Where is the drone? Said my GPS.

[FearlessRobb]

I got over 27 minutes. Flew around till critical low battery and then hovered 2 feet off the ground till battery was at 1% and landed. But it's not recommended to do that. I try to land with 20% to 30% left in the tank.

I land with 12-15% then charge next day if im gonna fly that day. Or if im not gonna fly for a few days ill land at 30% and then charge morning of or day before. I read never recharge right away

 

[Dragonfly]

The US GPS and Glosnass satalite position system is based on two types of output. 1 being military use and the 2nd being civilian use.
The cilvilian systems have a purpose-built error built in of upto 15 meters (approx 45feet) and is not constant. In the most part it can be down to a meter or drift out to the 15 meters in any direction at any time.
It doesnt do this in seconds but rather over a period of minutes so when your Mavic is travelling at any speed it will account for change but if hovering it would move about that change.
What stops it from doing so is the VPS and multiple hundreds of calculations of where it just was as to where it should be now to the change in GPS co-ordinates and if the Mavic is travling at any speed or not.
So while the VPS is holding your Mavic in one spot the GPS position is changing by anything upto 15 meters in any direction from its rough point (ie could be 12 meters North of Mavic then 10 meters East of Mavic so you get 22 meters/66feet of travel) over time say your 20 minutes of flight in a hover you may get 80 to 100 meters/240 to 300+feet of travel and yet Mavic hasnt moved.

Hope this clears it up.

 

[wsteele]

The US GPS and Glosnass satalite position system is based on two types of output. 1 being military use and the 2nd being civilian use.
The cilvilian systems have a purpose-built error built in of upto 15 meters (approx 45feet) and is not constant. In the most part it can be down to a meter or drift out to the 15 meters in any direction at any time.
It doesnt do this in seconds but rather over a period of minutes so when your Mavic is travelling at any speed it will account for change but if hovering it would move about that change.
What stops it from doing so is the VPS and multiple hundreds of calculations of where it just was as to where it should be now to the change in GPS co-ordinates and if the Mavic is travling at any speed or not.
So while the VPS is holding your Mavic in one spot the GPS position is changing by anything upto 15 meters in any direction from its rough point (ie could be 12 meters North of Mavic then 10 meters East of Mavic so you get 22 meters/66feet of travel) over time say your 20 minutes of flight in a hover you may get 80 to 100 meters/240 to 300+feet of travel and yet Mavic hasnt moved.

Hope this clears it up.

Well, not exactly. GPS as originally designed had a precise military signal and an intentionally distorted civilian signal. In the early 2000's an innovation called differential GPS reduced the errors to the civilian signal to that approximating the military accuracy. As a result, the intentional distortion of the civilian signal was turned off about 2002 and has never been turned back on. Now, even without differential GPS and an inexpensive antenna (think cell phones and drones) one should see horizontal accuracy of 9 to 30 feet.

I'm not a heavy user of my Mavic or Spark drones and I have not tested hovering in a static position, but I use RTH extensively and my drones always return to a point overhead within 30 feet of my original home point and then land.

There must be another answer for errors in excess of 300 feet.

 

[Dragonfly]

@wsteele, Civilian GPS has never been turned off, dont know where you got your info from. First military GPS is accurate down to mm and they dont wont civilians with thag typs of accuracy. The type of differental you are referring to came about not from the Sats or the system been altered but from land based stations been erected with very accurate know positions that then calculated the error in the received Sats positions and corrected it giving an accuracy to a foot.
As I said in my first reply the cilvian accuracy of GPS is nomaly upto 15 meter /45 feet but on average is only 3 to 5 meters.
We would never ever be allowed or ever have acces to millitry GPS frequency as civilians.
Plus in a time of dire confict they need the ability to shut of the cilvilan side to protect misuse but still have the other for guidance of ordinance.

 

[Xtreme Drone Pilot]

Plus in a time of dire confict they need the ability to shut of the cilvilan side to protect misuse but still have the other for guidance of ordinance.

Does this mean if the nuclear war starts, we'll have to fly our Mavics in ATTI mode?

 

[wsteele]

@wsteele, Civilian GPS has never been turned off, dont know where you got your info from. First military GPS is accurate down to mm and they dont wont civilians with thag typs of accuracy. The type of differental you are referring to came about not from the Sats or the system been altered but from land based stations been erected with very accurate know positions that then calculated the error in the received Sats positions and corrected it giving an accuracy to a foot.
As I said in my first reply the cilvian accuracy of GPS is nomaly upto 15 meter /45 feet but on average is only 3 to 5 meters.
We would never ever be allowed or ever have acces to millitry GPS frequency as civilians.
Plus in a time of dire confict they need the ability to shut of the cilvilan side to protect misuse but still have the other for guidance of ordinance.

Please don't get too excited. I negotiated the first international agreement regarding use of GPS in the early 80's. I did have pretty good knowledge of the technical design of both the military and civilian signals; but, I will not pretend I'm current on the technology.

1st, I did not infer that they have turned off the Civilian GPS signal, just the intentional degradation of the civilian signal. They reduced the degradation in 1991 during the first Gulf War because there were few military GPS receivers available and the military had to rely on commercial GPS receivers (and only about 10 satellites) that only received the civilian GPS signal. They reinstituted the intentional degradation policy of the civilian GPS signal after that war.

2nd, You're correct that the FAA and others developed and implemented differential GPS technology in the late 90s. A ground station at a known location measured the intentional position errors broadcast by the GPS satellites and broadcast the error correction to the DGPS Receivers giving them near military accuracy. Essentially all aircraft and marine GPS receivers used this differential GPS technology (WAAS) to get accuracies to 10 feet and less. I routinely get this accuracy with my WAAS Marine receiver and just 5 GPS satellites. With the world wide implementation of WAAS technology the US government saw little value for it's intentional degradation of the civilian GPS signal and about 2001 stopped degrading the signal.

Now, I believe (opinion, not fact) that most small electronics use only the GPS technology rather than DGPS (WAAS) and the US government states the 95% accuracy is 25 ft or less. As a side note, the U.S. does reserve the right to degrade the GPS signal again, but with GLONASS and other satellite navigation alternatives available it's extremely unlikely.

Now, back to the original issue regarding why this Mavic was seeing position errors in excess of 300 feet while hovering stationary and receiving signals from 10 or more satellites. I don't think it is externally caused. Logically, one would believe there is an internal error in the GPS processing code on the Mavic or an error between the Mavic, controller, or the DJI Go 4 application regarding GPS positioning.