Serg SSA Posted at 4-9 00:47
Moreover, in fact, the position of your home point has not changed AT ALL, its coordinates have simply been clarified so that in reality they indicate the same point. They were just initially determined with a greater error. Therefore, this does not affect security in any way.That's why there was no message

well, i do not agree with you

If LatLon data is changed in the flightlog, the 2 positions does not point to the same actual location ofcourse.

cheers
JJB

JJB* Posted at 4-9 02:36
well, i do not agree with you

If LatLon data is changed in the flightlog, the 2 positions does not point to the same actual location ofcourse.

The coordinates of the place were initially calculated based on data alone, but after the satellite position was clarified, the same place received new coordinates. It is not the place that has changed, but the calculation of its coordinates based on new data.

Serg SSA Posted at 4-9 02:44
The coordinates of the place were initially calculated based on data alone, but after the satellite position was clarified, the same place received new coordinates. It is not the place that has changed, but the calculation of its coordinates based on new data.

See what DJI explains about this issue, i have some understanding of GPS etc, i do not buy your explanation at all.


cheers
JJB

JJB* Posted at 4-9 03:20
See what DJI explains about this issue, i have some understanding of GPS etc, i do not buy your explanation at all.

Perhaps, when fixing the coordinates of the home point, the drone also remembers the satellite data on the basis of which it calculated the coordinates; after clarifying the data on the position of the satellites, the drone can recalculate the coordinates.
This is just my guess that may explain the situation.
Of course I would like to know an explanation from DJI

The difference is 72cm +/-
Forget the stories about solar activity, almanac...
it looks more like an RC glitch which updates the position of the home point to its own position, automatically.
Why???? no clue!

LV_Forestry Posted at 4-9 05:24
The difference is 72cm +/-
Forget the stories about solar activity, almanac...
it looks more like an RC glitch which updates the position of the home point to its own position, automatically.

totally agree, almanac and solar etc  simple bs.

About the 72 cm plus/minus, as you don`t have the exact LatLon position how do you calculate 72 cm ?
Checked, possible to calculate with using only the number after de dot.
Actual calculate distance = 0.716500144157926 cm   :-)


cheers
JJB

JJB* Posted at 4-9 06:29
totally agree, almanac and solar etc  simple bs.

About the 72 cm plus/minus, as you don`t have the exact LatLon position how do you calculate 72 cm ?

Yes you got it. The two first digit are pretty useless for such calculation.
What is important is to know +/- where you are because for example if i use the same piece of coordinate at the equator, it would give something like 80cm.

I took coordinates near Utrecht to do the calculation.

LV_Forestry Posted at 4-9 07:23
Yes you got it. The two first digit are pretty useless for such calculation.
What is important is to know +/- where you are because for example if i use the same piece of coordinate at the equator, it would give something like 80cm.

yep, my thought as well, depending on were on the globe the accurancy using only decimals varies.
Guess every position picked in my country results to plus/minus 72 cm.

Thanks for getting my memory back in order for this point.

cheers
JJB

JJB* Posted at 4-9 07:34
yep, my thought as well, depending on were on the globe the accurancy using only decimals varies.
Guess every position picked in my country results to plus/minus 72 cm.

Coming back to the subject, if you still have the flight log of my M300 that I put in a tree, you could take a look because I wonder if there wasn't the same kind of glitch.

I mean when the RC link broke, the drone came back nearby the original home point but it was off by some 10 meter. I remember having this discussion with the DJI technical staff.

LV_Forestry Posted at 4-9 07:41
Coming back to the subject, if you still have the flight log of my M300 that I put in a tree, you could take a look because I wonder if there wasn't the same kind of glitch.

I mean when the RC link broke, the drone came back nearby the original home point but it was off by some 10 meter. I remember having this discussion with the DJI technical staff.

Hi,

I have so much logs....and not sorted by name  so if you tell me the log details i can do a search on my database

cheers
JJB

LV_Forestry Posted at 4-9 05:24
The difference is 72cm +/-
Forget the stories about solar activity, almanac...
it looks more like an RC glitch which updates the position of the home point to its own position, automatically.

I do not insist on my version, this was an attempt to find at least some explanation)
It looks like you have a version that you discussed earlier, tell me more, I think it will be useful to many.

Serg SSA Posted at 4-9 11:22
I do not insist on my version, this was an attempt to find at least some explanation)
It looks like you have a version that you discussed earlier, tell me more, I think it will be useful to many.

I am looking for an extremely detailed course concerning the operation of GNSS, I wanted to recommend it to you already last time because you seem interested in the subject.  I'll send it to you when I will find it.  

Your idea would be possible in the case of deferred processing of the receiver data.  A sort of onboard PPK.  But this does not exist to my knowledge.  

The GNSS receiver of a consumer drone is simply capable of receiving signals, processing them, and deducing coordinates, in real time!  
Then the drone and RC software takes care of the rest.  So the only explanation that could lead to this sudden change of coordinates is that DJIfly executes the change home point to RC location function itself, without any action from the operator.

Because coordinates don't come out of nowhere.  These are not those of the drone, but they potentially correspond to that of the RC.
Maybe !

But what is certain is that an error in the almanac wont interfer on previously recorded HP coord

LV_Forestry Posted at 4-9 11:40
I am looking for an extremely detailed course concerning the operation of GNSS, I wanted to recommend it to you already last time because you seem interested in the subject.  I'll send it to you when I will find it.  

Your idea would be possible in the case of deferred processing of the receiver data.  A sort of onboard PPK.  But this does not exist to my knowledge.  

The simplest explanation is some kind of error in Fly, but it doesn’t explain anything... I think DJI won’t explain anything either, they’ll just say install the latest updates.
I would be glad to receive additional information.

Serg SSA Posted at 4-9 12:05
The simplest explanation is some kind of error in Fly, but it doesn’t explain anything... I think DJI won’t explain anything either, they’ll just say install the latest updates.
I would be glad to receive additional information.

Yes, it's a safe bet that it's an error somewhere in the application.  

It is certain that in the event that DJI manages to identify the problem, we will not know anything about it.  Maybe a "minor issue solved" line in the following changelog as they usually do.

Are the APPGPS lat and long columns in the csv populated ?  If so do any changes in them happen to correspond with changes in the Home lat and long columns ?

JJB* Posted at 4-9 00:26
There is not more to find in the data, so no need to share log.

Plus location in log is too private for good reasons for sharing.

If you won't let anyone else look at the data you are on your own.
And no-one would have known that your secret squirrel location was "so private" until you mentioned it.

Serg SSA Posted at 4-9 03:31
Perhaps, when fixing the coordinates of the home point, the drone also remembers the satellite data on the basis of which it calculated the coordinates; after clarifying the data on the position of the satellites, the drone can recalculate the coordinates.
This is just my guess that may explain the situation.
Of course I would like to know an explanation from DJI

The drone doesn't go back and revise GPS locations later in the flight.
And DJI won't be explaining anything.

Labroides Posted at 4-9 14:49
If you won't let anyone else look at the data you are on your own.
And no-one would have known that your secret squirrel location was "so private" until you mentioned it.

haha  i can handle DJI flightlogs better than most people on here...

About the 'squirrel' location, just explaining to you why i do no want to share this log.
And if people see the location, they will understand why it has to be private.

cheers
JJB

Sean-bumble-bee Posted at 4-9 13:48
Are the APPGPS lat and long columns in the csv populated ?  If so do any changes in them happen to correspond with changes in the Home lat and long columns ?

Notthing in these columns, as i can remember columns are empty now for many years.
Before that for some type columns had data in there

cheers
JJB

Hi there, JJB*. If you would like you can send us the Flight Logs and I will forward them to our senior tech support to check. Thank you.

Labroides Posted at 4-9 14:50
The drone doesn't go back and revise GPS locations later in the flight.
And DJI won't be explaining anything.

I think so too, my fantasies were purely theoretical)

DJI Tony Posted at 4-10 00:32
Hi there, JJB*. If you would like you can send us the Flight Logs and I will forward them to our senior tech support to check. Thank you.

Hi Tony,

Do you have email adress or so to sent to, sent me a pm
I have the flightlog and the DAT file.

cheers
JJB

JJB* Posted at 4-10 01:45
Hi Tony,

Do you have email adress or so to sent to, sent me a pm

Hello, JJB*. If it's fine, you can upload it to a cloud storage like Google Drive and then PM me the link. Thank you very much.

I'm pretty sure that I've had my homepoint change just after takeoff (I always wait for GPS first so not sure it should update) but not later in a flight. My drone is a mini 3 pro.
How did you get the detailed log where you can see the homepoint change (firstly it looks interesting and secondly I could pay more attention to having a homepoint and then for it to update).

DJIDronePete Posted at 4-10 04:25
I'm pretty sure that I've had my homepoint change just after takeoff (I always wait for GPS first so not sure it should update) but not later in a flight. My drone is a mini 3 pro.
How did you get the detailed log where you can see the homepoint change (firstly it looks interesting and secondly I could pay more attention to having a homepoint and then for it to update).

Hi Pete,

Flightlog has all the details about many many items, HomePoint data as well.

My own software detects HP changes, so not searching through all records and fields but simply show flight summary.

cheers
JJB    [ Charts by FRAP ; the 'best' software for data and visual flightlog analysis (www.jjbfrap.eu) ]

JJB* Posted at 4-9 22:56
Notthing in these columns, as i can remember columns are empty now for many years.
Before that for some type columns had data in there

Yep, I have had a look at some fly app logs and the App(lati/long) columns were empty ;-(

Did you use RTH on that flight to see if the M4P returned to the launch location or 72cm away from it?

Given that the difference is in the last digit, I am wondering if this is caused by some kind of glitch in the least significant bits. The HP is stored in the drone and I assume it is sending this regularly to the RC. If, at some point, a bit topples over, the reported HP changes and the RC will pick up on this change. Why the bit topples....... no idea, but this scenario would fit your situation where you see the HP change, but without the usual 'Homepoint updated' notifications.

JJB* Posted at 4-10 04:30
Hi Pete,

Flightlog has all the details about many many items, HomePoint data as well.

Hey JJB, I have read about this glitch before, possibly three times with yours...

What I don't remember is if the other two where M4P as well, or the M3P...

If the other two were M3P, then perhaps the latest firmware is the issue...

Burt37 Posted at 4-11 01:19
Hey JJB, I have read about this glitch before, possibly three times with yours...

What I don't remember is if the other two where M4P as well, or the M3P...

perhaps the latest firmware is the issue
People love to blame firmware updates for all kinds of things.
But it's never firmware that's responsible.
I  doubt it is in this case too.

Labroides Posted at 4-11 01:58
perhaps the latest firmware is the issue
People love to blame firmware updates for all kinds of things.
But it's never firmware that's responsible.

So, what's your theory again behind this "glitch"?

I can't find them now, but I'm sure I read another couple of post where people had the same thing happened...

Burt37 Posted at 4-11 02:38
So, what's your theory again behind this "glitch"?

I can't find them now, but I'm sure I read another couple of post where people had the same thing happened...

I can't see the relevant data so I'd only be guessing (and I don't do that).
At only 0.4 metres, it makes no practical difference.
If it was a real difference I'd be interested to get to the bottom of this, but until there are incidents involving a real change, I'm not concerned.

I'm sure I read another couple of post where people had the same thing happened
You might be thinking of this one ....

https://forum.dji.com/forum.php?mod=viewthread&tid=310355

But the OP was quite vague in his description and hasn't shown any interest in solving his mystery.
Without seeing his data it's impossible to tell if it's a real issue or he's just misunderstanding something quite normal.

Labroides Posted at 4-11 02:49
I can't see the relevant data so I'd only be guessing (and I don't do that).
At only 0.4 metres, it makes no practical difference.
If it was a real difference I'd be interested to get to the bottom of this, but until there are incidents involving a real change, I'm not concerned.

Yes, that was the one...

If I got to be honest, My Mini3P has never been very accurate in returning to the exact same spot after a fly. There is always a bit of difference maybe 20-50cm, but I never got an audio message...

We're talking about a difference of less than 1 meter here. That's really not a big problem. Especially since the deviation occurs very rarely. Furthermore, it's always advisable to supervise the landing, so that you can intervene and correct if necessary.

If the deviation were several meters, I could understand the concern...

MKmini4 Posted at 4-11 03:32
We're talking about a difference of less than 1 meter here. That's really not a big problem. Especially since the deviation occurs very rarely. Furthermore, it's always advisable to supervise the landing, so that you can intervene and correct if necessary.

If the deviation were several meters, I could understand the concern...

I think (and agree) that the concern of the OP is the fact that the HP changes without (his) intervention. Without knowledge why, one cannot assume that the distance is always limited....

MKmini4 Posted at 4-11 03:32
We're talking about a difference of less than 1 meter here. That's really not a big problem. Especially since the deviation occurs very rarely. Furthermore, it's always advisable to supervise the landing, so that you can intervene and correct if necessary.

If the deviation were several meters, I could understand the concern...

Hi,

Problem is ofcourse a serious one !
This flight the HomePoint was moved 72 cm away from the original HomePoint, HP changed out of the blue.

Mayby next it will shift away few meters....or more    can you be sure that this will not happen ?

If drone looses connection AND cannot be restored (and this does occur) ....RTH landing can end in a crash, or into water mayby of on a roof of a house  etc ect.
This uncontrolled HP change happend 2x on my drone, and as i fly a lot it happens very rarely...but, as said, it can be a disaster.

cheers
JJB

Burt37 Posted at 4-11 03:17
Yes, that was the one...

If I got to be honest, My Mini3P has never been very accurate in returning to the exact same spot after a fly. There is always a bit of difference maybe 20-50cm, but I never got an audio message...

Hi Burt,

There is a misunderstanding about GPS accurancy, if your GPS is off few meters from the actual takeoff spot and during flight GPS quality remains the same, than it will land on the same spot, often with some cm away from the spot.

But if you look on GE and spot the LatLon....than you see the real offset.

So find a nice spot for launch wich is a good landmark on GE map, and check after flight the LatLon landings data from the log on the map, you will be surprised sometimes.  ;-)

Ofcourse no audio message, as HP data stored in the drone is not changed.

cheers
JJB

Frank071 Posted at 4-11 00:51
Did you use RTH on that flight to see if the M4P returned to the launch location or 72cm away from it?

Given that the difference is in the last digit, I am wondering if this is caused by some kind of glitch in the least significant bits. The HP is stored in the drone and I assume it is sending this regularly to the RC. If, at some point, a bit topples over, the reported HP changes and the RC will pick up on this change. Why the bit topples....... no idea, but this scenario would fit your situation where you see the HP change, but without the usual 'Homepoint updated' notifications.

Hi Frank,

No i did not RTH to check, simply because during this flight i was not aware that the HP was changed.

I noticed this looking in the flightdata, checked the screen recording if i had missed something on the screen.

cheers
JJB

Frank071 Posted at 4-11 00:51
Did you use RTH on that flight to see if the M4P returned to the launch location or 72cm away from it?

Given that the difference is in the last digit, I am wondering if this is caused by some kind of glitch in the least significant bits. The HP is stored in the drone and I assume it is sending this regularly to the RC. If, at some point, a bit topples over, the reported HP changes and the RC will pick up on this change. Why the bit topples....... no idea, but this scenario would fit your situation where you see the HP change, but without the usual 'Homepoint updated' notifications.

Did you use RTH on that flight to see if the M4P returned to the launch location or 72cm away from it?
That wouldn't prove anything.
GPS is not as accurate as you imagine.
Differences of +/- a few metres are common and normal.

Hmmm, tagging this thread to come back later when the discussion about dynamic homepoint comes up again claiming it's a huge miss.

JJB* Posted at 4-9 10:41
Hi,

I have so much logs....and not sorted by name  so if you tell me the log details i can do a search on my database

It was on May 25th 2023.
I found the conversation with the DJI enterprise staff. They simply ruled that the main board and especially the RC system was defective. My question was not really answered regarding the reason for the RTH shift to around ten meters from the homepoint.

For GPS fanatics, I'm talking about a Matrice 300 RTK. Which even when not connected to a real-time correction network, always land in automatic mode with great precision.