Real agl ?

[scro]

Anyone noticed that the EXIF data in still images has an altitude stamp? However the value doesn't match the altitude displayed in the app. It might be an uncalibrated altitude straight from the mini's barometric sensor as it seem to be vaguely similar to altitude above sea-level. It won't know the current atmospheric pressure so perhaps it has a nominal value for this. When you take off the app will be able to get a barometric reading to use for 0m altitude for that flight.

 

[Meta4]

Anyone noticed that the EXIF data in still images has an altitude stamp? However the value doesn't match the altitude displayed in the app. It might be an uncalibrated altitude straight from the mini's barometric sensor as it seem to be vaguely similar to altitude above sea-level. It won't know the current atmospheric pressure so perhaps it has a nominal value for this. When you take off the app will be able to get a barometric reading to use for 0m altitude for that flight.

Yes ... this is well known and used in photogrammetry.
It's a rough approximation of height above sea level and can be +/-200 feet or more.

 

[chriscuk]

Seems odd that the CAA show a vertical line for height in one, a straight line in the other and every other diagram shows a "bubble".
It seems that if you fly over the endge of a cliff you've got to drop in height massively the moment you get to the edge. Seems a bit different from what all of the various diagrams show or their wording.

 

[sar104]

Without having an inspector up there on a long ladder with a long measuring tape, no-one is likely to ever be able to tell the difference anyway.

It matters significantly in mountainous terrain, when compliance in the vicinity of vertical terrain potentially becomes an issue. There has been frequent discussion of whether an effective 400 ft rule, similar to the Part 107 allowance around structures, applies in those cases. Under the old CAA interpretation that would be true, while under the FAA interpretation it is not.

 

[sar104]

Anyone noticed that the EXIF data in still images has an altitude stamp? However the value doesn't match the altitude displayed in the app. It might be an uncalibrated altitude straight from the mini's barometric sensor as it seem to be vaguely similar to altitude above sea-level. It won't know the current atmospheric pressure so perhaps it has a nominal value for this. When you take off the app will be able to get a barometric reading to use for 0m altitude for that flight.

To expand on @Meta4's comment - it is either the AMSL altitude estimated from the barometric pressure and a standard atmospheric model or the GPS altitude, depending on aircraft and firmware. There is a detailed explanation here:

Firmware v01.00.0510 EXIF altitude changes

A number of people have noted that the latest firmware has changed the EXIF altitude data, but DJI did not specify exactly what had changed. I guessed that it was what I had been bugging them about – namely that the altitude data fields were mis-labeled, e.g. : GPS Altitude Ref ...

mavicpilots.com

 

[nafisgal]

Do not lie ... The maximum flight height of a drone (stipulated by ICAO - ICAO International Civil Aviation Organization) is stipulated internationally at 400 ft / 120 m high ... AGL ..
(measured from the takeoff point).
And the maximum Altitude (AMSL) above sea level, to which a drone can be flown without compromising its structural performance ... is stipulated by most manufacturers, at 9850 ft / 3000 m AMSL altitude.
Without more ...
If I went to Boundary Peak, Nevada (over 13,000 ft / 4000 m) AMSL and raised my drone 400 ft / 120 m. AGL in a radius of 1600 feet / 500 miles (SM) ... there would be nothing illegal ... but you would be compromising the performance of my aircraft / drone ..

 

[Bbarr]

So if I understand, I live in western Co. If I climb up Mt. Sneffles @ 14000 msl. I can fly over Telluride @ 14400 ft ?

 

[The Editor]

Do not lie ... The maximum flight height of a drone (stipulated by ICAO - ICAO International Civil Aviation Organization) is stipulated internationally at 400 ft / 120 m high ... AGL ..
(measured from the takeoff point).
And the maximum Altitude (AMSL) above sea level, to which a drone can be flown without compromising its structural performance ... is stipulated by most manufacturers, at 9850 ft / 3000 m AMSL altitude.
Without more ...
If I went to Boundary Peak, Nevada (over 13,000 ft / 4000 m) AMSL and raised my drone 400 ft / 120 m. AGL in a radius of 1600 feet / 500 miles (SM) ... there would be nothing illegal ... but you would be compromising the performance of my aircraft / drone ..

What on earth are you talking about?

ICAO absolutely DO NOT SET countries UAV operational ceilings. That is up to the individual countries Aviation Authority.
Certain countries whilst allowing UAVs to operate actually have no maximum agl stipulation.

Your second point is also wrong. You only have to take DJI’s Inspire 2 as an example which has an operating ceiling of 5,000m AMSL by simply swapping to HA props. Even the Inspire 1 which has been around since 2015 will operate up to 4,500m AMSL.
The Phantom4 RTK will operate at 6,000m!
Mavic Air - 5000m
Mavic Pro - 5000m
Even the Spark is specified up to 4000m.
Other high altitude UAVs are readily available.

 

[Thomas B]

So if I understand, I live in western Co. If I climb up Mt. Sneffles @ 14000 msl. I can fly over Telluride @ 14400 ft ?

yes, but you must stay w/in 400’ of the ground... and don’t fly over groups of people there

 

[Bbarr]

Sorry for being ignorant. But if I launch at 14000 ft and T ride is at 12000 ft, how do I know the agl of the AC ?

 

[Thomas B]

Sorry for being ignorant. But if I launch at 14000 ft and T ride is at 12000 ft, how do I know the agl of the AC ?

TO point altitude is shown and logged as zero. You’ll be flying down to a negative altitude in the case you suggest.
Keep in mind that 400’ rule still holds as far as above the ground below you.

 

[Bbarr]

Never mind I understand . I cannot fly without Vlos ! Seems here I always fly down ,
Sorry

 

[Bbarr]

So , thank you all.
There is no way for the pilot to know the actual AGL of the AC ...
True ?

 

[Airborne_Aircrew]

So , thank you all.
There is no way for the pilot to know the actual AGL of the AC ...
True ?

No, there is not. Similarly it is very difficult for an observer to assess the AGL unless it is painfully obvious - the "fly over a cliff example"...

The Exif data is based upon the GPS altitude unless it is in variance with every other GPS aware camera in the world and is therefore giving you AMSL, (Above Mean Sea Level), which gives you little clue as to your AGL. Someone else who isn't your friend could take the data from the video and show on a map that your AGL exceeded 400' but you'd have had to have committed a fairly egregious breach of flight rules or pissed off some idiot that won't let go.

From a safety perspective, if you were to fly off the edge of a cliff that is 2000' straight down and take it out 200m you aren't endangering a whole lot of pilots flying full size aircraft or helicopters because they won't be that close to a 2000' cliff unless they are Search and Rescue in relatively good flight conditions. So, really, if you are close to vertical structure you are not going to be in conflict with any other non-drone aircraft.

 

[sar104]

No, there is not. Similarly it is very difficult for an observer to assess the AGL unless it is painfully obvious - the "fly over a cliff example"...

The Exif data is based upon the GPS altitude unless it is in variance with every other GPS aware camera in the world and is therefore giving you AMSL, (Above Mean Sea Level), which gives you little clue as to your AGL. Someone else who isn't your friend could take the data from the video and show on a map that your AGL exceeded 400' but you'd have had to have committed a fairly egregious breach of flight rules or pissed off some idiot that won't let go.

From a safety perspective, if you were to fly off the edge of a cliff that is 2000' straight down and take it out 200m you aren't endangering a whole lot of pilots flying full size aircraft or helicopters because they won't be that close to a 2000' cliff unless they are Search and Rescue in relatively good flight conditions. So, really, if you are close to vertical structure you are not going to be in conflict with any other non-drone aircraft.

Only the Mavic 2 on recent firmware puts GPS altitude into the EXIF. All previous versions used barometric-pressure-derived AMSL. Not sure about the Mini.

 

[Airborne_Aircrew]

Only the Mavic 2 on recent firmware puts GPS altitude into the EXIF. All previous versions used barometric-pressure-derived AMSL. Not sure about the Mini.

How are they determining AMSL, (QNH), by barometric pressure? It only knows the barometric pressure at the point of take off - the QFE, (Field Elevation), the point of takeoff - which is a relative altitude not an absolute altitude based on a standard - Mean Sea Level. Since pressure varies constantly without the ability to derive the QNH via some external method, (internet connection or whatever), it can't know the QNH at it's current location. With that in mind I'd gamble on exif data using GPS data which is, effectively QNH, rather than QFE or the takeoff altitude. This is why you can easily show a negative altitude if your drone drops below it's take off point. If it was AMSL you'd be pushed to get a negative altitude unless your drone was also a submarine.

Does that make sense?

 

[sar104]

How are they determining AMSL, (QNH), by barometric pressure? It only knows the barometric pressure at the point of take off - the QFE, (Field Elevation), the point of takeoff - which is a relative altitude not an absolute altitude based on a standard - Mean Sea Level. Since pressure varies constantly without the ability to derive the QNH via some external method, (internet connection or whatever), it can't know the QNH at it's current location. With that in mind I'd gamble on exif data using GPS data which is, effectively QNH, rather than QFE or the takeoff altitude. This is why you can easily show a negative altitude if your drone drops below it's take off point. If it was AMSL you'd be pushed to get a negative altitude unless your drone was also a submarine.

Does that make sense?

It just uses a standard atmospheric model that gives temperature and pressure as a function of altitude. So by measuring pressure it can estimate AMSL with that assumption of a standard atmosphere. If the prevailing atmospheric conditions deviate from the standard, which in general they will, the derived altitude will not be correct. For example, if you are at sea level and there is a local high-pressure system, it will actually start negative.

International Standard Atmosphere - Wikipedia

en.wikipedia.org

 

[Airborne_Aircrew]

That standard isn't used for actual flight of anything. The ICAO version, (as with the entire thing), is simply a theoretical model that might help aircrew to try to predict potential pitfalls ahead of them. For them to use it in flight as a measure of altitude is utterly suicidal.

If DJI was putting ISA derived altitude into the exif of photos on _any_ of their products I would be past shocked simply due to the fairytale nature of the data especially if the aircraft has GPS data available when most cameras are familiar with using GPS data.

Any attempt to determine AMSL by using the current local barometric pressure is impossible because so many things, including the barometric pressure itself, change - even windspeed locally affects pressure. You said yourself that a pressure below 1030.25 at sea level in using the ISA model would result in a negative altitude AMSL which might be useful for a submariner but not an aviator... ;-)

 

[Meta4]

If DJI was putting ISA derived altitude into the exif of photos on _any_ of their products I would be past shocked simply due to the fairytale nature of the data

So be shocked:

 

[sar104]

That standard isn't used for actual flight of anything. The ICAO version, (as with the entire thing), is simply a theoretical model that might help aircrew to try to predict potential pitfalls ahead of them. For them to use it in flight as a measure of altitude is utterly suicidal.

If DJI was putting ISA derived altitude into the exif of photos on _any_ of their products I would be past shocked simply due to the fairytale nature of the data especially if the aircraft has GPS data available when most cameras are familiar with using GPS data.

Any attempt to determine AMSL by using the current local barometric pressure is impossible because so many things, including the barometric pressure itself, change - even windspeed locally affects pressure. You said yourself that a pressure below 1030.25 at sea level in using the ISA model would result in a negative altitude AMSL which might be useful for a submariner but not an aviator... ;-)

Maybe I wasn't clear on that point. DJI does put barometrically-derived altitude AMSL into the EXIF dat under some older and some current firmware versions. That's not a guess - it's a demonstrable fact. As for being useful to an aviator - I'm not aware of any aviators using EXIF for navigation purposes.