Calibrating Mavic GPS

PaulS · May 25, 2017

Is it possible to calibrate the Mavic's GPS coordinates using the software ?
I want to take the Mavic to a known survey point and correct the on board GPS coordinates to match the known survey point's coordinates.
Currently the Mavic's GPS coordinates don't match the survey point accurately and they also change every time the Mavic is powered down & up again.

msinger · May 25, 2017

PaulS said:
Is it possible to calibrate the Mavic's GPS coordinates using the software ?

No.

HFMan · May 25, 2017

How far "off" is the position? There literally are no consumer grade GPS receivers that require or even offer calibration.

dmyers7 · May 25, 2017

The inaccuracy you see is built into the satellite system on purpose and yes you will see it drift every time you power up. Surveyors use a differential system to observe the difference between two systems and averages that difference to get better accuracy. The surveyor point is used to further correct by being in a known spot and transmitting a correction for the error to surrounding GPS equipment like the differential system; but this is not a calibration as the error is always changing. So no, you can't and don't calibrate a GPS system. The amount of satellites and obstructions and effect the accuracy. Are you seeing a large difference? Should not be more then a few feet at most with 8 or more satellites. The VPS augments this further when used correctly.

beachcombing · May 28, 2017

dmyers7 said:
The inaccuracy you see is built into the satellite system on purpose ...

"Built into the satellite system on purpose"?

Based on what? Selectively Availability was turned off a long time ago.

dmyers7 · May 28, 2017

"The United States government currently claims 4 meter RMS (7.8 meter 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS. Vertical accuracy is worse. Mind you, that's the minimum. Some devices/locations reliably (95% of the time or better) can get 3 meter accuracy."

Kilrah · May 28, 2017

GPS accuracy can be improved using DGPS or better RTK, which use fixed stations with precisely known location in the vicinity as reference. But the devices need to be designed with hardware and software support for that in mind, you can't just take a random thing like the Mavic and send it correction data.
An RTK receiver alone typically costs as much as an entire Mavic.

beachcombing · May 28, 2017

dmyers7 said:
"The United States government currently claims 4 meter RMS (7.8 meter 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS. Vertical accuracy is worse. Mind you, that's the minimum. Some devices/locations reliably (95% of the time or better) can get 3 meter accuracy."

Right. But the signal is not purposely degraded. This is a limitation of receiver accuracy not system degradation. It's not inaccurate "on purpose".

dmyers7 · May 28, 2017

I concede my facts where a bit scrambled.

pjd900 · Jun 25, 2017

When auto landing using RTH, my Mavic is consistently off by approx 30 feet from its take off location.

Even when a precision take off point has been recorded, it is unable find that area with its visual sensors when attempting to land.

I received this refurbished Mavic from DJI CARE REFRESH. My first Mavic was spot on every time.

Reading these posts, I suppose I already have my answer, but is there no way to improve this issue? Anyone else have this problem and found a way to solve it?

msinger · Jun 25, 2017

pjd900 said:
is there no way to improve this issue?

Did you try calibrating the sensors?

pjd900 · Jun 25, 2017

Thanks for replying. Yes, I've done all the calibrations--VPS, IMU, and compass. No change in performance.

msinger · Jun 25, 2017

Can I take a look at one of your flight logs where the precision landing did not work? If so, please upload it here and post a link back here.

Steveyg777 · Sep 2, 2017

I a total noob but if be tempted to request another mavic from dji

JustinVV · Sep 3, 2017

dmyers7 said:
The inaccuracy you see is built into the satellite system on purpose and yes you will see it drift every time you power up. Surveyors use a differential system to observe the difference between two systems and averages that difference to get better accuracy. The surveyor point is used to further correct by being in a known spot and transmitting a correction for the error to surrounding GPS equipment like the differential system; but this is not a calibration as the error is always changing. So no, you can't and don't calibrate a GPS system. The amount of satellites and obstructions and effect the accuracy. Are you seeing a large difference? Should not be more then a few feet at most with 8 or more satellites. The VPS augments this further when used correctly.

There is no error introduced on purpose any more. That was turned off 17 years ago.

It's just normal atmospheric and clock errors. All GPSS suffer.

The L1 wavelength is 19cm so you will never get better that this whatever you do unless you use other higher frequency signals or corrections.

BuzzyOne · Sep 3, 2017

Regarding RTH accuracy: FWIW, I see a correlation between light and shadows and landing accuracy. I fly out of a very wooded area. The launch area is just a carved out hole in the forest. So by the time I land, 20 minutes has passed and shadows have moved and now the take off spot looks totally different. When I use a contrasty landing pad in a spot that has steady lighting the MP will hit the pad every time (after doing precision take off).

The MP always finds the hole in the forest from 120 meters when returning, but when shadows move over or away from the take off point, it misses the landing point by many feet.

YMMV