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POLL: On Altitude Readings
2292 26 2017-5-29
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KevDrones
Second Officer
Flight distance : 475522 ft
United States
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Who would like to have DJI change the alltude readings to the real altidude rather than the negative numbers or the lower altidude that it is?
Single SelectVote, Total 81 people participate in voting

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35.80% (29)
27.16% (22)
17.28% (14)
8.64% (7)
11.11% (9)
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2017-5-29
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Bradders
Second Officer
Flight distance : 862283 ft
United Kingdom
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In the UK there is a max flight altitude of 400FT, is this 400FT above sea level or above take off point ?, I ask this because what if you took off from a hill ?
2017-5-29
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Panaceabeachbum
lvl.3
Flight distance : 871430 ft
United States
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I would like the altitude numbers to be an accurate reading above the terrain directly bellow the quad
2017-5-29
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Panaceabeachbum
lvl.3
Flight distance : 871430 ft
United States
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Didnt answer poll because I dont really understand the question your asking, "real " altitude relative to what, sea level?
2017-5-29
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hallmark007
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Bradders Posted at 2017-5-29 06:33
In the UK there is a max flight altitude of 400FT, is this 400FT above sea level or above take off point ?, I ask this because what if you took off from a hill ?

Max altitude is AGL, Not take off point but once whatever ground is underneath the Mavic measures 400ft AGL you are within your guidelines.
2017-5-29
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patman89
Second Officer
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Germany
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Would be great if you can decide which setting you prefer. AGL or ASL.
2017-5-29
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Michael Kaine
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Panaceabeachbum Posted at 2017-5-29 06:47
I would like the altitude numbers to be an accurate reading above the terrain directly bellow the quad

I will second this.
I flew very low through a Forrest and up a stream a few days ago an my altitude was between -32ft and -26ft the entire flight
2017-5-29
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Xman1
Second Officer

United States
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AGL is the important number as this is what the rules are based on.  ASL would be nice to know just to know it, but if you are trying to follow the rules, then AGL is what matters.
2017-5-29
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CAAirborne
Second Officer
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United States
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I would like to see both the altitude above mean sea level as well as altitude above ground level from the home point.  Knowing the absolute altitude helps plan/execute flights where the ground surface elevation changes (i.e., a sloping terrain).
2017-5-29
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Levurmion
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Indonesia
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I think the reason why they haven't done this so far is due to the limitations of the optical and ultrasonic sensors. The ultrasonic sensors are reliable only up to 5m height from any solid surface while the optical sensors to 10m. Higher than that, only the barometer can provide altitude readings as air pressure is the only constant variable left that can be reliably measured.

For instance, when flying horizontal at 20m altitude away from the take off point, neither the ultrasonic nor optical sensors can detect the ground below it hence the aircraft is oblivious to the changes in ground elevation. However, despite the changes in ground elevation, air pressure remains constant with the air pressure at 20m above the take off point. Thus, the drone still reads 20m.

Commercial aircrafts use sonars with much farther effective range as they use radio waves. However, given the importance of the connection between the RC and the aircraft, DJI must have been unwilling to compromise the quality of the connection just to allow the aircraft to have live ground altitude readings. Sonar waves might interfere with the RC signal.
2017-5-29
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rydfree41
Second Officer
Flight distance : 153268 ft
United States
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A laser range finder , that's what the Mavic needs . Yep , a laser
2017-6-2
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Panaceabeachbum
lvl.3
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rydfree41 Posted at 2017-6-2 05:00
A laser range finder , that's what the Mavic needs . Yep , a laser

I believe you mean a frkn lazer
2017-6-2
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rnrnrn
Second Officer
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Germany
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Michael Kaine Posted at 2017-5-29 07:30
I will second this.
I flew very low through a Forrest and up a stream a few days ago an my altitude was between -32ft and -26ft the entire flight

This happens very often. GPS is relatively reliable (nowadays) for a position fix but not for your altitude. Second thing - if you take off quickly the position and it's height will be recorded but given the accuracy you will later get a better value - the problem being that the first value was quite a bit off hence you can get a false reading later on.
2017-6-2
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fans79a9d393
lvl.2
United States
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Ideally one could see both AGL & ASL readings but this would be pretty difficult to have real time continual AGL that is accurate.
It would require highly accurate terrain / topo maps coupled with GPS location or highly accurate rangefinder with minimum 400 foot range.

On somewhat related topic. DJI, could you PLEASE make it so if I choose "Imperial" units of measurement that it then shows RTH altitude as FEET instead of METERS.
That shouldn't be that difficult a technical challenge!  
2017-6-2
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WolfgangStiller
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United States
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I am not sure what the survey is about. Yes, I'd like a more accurate altitude but what are we voting on here?
2017-6-2
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MTUFLYER28
Second Officer
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United States
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I'd at least like the option to read true pressure altitude, gps alt, agl reading based on takeoff location, and or your occustic/optical range finder value for low alt. Work.  All this information is available and being used so it would just require some minor software tweaks to let you display it.
2017-6-2
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Bill in Ohio
Second Officer
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Bradders Posted at 2017-5-29 06:33
In the UK there is a max flight altitude of 400FT, is this 400FT above sea level or above take off point ?, I ask this because what if you took off from a hill ?

I would assume that they mean AGL (not necessarily your takeoff point, but the terrain beneath the aircraft/drone).  The restriction in the US is 400 feet AGL not MSL (Above Ground Level vs Mean Sea Level.  So if the terrain climbs and you are flying level, your altitude in MSL would stay the same, but AGL would decrease, so yes you can climb to keep your clearance.  When I flew F-4s our minimum altitude was always in AGL.  In Germany that was 1000', in Turkey where we were flyinig it was not below your comfort level (about 50 - 100 ft.), Low level route minimum altitudes in the US vary by where you are located.
2017-6-6
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Bill in Ohio
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Levurmion Posted at 2017-5-29 09:02
I think the reason why they haven't done this so far is due to the limitations of the optical and ultrasonic sensors. The ultrasonic sensors are reliable only up to 5m height from any solid surface while the optical sensors to 10m. Higher than that, only the barometer can provide altitude readings as air pressure is the only constant variable left that can be reliably measured.

For instance, when flying horizontal at 20m altitude away from the take off point, neither the ultrasonic nor optical sensors can detect the ground below it hence the aircraft is oblivious to the changes in ground elevation. However, despite the changes in ground elevation, air pressure remains constant with the air pressure at 20m above the take off point. Thus, the drone still reads 20m.

Air pressure is not constant.  When operating in lower altitudes, you set the altimeter to the airports barometer setting.  At higher altitudes you use 29.97.  Airport settings can vary significantly over a short distance due to the effects of High and Low pressure areas a a front moves through.  A cause of accidents on approaches to land is when the pilot forgets to change his altimeter from 29.97 to the local airport setting resulting in being to low and running into the ground.
2017-6-6
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MikeQView
Second Officer
United Kingdom
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  For a Drone , there is no other requirement than AGL, ( in feet would be a bonus)   maybe, "a nice to have" Above MSL, especially if you fly up in the mountains,   but to get that information acurately and reliably is somewhat difficult as already explained here.  my guess is its not worth the effort,  best if the pilot makes him/her self aware of the flight route and changes in elevation,  and then calc this from your take off position,    a quick check on google earth ( altitude of ground level)  of your proposed flight route,  and there you have it.  even though the mavic has a lot of computing power, adding more for it to do, will just add to the complexity.
2017-6-6
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WolfgangStiller
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Could  you please rephrase the poll question? It's still not clear what is meant by "real altitude" so there's no telling what people think they are voting on.
2017-6-6
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Levurmion
lvl.2
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Indonesia
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Bill in Ohio Posted at 2017-6-6 05:20
Air pressure is not constant.  When operating in lower altitudes, you set the altimeter to the airports barometer setting.  At higher altitudes you use 29.97.  Airport settings can vary significantly over a short distance due to the effects of High and Low pressure areas a a front moves through.  A cause of accidents on approaches to land is when the pilot forgets to change his altimeter from 29.97 to the local airport setting resulting in being to low and running into the ground.

Of course, my mistake. I mean almost constant. There are obviously factors that contribute to these fluctuations but for the sake of making things simple, I assumed that generally, air pressure is inversely proportional to altitude.
2017-6-10
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Bill in Ohio
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Levurmion Posted at 2017-6-10 04:41
Of course, my mistake. I mean almost constant. There are obviously factors that contribute to these fluctuations but for the sake of making things simple, I assumed that generally, air pressure is inversely proportional to altitude.

At higher altitudes using 29.97 barometer setting helps everybody avoid hitting each other.  At low altitudes having the proper local barometer setting makes the difference in crashing short of a runway and landing safely in bad visibility.  I assume, that it primarily uses gps for altitude, I don't know if they use  digital terrain elevation data (DTED) or not.  If so, then the AGL would fluctuate over hilly terrain.  If not then, they are just using your elevation at launch, unless maybe you update your home point.
2017-6-22
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Glenn Goodlett
First Officer
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I think it should read altitude above the surface of the moon.
2017-6-22
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jamesw
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Canada
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it's spelled altitude
2017-6-23
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Tealk
Second Officer
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in Romania is 500m max above the home point ... and works fine
2017-6-26
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RocketChap
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hallmark007 Posted at 2017-5-29 06:54
Max altitude is AGL, Not take off point but once whatever ground is underneath the Mavic measures 400ft AGL you are within your guidelines.

There seems to be some debate about this - UK air law (ANO - CAP363) says: "must not fly the aircraft ... at a height of more than 400 feet above the surface" i.e. AGL.  Where as the BMFA handbook (http://handbook.bmfa.org/ page 14) says " at a height of more than 400 ft above the surface .... A further point is that ‘above the surface’ means ‘above the point of launch from the ground’ and this has been clarified with the CAA on several occasions – Ed). "
2017-9-17
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hallmark007
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RocketChap Posted at 2017-9-17 14:26
There seems to be some debate about this - UK air law (ANO - CAP363) says: "must not fly the aircraft ... at a height of more than 400 feet above the surface" i.e. AGL.  Where as the BMFA handbook (http://handbook.bmfa.org/ page 14) says " at a height of more than 400 ft above the surface .... A further point is that ‘above the surface’ means ‘above the point of launch from the ground’ and this has been clarified with the CAA on several occasions – Ed). "

It's not rule here in Ireland , it seems strange if your 400ft AGL but 500ft above take off, surely you can walk or go to the point underneath the 500ft launch from that spot and fly to 400ft and you will be in the same spot and then within legal altitude height, it's hard to make sense out of this, but if them is the rules, what can I say.
2017-9-17
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