Solved: it is ASL! - Is Anafi writing the absolut height in the pictures, or is it height over homepoint? Or is it my barometer?

[Ana789]

I ask, because yesterday I found out, by accident, that the height limitation (150m max) is gone, in case the geofence is off!
I found out about it on a flight up a hill slope.
Calculated just to get up this 150m, but it became 180, 220, 275, ...., 555m in the end
Had to look if there is a 500m limit like with some other drones, I have.
(Don't worry, because of the slope I was in legal height over ground. And I still could see the Anafi, too! ;-)

But looking on the pictures, the height in there is shown as 654m
But I was just 40ish m ASL.

Kind of I assume it is a baro problem.

What to do?

 

[MrDosa]

The height is calculated from the takeoff point not from the ground below.

 

[Ana789]

The height is calculated from the takeoff point not from the ground below.

I thought so, too.
So why did I have such a big difference of about 20% in shown height in freeflight and noted height in pictures?

 

[Jagerbomb52]

I'm not sure if this is the same thing but on one of my other UAV's ( Autel X-Star) if you look at a photos EXIF info it will show the Alt. almost 60-80 feet higher then what the actual flight was.

 

[Ana789]

So, today "I did it again"

Went to a nice location with a slope, made my stops at 50, 100, 150, 200, 250, 300, 350 and 400, as displayed in FF6
But the pictures show:
73, 127, 180, 235, 289, 344, 398, 455m

So it started with about 23m more, as the Anafi shows height in freeflight over HP

I have to admit, I forgot to take a picture at starting height!

but still, and even if it is "only" 55m, this time, it is a interesting and significant difference.

Try to find a location where I know the exact height from the ground to the top, that I can fly, too!

 

[Liger 1956]

Is the Exif data using GPS altitude, which will be above mean sea level plus or minus the vertical GPS error, and the FF6 graph showing barometer altitude which is above take off point?

See here How accurate is the altimeter in a GPS watch for hiking or climbing? for a discussion on vertical GPS accuracy.

 

[Ana789]

Is the Exif data using GPS altitude, which will be above mean sea level plus or minus the vertical GPS error, and the FF6 graph showing barometer altitude which is above take off point?
....

Yes, and that was my question, in the beginning:
Is ANAFI putting the GPS height into the EXIF-Data?

At least one of my DJI isn't doing that!
I checked on a picture I have taken there, starting from the top of the hill.
Today I used the slope from said hill, to "climb" up from the ground.
The picture with the DJI says 40ish meters, where the exif of the Parrot tells me 450ish

So I take it, the EXIF is from GPS, inaccurate, perhaps
The barometer then should give me altitude over starting point, most correctly.
Right?

 

[Liger 1956]

Could you take a photo about 1m above the take off point then use an app on your phone to see what the gps height is? That should tell you whether it is the barometer, if the Exif altitude is 1m, or the GPS, if the Exif altitude compares with the phone app figure, that is recorded. If you know the height of the hill above the surrounding land then you can check with FF6 the altitude at the base, which I assume will be about zero, and then carry the Anafi to the top of the hill whilst powered up, be carefull!, and check the FF6 altitude again. Assuming that FF6 reports the barometric altitude then the reported altitude should be the height of the hill.

I have never done this so I cannot be sure that the Anafi will update the altitude without it being in flight.

 

[Jagerbomb52]

I started going through some very old posts on another forum that basically the same topic came up for a different brand of UAV. Here is what one fellow stated. I have no idea if its true or not but sounds about right.
" GPS does not tell the quad it's altitude. Altitude on all prosumer UAV's is determined by the barometer. It may also be showing height above sea level.. "

 

[Ana789]

I wrote, a bit earlier, I forgot the picture at start (height)
My bad

Will try to do that next time! ;-)

But a 20/30 ish ASL can be right, for the HP
To the hilltop I don't get reliable height info, that is a difference between 370ish and 540m, all I can google about.
But I know for sure, that it is a lot less as the highest hilltop around, which should be around 530m.
And a elevation map gets me a calculated 420ish meter to the top of the building on top of it.
Just my 400m (FF6 in app height) lets me already look at it from a bit above!

So I'd say that the 455m from the EXIF can be the real height
And that said, taking in account I started on 20-25ish(guessed from the 73m/exif on 50 m/FF6, stop one), the barometer is giving a just under 10% wrong height info.

I can deal with that, setting the max height 10% under the legal height, if needed, shouldn't be tooo difficult!

 

[Ana789]

I started going through some very old posts on another forum that basically the same topic came up for a different brand of UAV. Here is what one fellow stated. I have no idea if its true or not but sounds about right.
" GPS does not tell the quad it's altitude. Altitude on all prosumer UAV's is determined by the barometer. It may also be showing height above sea level.. "

Shall we ask Parrot, then?
Someone has to know, where the Anafi is getting the exif-height data from

 

[Jagerbomb52]

Shall we ask Parrot, then?
Someone has to know, where the Anafi is getting the exif-height data from

I would normally say thats a good idea but after having some dealings with their customer support I say good luck on getting a educated answer LOL

 

[Jagerbomb52]

One option you might have is asking your question in the developers forum. Sometimes you will get a response from a real tech that actually knows his stuff.

Parrot Developers Forum

Parrot Developers Forum

forum.developer.parrot.com

 

[Ana789]

I think, I will start a flight just ASL and do some pictures every couple of meters
Perhaps I'll do that in a flight plan.
Will see and report back!

 

[Jagerbomb52]

A Google search using Altitude vs. exif data quickly shows that this problem is not exclusive to the Parrot Anafi, as the DJI Phantom Forums have been hotly debating it for years.

 

[Ana789]

But isn't there problem that they wanna connect all the dots?
ASL to AGL , compared to the height over starting point?

I just wanna know, the easy way, right mouse click, properties, if it's flight height or absolute.
(Right now ;-)

And I just realize that I only have this problem b/c my last checked flight pictures have been all taken from flights with 20-50m starting height.

So I was (not only, methinks) confusing myself!

Checking on different locations is telling that the height in the Anafi-EXIF has to be absolute height above sea level

So:
Anafi is NOT saving the flight height over the starting point in the pictures, but the absolute altitude, from GPS reading.

My apology for not seeing that before I opened this topic!

 

[Ana789]

Conclusion:

FF6 is showing during flight and in the graphic the altitude above starting point

In the stored exif of the pictures it is ASL

Why I started with a difference of approx 40-50ish m (ASL to HP) meters, and ended up about 50 meters higher (100m difference between max altitude ASL/Altitude over HP) is not (yet) to reveal.
Aside that I do not often have flight profiles/heights over HP like this!

thanks for following

 

[Liger 1956]

I am glad that you have sorted that out. Thanks for doing the research and testing.