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Question On Altitude When Flying From A Hilltop

Ah so the drone does not "adjust" to actual AGL then .... I thought it would show 10' in (my scenario above - post 17) then as we fly straight out (horizontally at the same height) over the valley it would show increasing height in its reading.
No it would just show 10' until you go up or down relative to your take off point, so yes you CAN go down and go into minus height.
 
Ok so how do you know (based on the app) at what height you're really flying at (AGL) if you're flying in hilly country? For instance lets say you're at the top of a 500' hill (your home point) and you take off, climb to 10' and then fly straight out horizontally from that height. Now according to the app you're flying at 10', whereas you're actually flying at 510' AGL! (which now makes you illegal) So, in a case like this (hilly country flying) how would you even know when/if you're flying legally or not ... since you're going by the apps feedback in your flight?
right i fly a great deal in not just hilly, but mountainous terrain in my part of the world,and if it is somewhere new that i have not flown before, then i use a ordnance map with height above sea level displayed on the map, so i am able to see where i am and then look where i am going to fly, and i know what the height of the lowest point is in relation to my home point if as an example my take off height is 600 ft ASL and the valley floor is 300 ft ASL then i know that i can go up from my take off home point say 50 ft then if i do not fly higher than that during the flight i will always be in the 400 ft AGL zone,if the difference between the take off point and lowest point is greater than 400 ft then i would descend to a negative figure on the app and i would always be compliant, in reality there are always going to be times when you do not comply exactly with the 400 ft rule but that would only have a bearing if you were involved in litigation due to crashing into something or someone,just use common sense
 
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No it would just show 10' until you go up or down relative to your take off point, so yes you CAN go down and go into minus height.
Yeah that’s too bad cause like I mentioned before you really can’t know your “true AGL” in hilly country. You can’t even do the math cause you wont know your home point height relative to the changing landscape (valleys etc) that you’re flying over.
 
I’m trying to figure out why you say that. . It’s the same thing you just said. I got that from here seeing it posted hundreds of times with this same question and never have I seen that
posted about it .
Im just curious what’s not quite right about it.

It's the official UK CAA interpretation of the 400 ft rule - 400 ft from the nearest ground rather than the US FAA interpretation of 400 ft above the ground directly below the aircraft.
 
10' may be a bad example as Go will show you AGL from the VPS sensor when that close to the ground. Another 5 to 10ft and the VPS altitude is not available. At that point AC can't determine ground height below any more than a manned aircraft can. It's all done by barometer relative to barometer calibration setting.
 
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just to clarify what i said in my post#12 the bit where i said you could fly up to the top of a 600 ft hill and still be in compliance , i should have mentioned that in order to achieve that one of two things need to be done
(1) increase the max height setting to allow the drone to fly higher than 400 ft
(2) as you ascend climb up the hill 200 ft or so, so that the 120m setting for max height would allow you to reach the top
if you just flew up from the home point the drone would geofence once it reached 120m and you would not get to the top
 
Ah so the drone does not "adjust" to actual AGL then .... I thought it would show 10' in (my scenario above - post 17) then as we fly straight out (horizontally at the same height) over the valley it would show increasing height in its reading.
no it only knows it height above the home point
 
It's the official UK CAA interpretation of the 400 ft rule - 400 ft from the nearest ground rather than the US FAA interpretation of 400 ft above the ground directly below the aircraft.
Thanks, I snatch the wrong diagram. Whoops
 
I have mountain property that ranges from 10,000' to 12,400' that I really need to fly over for several reasons. Flying it continuously uphill is completely impossible as the AC collision avoidance system will kick in to avoid colliding with the ground, in some cases within 200' horizontal distance.
The alternative in this case is climbing to each point at the next 400' elevation gain above sea level and flying the next 400' ascent. 400' AGL provides the field of view I need, so climbing to the top of the property and flying downhill is about the only option. Maintaining anything close to 400' AGL would be conjecture at best. Visually estimating altitude above ground line from a point above is nearly impossible from a technical standpoint. Calculating altitude based on aircraft position and contour lines on a map corresponding to the app location on my tablet screen would consume most of the limited flight time available from each battery.
I could just wing it, try to stay within the 400' limit, but it's much easier to comply with regulations than to defend your rationalization why you didn't comply, so the enigma is wrapped in a conundrum wrapped in a flour tortilla. In some areas I can literally gain 800' altitude by moving 25'.
If I want to publish the video or photos from my reconnaissance of this historic area (which was my original plan) and do it without fear of being found in violation, it will take literally months rather than a single day. Comply or violate? There really isn't a choice, it's compliance.
I have tried to source a number of distance detector/ ranging devices that would be appropriate for UAVs similar to the MA. Weight is a factor- sensors that can measure to 330' weigh about 4 ounces or more. I've found dopler sensors that weigh in at just over an ounce, but transmitting the data and integrating it into the DJI app or developing another app is a challenge and adds significant weight. In addition, the distance with the smallest doppler units in a size suitable for a UAV is limited to less than 100 feet.
While a lot of us would love to have the AC maintain 400' AGL over contours, I doubt it is an adequate market size to justify development of a light weight add on. But who knows, there a lot of talented and creative people out there.
 
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I have mountain property that ranges from 10,000' to 12,400' that I really need to fly over for several reasons. Flying it continuously uphill is completely impossible as the AC collision avoidance system will kick in to avoid colliding with the ground, in some cases within 200' horizontal distance.
The alternative in this case is climbing to each point at the next 400' elevation gain above sea level and flying the next 400' ascent. 400' AGL provides the field of view I need, so climbing to the top of the property and flying downhill is about the only option. Maintaining anything close to 400' AGL would be conjecture at best. Visually estimating altitude above ground line from a point above is nearly impossible from a technical standpoint. Calculating altitude based on aircraft position and contour lines on a map corresponding to the app location on my tablet screen would consume most of the limited flight time available from each battery.
I could just wing it, try to stay within the 400' limit, but it's much easier to comply with regulations than to defend your rationalization why you didn't comply, so the enigma is wrapped in a conundrum wrapped in a flour tortilla. In some areas I can literally gain 800' altitude by moving 25'.
If I want to publish the video or photos from my reconnaissance of this historic area (which was my original plan) and do it without fear of being found in violation, it will take literally months rather than a single day. Comply or violate? There really isn't a choice, it's compliance.
I have tried to source a number of distance detector/ ranging devices that would be appropriate for UAVs similar to the MA. Weight is a factor- sensors that can measure to 330' weigh about 4 ounces or more. I've found dopler sensors that weigh in at just over an ounce, but transmitting the data and integrating it into the DJI app or developing another app is a challenge and adds significant weight. In addition, the distance with the smallest doppler units in a size suitable for a UAV is limited to less than 100 feet.
While a lot of us would love to have the AC maintain 400' AGL over contours, I doubt it is an adequate market size to justify development of a light weight add on. But who knows, there a lot of talented and creative people out there.

You are overthinking this problem. You can set the maximum height to 500 meters and get most of that terrain while staying within 400 ft of the ground. Yes - you will be eyeballing it much of the time, but you are not going to be far off. The bigger issue by far is maintaining VLOS over those kinds of distances and height excursions.

Or you can create a Litchi mission in AGL mode.
 
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You are overthinking this problem. You can set the maximum height to 500 meters and get most of that terrain while staying within 400 ft of the ground. Yes - you will be eyeballing it much of the time, but you are not going to be far off. The bigger issue by far is maintaining VLOS over those kinds of distances and height excursions.

Or you can create a Litchi mission in AGL mode.
Okay, makes sense. How do I set the max height to 500 meters? I looked at it when I first got my MA and couldn't set it for anything above 400' (121 meters). Haven't tried to revisit the matter since it seemed easier to overthink it.
 
Okay, makes sense. How do I set the max height to 500 meters? I looked at it when I first got my MA and couldn't set it for anything above 400' (121 meters). Haven't tried to revisit the matter since it seemed easier to overthink it.

The setting in the app goes up to 500 m.
 
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Okay, makes sense. How do I set the max height to 500 meters? I looked at it when I first got my MA and couldn't set it for anything above 400' (121 meters). Haven't tried to revisit the matter since it seemed easier to overthink it.
You must have the drone turned on to see the settings to change on your controlling device.
 
You must have the drone turned on to see the settings to change on your controlling device.
Thank you, I'll do that at my next opportunity. I fly a lot of canyons in addition to mountains so it will definitely broaden my horizons. I tend to rely on built in fail safes when it comes to compliance issues.
 
There are two, very specific, measures of height for "aviators".

The first is Above Mean Sea Level, (AMSL). This is a measure based upon the pressure at sea level which is considered pretty much a fixed altitude compared to the pressure at the altitude you are at. The difference in pressure gives you a reasonable estimation of your height above the ocean and is a fixed and unarguable altitude.

The second is Above Ground Level, (AGL). This is the important one for droners but it is also more complicated in practice because the "G" in AGL isn't a relative constant like the pressure is in the AMSL calculation of altitude.

If you look out in your back yard most people will have a slope on it. Let's say the ground in your yard slopes east to west downwards by one foot over a 50 foot yard. If you are assessing altitude using the AMSL system and place a drone at 400' AMSL over your yard at the high side and then move it 50 feet west it will remain at 400' AMSL but that same movement will have altered its AGL by one additional foot - so now you are at 401' and are exceeding the allowable flight envelope. Tut, tut, :)

The problem with AGL is that the "G" varies so much all around you that it gets a bit complicated because the drone isn't helping you. The drone's system is using the home point as, effectively, sea level and then tells you how high it is above or below that. So if you stand at the very top of El Capitan and start up your drone you will start at 0'. Fly it out 100' and the altitude it reports around 3000' because, (IIRC), that is about what El Capitan is from top to bottom almost vertically. But it's AMSL altitude didn't change an inch.

In order to have a precise measure of AGL the drone either needs to have an accurate and functional Radar Altimeter, (RadAlt), or have a great GPS with good - direct - internet connection that gives accurate topographical information in order for it to assess it's AGL...

As a rule the altitude of your aircraft in terms of AMSL and AGL does not change as you move it laterally over water and some very extraordinary places in the world. Other than that, as you move off any particular coordinate in the world the AMSL will remain fairly constant but the AGL will be wildly different in both positive and negative coordinates.

I hope that all makes some sense...
 
Everything I've learned is 400' AGL simply means straight down below the aircraft with no reference to slope. So there is no horizontal measurement at all. That makes flying off the top of a cliff that has a vertical drop of more than 400' practically impossible to do legally as a rec flier in the USA. There was another thread a few weeks back that was incorrect as far as the FAA regulation. BUT I do think we should have a horizontal limit similar to how the UK has.
 
Everything I've learned is 400' AGL simply means straight down below the aircraft with no reference to slope. So there is no horizontal measurement at all. That makes flying off the top of a cliff that has a vertical drop of more than 400' practically impossible to do legally as a rec flier in the USA. There was another thread a few weeks back that was incorrect as far as the FAA regulation. BUT I do think we should have a horizontal limit similar to how the UK has.

That's correct. In the US the diagram would look like this:

400ft_rule.jpg
 
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Everything I've learned is 400' AGL simply means straight down below the aircraft with no reference to slope. So there is no horizontal measurement at all. That makes flying off the top of a cliff that has a vertical drop of more than 400' practically impossible to do legally as a rec flier in the USA. There was another thread a few weeks back that was incorrect as far as the FAA regulation. BUT I do think we should have a horizontal limit similar to how the UK has.
That's why I say as a practical standpoint, you can't be faulted for being above 400ft off a cliff if you're right beside the cliff, say within 100' of the face, and descending. A contradictory plane/chopper would be more in danger with the cliff than with you.
 
It doesn't use GPS for height, except in the EXIF data. It uses barometric pressure.

Ah good to know, the EXIF data is what led me to believe it was all GPS based. Barometer in the MAVIC makes more sense.
 
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