even in minus values as measured from Home Point. Google Maps, which do not show contour lines, are useless for this purpose!
3 Likes
Thank you guys for your concise advice. Fascinating. So now all I got to do is get the bloody thing up in the air. 
1 Like
I’m sure similar conversations are happening/have happened throughout 120m-land. What are the chances of DJI fixing it? I’d imagine it’s just a change coding that is required, no hardware change. While it’s a real buggers’ muddle it’s also very interesting (at least to this newbie).
Perhaps, using your GPS location as the trigger, the 120m above take off is for the european rules
Daft that my much heavier UK1 drone has no such limit
1 Like
Interesting, useful to know, and I’m duly ejermakulated. But, given that I would only have the one (iPhone) screen available in most flying situations, I still think a paper OS map is probably the simplest solution. In actual practice, the only time I’ve done this was off the top of Caerphilly Mountain at fairly close range and I’m reasonably certain that I was happily within the 400’/120m of the ground in that case just by line of sight and judgement (it was on this flight, and a later one off Penarth Head, that I learned that the screen will show height in minus figures relative to Home Point). It’s a potential issue on bigger mountains with steeper slopes, though; even without gaining any extra height, you wouldn’t go very far horizontally off the summit of Yr Wyddfa, or Cadair Idris, or Ben Nevis, before you were heading into illegal airspace. In such a case, it is probably best to keep within 400’/120m horizontal range of the Home Point, so that you know you are (whatever DJI’s screen says about your height) within those distances from the nearest point on the surface of the planet, which is what the CAA want!
How many maps do I need , I’ve flown all around the UK,Europe and further afield with no issues planning on Google maps.
Check before flight unless you’re telling me you’re checking the paper map as you’re flying ?
Pretty sensible seen as real planes use the 500ft + airspace , you did know that right ?
Hi, yes I expect my is working on it or it’s been already done and they haven’t told us about it. Which I understand they do that. Quite a lot. I suppose the only way is to find out is to shoot it up to 400 ft and see what happens. I have been reading stuff that DJI do update and don’t really tell anybody what they have done to improve reliability or the boundaries of the drone. So it’s highly likely that they have done something tweaked it I do not know.
.
They haven’t
Oh well, what a pity. Wouldn’t it be nice if they do that before Christmas as a present. Chances were you’re fine thing I know. Miracles do happen in the drone world I suppose. Or just woke up. I was dreaming that we were a flying amount of no restrictions. But I made myself a coffee. Get myself back to reality.