Return to Home points way off.

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I've seen a lot of posts on this forum about Home Points being way off, and Drones just flying away to a new location. The general consensus is that it is a DJI Firmware or Go App problem. Well, that may be. But let me tell you of a problem I'm having with GPS in general that sounds very much like the problem us done flyers are having. In my work I use a smart phone with GPS navigation to locate my customers when I revieve a service call. It is part of our program. I get an address, and then a Radio Button that says "Map". I select map and it takes me to Google maps and plans my route by the shortest way. We have used it for years now without problems.

But in the last few months I have noticed errors in location by as much as 10 miles. Generally it is only about 1 mile off. Twice in the last week I have been directed by GPS to a supposed customer location. In one case I ended up going as directed down a muddy dirt road south of Olancha California looking for the fire station. When the GPS said, "You have arrived", I found myself looking at open desert with a lone fence post and a big hole in the ground. I continued on down the road until I reached payment and then asked directions from a local man standing in his yard. I was on the correct street, but just 1 mile short of my destination. And I should have come in on a different paved road through the town of Olancha.

And then today, it happened again. I was being directed by GPS to an address on 67th street West in Mojave California. I was directed 10 miles south of town and then told to turn west and go 8 miles to 67th Street West. I did as directed. I was then told to turn left on 67th street and go 1/4 mile. I did! Again, I ended up in open desert in the middle of nowhere.

I ended up calling the customer for directions, only to find out that GPS took me 10 miles to the south of where I needed to be. If our drones used the same GPS system, that might explain some of the Return to Home problems being posted on this forum. I don't know that it make a difference, but my phone is an Android phone. Two bad locations in one week now makes me very suspicious of the directions when using GPS.
 
That's a problem with the turn-by-turn navigation software, not necessarily GPS on your phone. That being said, smartphone GPS isn't especially accurate. It's good enough to know you're on a particular road, but it relies heavily on cell tower locations and the names of WiFi networks to pinpoint you more

The GPS on a Phantom is far more accurate than the GPS on a phone
 
Interesting find!
My question is though, why would version 3.1.2 of the GO app show my tablet's location 3.2 miles away in the same direction as others have seen, and version 3.1.1 show me where I was?
Same tablet, about 10 minutes time difference.
Using my tablet's gps, no AC.
I was able to repeat the same problem also between the two different versions of software.

Could be that the GPS "module" (for lack of a better word) that GO and phones use, have this problem? By module, I mean software for determining the GPS data, not the hardware since that doesn't change with software versions.
 
Could be that the GPS "module" (for lack of a better word) that GO and phones use, have this problem? By module, I mean software for determining the GPS data, not the hardware since that doesn't change with software versions.
I don't think this is right.

The AC has a GPS receiver itself (which it must have, in order to know it's location while flying). When returning to the home point, it is using its own GPS, not the GPS hardware in the phone/tablet on the RC.

Which GPS source it uses when setting the home point is a different matter. I can't imagine that it's using the phone/tablet GPS, as this would set the home point where you're standing, not where the AC is. I've been quite a ways away from my P4 when DJI GO tells me the homepoint has been updated, yet when returning with a manual RTH, is always lands within a few feet of where it took off -- not 20 yards away where I was standing under a tree in the shade.

So, I expect the home point is sensed by on-board GPS, stored on-board, and the firmware does navigation back to the stored HP sensing position with the on-board GPS.

Whatever problem there is is all in the bird, UNLESS DJI GO software sets the homepoint by reading telemetry from the AC then sending coordinates to the AC to store as the HP -- a process in which DJI GO has the opportunity to screw up what the AC sent it.
 
If if the home point is reset by the software, there could be some interaction between the aircraft GPS position and where the app "thinks " the new home point is because the app is interpreting the locatin from the bird and displaying it on the monitor map. A glitch in the algorithm could send confused signal to the AC.
 
If if the home point is reset by the software, there could be some interaction between the aircraft GPS position and where the app "thinks " the new home point is because the app is interpreting the locatin from the bird and displaying it on the monitor map. A glitch in the algorithm could send confused signal to the AC.
Not sure I'm following you...

Only the AC has any ability to sense where it is. Also, because RTH must work with no connection back to the RC, the home point coordinates must be stored on the AC when it takes off.

So this behavior MUST be driven by parameters, and software running on the AC. The only way the app back at the RC could cause this error would be if it deliberately changed the RTH behavior or home point while in flight, which seems to me requires affirmative action on the part of the pilot in the app to initiate a change to home point while in flight.

That is, unless there is a bug in the app that is doing this WITHOUT action on the part of the pilot commanding it to. I would think, though, that would show up in the logs.
 
Only the AC has any ability to sense where it is. Also, because RTH must work with no connection back to the RC, the home point coordinates must be stored on the AC when it takes off.
So why do different versions of GO on an Android tablet/phone mess up the home point?
The AC isn't changing it's FW with tablet/phone version changes?
Maybe the buggy version of the GO app is sending trash data to the AC and overwriting the HP data in the quad?
IOW... what is changing the AC's HP location?
Interesting problem!
(edit)... and you can tell the AC to change it's HP location from the remote. Yes, it is still stored in the AC so that it can RTH without a link back to the remote, but the remote "tells" the AC to set a new home point, NOT actually send the HP data (or at least it isn't supposed to)
 

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