In one of my latest flights I noticed 2 problems with AirData ..
The Home point shown is completelly wrong and as a consequence the total flight kilometrage is wrong
AirData Total Kilometrage = 1,108mt
DJI Fly Totale Kilometrage = 559mt
See attached the 2 screenshots...
I also attach the flight log so maybe someone here can analyze it and understand why it did happen (so far is the 1st time I see such type of problems.. after over 70 flights)
DJI Fly version = 1.5.4 (build 1390 official)

Thanks in advance

DJIFlightRecord_2021-12-30_[12-40-40].zip (1.38 MB, Down times: 5)

2022-1-4 Upload

Click on the file name to download attach
Flight log      

AirData UAV - Wrong

Hi,

Easy log to check   ;-)

Flight started with 7 satellites and zero reception, so no LatLon and HP set at start.
So in OPTI mode....

After 13 secs > 8 sats > now LatLon data is recorderd but no HP set!
After 39 secs > finally level 4 for reception, so HP set.

Best to wait and see the GPS icon top right in the fly app turn from red>amber>white.in White : HP is set.

Distance is only calculated when the GPS LatLon is recorded.

cheers
JJB

At

JJB* Posted at 1-4 10:57
Hi,

Easy log to check   ;-)

Hi JJB

are you saying that it is normal what AirData is showing? Or it is their "bug"/wrong analysis? Or maybe the problem is within DJI Fly latest version?

It is the 1st time that I see such discrepance ..

Thanks

spanzetta Posted at 1-4 11:00
Hi JJB

are you saying that it is normal what AirData is showing? Or it is their "bug"/wrong analysis? Or maybe the problem is within DJI Fly latest version?

Hi,

It is normal to show this data as shown, when your drone does not receive GPS data its position is not known for any program like AIrdata etc.

So FlyApp is oke....

So the fault is to start a flight with no GPS reception!

What happend at the end of the flight??  did it crash or ?  
as the last record is in Sport mode + compasserror + Motorblock message

As said distances in the app is calculated from HP. In the chart ; the green line is flown without HP set **, so this distance is not in the total distance ofcourse.
** GPS icon top right showed amber ; LatLon recorded but GPS reception not good enough to set the HomePoint.

Start of the green line is not exaclty your start point, as the LatLon was not recorded at takeoff.
HP set far away from the actual takeoff point, wich can be a distaster when connection is lost! Drone will fly to HP and not to you.....

cheers
JJB

spanzetta Posted at 1-4 11:00
Hi JJB

are you saying that it is normal what AirData is showing? Or it is their "bug"/wrong analysis? Or maybe the problem is within DJI Fly latest version?

are you saying that it is normal what AirData is showing? Or it is their "bug"/wrong analysis? Or maybe the problem is within DJI Fly latest version?
The "bug" is that you were impatient to fly and launched before getting full GPS reception.
The drone had no GPS data to record and no home point until 39 seconds after you launched.

To avoid this in future wait until the home point has been recorded before launching.

Hello there spanzetta. Good day and thank you for the inquiry. Since this is a 3rd party application ( AirData ), I hope that you will get the best information with regards to this matter from our fellow DJI co pilots who have tried using the AirData application.  Just a reminder to please use the DJI Fly application when flying your DJI Mavic Mini for compatibility and reliability purposes. Thank you.

Labroides Posted at 1-4 12:58
are you saying that it is normal what AirData is showing? Or it is their "bug"/wrong analysis? Or maybe the problem is within DJI Fly latest version?
The "bug" is that you were impatient to fly and launched before getting full GPS reception.
The drone had no GPS data to record and no home point until 39 seconds after you launched.

I was in the middle of snow.. that's why I was "impatient" to take off.. from my hands.. and then I waited in hovering that GPS was properly recieved before starting to fly...
I did the same way other times (not always of course) but I never found this Home point wrong position in AirData

I think there is a bug there because.. where did Airdata got the wrong Home Point?
From the log?
In either DJI Fly (reporting wrong/old Home Point) or AirData (interpreting in wrong way the log) there must be a "bug".. otherwise they should both show the same Home Point.. which is not the case..

I hope I was clear enough to explain my point

;-)

JJB* Posted at 1-4 11:57
Hi,

It is normal to show this data as shown, when your drone does not receive GPS data its position is not known for any program like AIrdata etc.
[Image]

The thing is that in DJI Fly the Home Point was correct.. but not in Airdata..
That's why I think to a bug

At the end of the flight it simply hurted my hat and fallen down in the snow .. with no issues fortunately

spanzetta Posted at 1-5 02:41
The thing is that in DJI Fly the Home Point was correct.. but not in Airdata..
That's why I think to a bug

Hi,

In the log HP was set after39 seconds, so don`t know why you think that the HP was correct in the fly-app.
White marker in post #4 is the position of the fly app HP.
As explained, that is why the total distance in less than the flown distance, first part flown without GPS data....

Happy many landings,
cheers
JJB

JJB* Posted at 1-5 03:05
Hi,

In the log HP was set after39 seconds, so don`t know why you think that the HP was correct in the fly-app.

The DJI fly app shows the right HP (yellow circle H).. it is only AirData that shows the long line from a completely wrong position
You see this by comparing the 2 screenshot at my initial post.. it is so clear

spanzetta Posted at 1-5 03:37
The DJI fly app shows the right HP (yellow circle H).. it is only AirData that shows the long line from a completely wrong position
You see this by comparing the 2 screenshot at my initial post.. it is so clear

Uh,

AirData shows the H icon at the point where the first GPS position is recorded.
DJI shows the H icon where the HP was set after 39 sec in flight.

So where did you start your flight ?  near the H icon in the airdata map or near the H icon DJI map ?

According to the flightlog.txt you started the flight near the AIrData "H"

cheers
JJB

I started the flight where DJI Fly app shows the H..
Indeed

That's why I am insisting to say that Airdata had a problem... as if I started the flight from a completely wrong point..

But if the wrong position is in the log.. then the problem is with DJI Fly app.. isn't it?

spanzetta Posted at 1-5 03:53
I started the flight where DJI Fly app shows the H..
Indeed

Hi,
Found the issue.

First  recorded GPS points approx 550 meter apart from each other.  see my chart. (first black dot + see green dots)
This because of the low number of receiving sats at start of the flight, so first position not the actual position!.
Apparantly Airdata uses first GPS position as HP
See chart 2   bottom bar with distance between 2 records....

So no issue with the FlyApp and your flightlog, AirData is not correct.

Mystery solved.

cheers
JJB

spanzetta Posted at 1-5 02:38
I was in the middle of snow.. that's why I was "impatient" to take off.. from my hands.. and then I waited in hovering that GPS was properly recieved before starting to fly...
I did the same way other times (not always of course) but I never found this Home point wrong position in AirData

I did the same way other times (not always of course) but I never found this Home point wrong position in AirData
I think there is a bug there because.. where did Airdata got the wrong Home Point?
I've looked again at the actual data and see why you are confused.
Airdata has done something strange for you
But it's different when I use the same data here.

Your Airdata image does look like there was a homepoint in the north (but according to the data, there never was).
When I upload your flight record to Airdata, it doesn't have an H at that point in the north.
On my computer it calls that Point A.

Here is the explanation:
Your drone started to get aproximate GPS data at 0:13.7.
But it was not accurate so no home point was recorded...
Airdata shows the inaccurate location and labels it Point A.
The drone was never at Point A.

As signals from more satellites were received, the data became more accurate and eventually it was good enough for the flight controller to record a homepoint at 0:39.6.
This is well south of point A.
Airdata confuses by drawing a straight yellow line between Point A and the homepoint.
Why Airdata labelled it H for you is a mystery.

In either DJI Fly (reporting wrong/old Home Point)
It's not possible for DJI fly to have an old homepoint.
When you turn the drone on, it has always lost any old homepoint and the location data is blank until GPS picks up new data.

Ok.. now you both got my point.. great!

But IMHO the problem is also in the log.. why there is the "old" position in the log? (The 550mt far away position is the position of my previous flight)..
Was it "cached"? This should not happen.. isn't it?

If I remember well it didn't take 39 sec to get full satellites and Home Point updated.. but much less (but maybe I am wrong.. it's hard to remember)...

spanzetta Posted at 1-5 07:16
Ok.. now you both got my point.. great!

But IMHO the problem is also in the log.. why there is the "old" position in the log? (The 550mt far away position is the position of my previous flight)..

not cached, this happens when you start a flight with only 7 satellites and zero for reception!
read my post #13, see first few GPS points in your log.
39.2 secs, see data in post#2

Ok JJB.. but is quite strange that with few satellites .. it gets EXACTLY the position of my last flight (that was the position of the Hotel where I stayed) which was about 550 Mt away..
That's why I suspect some kind of caching..

It is too much a coincidence (almost impossible) that when there is few satellite it did get the previous position..
It could have get any other position in any other direction.. but strangely it did get exactly the previous position..

Don't you think it is a strange coincidence?

;-)

I would heed JJB's advice on waiting for the HomePoint to show it is set.  An errant or inaccurate HomePoint could have catastrophic consequences if your drone needed to pilot itself back to the takeoff location in an unfortunate circumstance.

JohnLietzke Posted at 1-5 10:17
I would heed JJB's advice on waiting for the HomePoint to show it is set.  An errant or inaccurate HomePoint could have catastrophic consequences if your drone needed to pilot itself back to the takeoff location in an unfortunate circumstance.

We already discussed that it's only Airdata that did show a wrong Home Point..
DJI Fly did set the correct Home Point even if at take off it was with few satellites

spanzetta Posted at 1-5 08:41
Ok JJB.. but is quite strange that with few satellites .. it gets EXACTLY the position of my last flight (that was the position of the Hotel where I stayed) which was about 550 Mt away..
That's why I suspect some kind of caching..

Yeah, i admit   a really strange coincidence!  and as an engineer i do not believe so much in actual coincidences.

In al the thousends of logs i have seen i never saw a cached LatLon position before.
This would mean that the hardware in the drone remember the last GPS position from a previous flight. Or does the fly app store that data and....  ;-)

Just wait the next time for the GPS icon turns white....

First recorded LatLon in the chart ; looks above trees....next to the hotel ?

cheers
JJB

spanzetta Posted at 1-5 10:44
We already discussed that it's only Airdata that did show a wrong Home Point..
DJI Fly did set the correct Home Point even if at take off it was with few satellites

minor correction ; FlyApp does set the HP when a) enough satellites are received (no hard number for this) and b) signals are "good" enough to set HP.

This is seen in the app when the GPS icon turns into white.

In your flight this at 39 seconds, at that time 8 ssats and in the range 0 - 5 a 4 for i all it quality of reception. (start of your flight 7 sats with 0 for quality).

cheers
JJB

Hi
AirData Flight Path shows extra data from Logs which it shouldn't, DJI Fly and PhantomHelp ignore this data and show Flight Path from first recorded Home Point. Have a look at uploads to see where difference occurs.
Hope this explains why AirData  is different.

spanzetta Posted at 1-5 07:16
Ok.. now you both got my point.. great!

But IMHO the problem is also in the log.. why there is the "old" position in the log? (The 550mt far away position is the position of my previous flight)..

But IMHO the problem is also in the log.. why there is the "old"  position in the log? (The 550mt far away position is the position of my  previous flight)..
Was it "cached"? This should not happen.. isn't it?
Location data is never cached.
After a flight, it is lost completely and the next time when you turn on the drone it has no location data until it gets new data from GPS.

If I remember well it didn't take 39 sec to get full satellites and Home Point updated.. but much less (but maybe I am wrong.. it's hard to remember)...
Recorded data is always more accurate than what you think might have happened.
Here's a little of the actual data rather than the confusing picture that AIrdata painted for you.
Note that:
  there is no GPS location data at all until 13.7 sec
  at 13.7 sec the number of sats is 8 and the GPS Level is 2
GPS Level is an indication of how much the flight controller trusts the GPS data.
It won't trust the data until GPS Level = 4 or 5.
  
The first 4 Lat/Long data points (purple) are very inaccurate and GPS accuracy gets better over time.
This is the way GPS works when you startup and it's normal.

GPS accuracy becomes better and at 0:39.6 sec, when GPS Level = 4 the flight controller records a home point (green)