Bizarre GPS readings while flying indoors

[TomSull]

After getting my Mini 2 and wanting to play with it, I did a few tiny flights in my living room late at night (I have high cathedral ceilings). It appeared I was NOT getting a GPS signal, unless I brought the AC over to the glass doors going out onto the deck, and then I might get a signal, but typically not. So I did a few flights, getting GPS warnings for each one, but it was well lit inside. I DID have it start weirdly drifting at one point and I pulled it back.

Later, I looked at AirData, and the GPS info was WAY off by 100s to 1000s of feet. It looked like I'd been out night flying, with a home point at my house but the flight in it's entirety about 1000 feet away, with no LEG of the flight connecting to the home point. Here some screen shots from Airdata:

I filed a bug with AirData, but they came back and said that IS the GPS data from the logfile. SO, does the Mini2 have bad accuracy issues when the GPS is low? I HAVE seen it move on its own 2 or 3 times unexpectedly. Each time, I was watching and corrected the movement. Could it be an issue with THIS Mini 2?

Any advice on how to evaluate if I have an issue or not?

Is this normal with weak GPS?

Thanks!

 

[Phantomrain.org]

After getting my Mini 2 and wanting to play with it, I did a few tiny flights in my living room late at night (I have high cathedral ceilings). It appeared I was NOT getting a GPS signal, unless I brought the AC over to the glass doors going out onto the deck, and then I might get a signal, but typically not. So I did a few flights, getting GPS warnings for each one, but it was well lit inside. I DID have it start weirdly drifting at one point and I pulled it back.

Later, I looked at AirData, and the GPS info was WAY off by 100s to 1000s of feet. It looked like I'd been out night flying, with a home point at my house but the flight in it's entirety about 1000 feet away, with no LEG of the flight connecting to the home point. Here some screen shots from Airdata:

I filed a bug with AirData, but they came back and said that IS the GPS data from the logfile. SO, does the Mini2 have bad accuracy issues when the GPS is low? I HAVE seen it move on its own 2 or 3 times unexpectedly. Each time, I was watching and corrected the movement. Could it be an issue with THIS Mini 2?

Any advice on how to evaluate if I have an issue or not?

Is this normal with weak GPS?

Thanks!

The issue is most likely with the Air Data as there will be updates from them as they work on there profiles.
The best way to test your GPS is simply place the drone by the window, you should get on average 14 to 20 sats , which is fine ,
you only need 3 to fly in the home .

Here is the Phantom 4 flying with 3 Sats.

Phantomrain.org
Gear to fly your Mini 2 in the rain.

 

[THE CYBORG]

I wouldn't expect accuracy if flying indoors with intermittent GPS.
You say yourself that you got GPS warnings.
Fly outside to see if you get good GPS lock

 

[karlblessing]

If you're flying indoors, it's very very very common to have poor if not no GPS signal at all.

If the GPS count is 6 or less, and are not geographically spread out with poor signal, it can be very difficult to get a good fix on where you actually are.

DJI Drone's won't let you take off with less than 6 unless you choose to unlock it (along with acknowledging the risk in the dialog that follows). It'll rely more on the downward facing sensors provided there's enough light and good pattern it can detect off of.

 

[SkyeHigh]

Perfectly normal. GPS is not designed for indoor use. It requires an unobstructed ‘view’ of the satellites. You may get an occasional weak signal indoors but you should never rely on it.

Without a valid GPS lock it is also normal for your aircraft to drift. It goes into Attitude mode that is designed only to keep the aircraft stable and will easily drift in the wind.

 

[Deleted member 103366]

I have been in mid Atlantic according to the GPS of some of my indoor flights, I might even have got to the Middle East, ignore it.

 

[Meta4]

The issue is most likely with the Air Data as there will be updates from them as they work on there profiles.

The issue is not with Airdata.
It's completely normal to have faulty GPS data when most sats are blocked by a roof or other obstacles

you only need 3 to fly in the home .
Here is the Phantom 4 flying with 3 Sats.

This makes no sense.
You can fly with no sats.
But you need a minimum of 6 sats to fly with GPS position holding ability.
With three sats, you may as well have been flying with zero because you won't have horizontal position holding.

 

[Garatshay]

The issue is not with Airdata.
It's completely normal to have faulty GPS data when most sats are blocked by a roof or other obstacles



This makes no sense.
You can fly with no sats.
But you need a minimum of 6 sats to fly with GPS position holding ability.
With three sats, you may as well have been flying with zero because you won't have horizontal position holding.

Indoor flying should not rely on GPS, ever. As many have already observed, the service is not intended to operate indoors at all. However, DJI drones have optical sensing features that allow them to maintain a position without GPS - maybe not quite as reliably - but certainly effective indoors (unless there are no patterns or visible differences in the area...)

 

[SkyeHigh]

Indoor flying should not rely on GPS, ever. As many have already observed, the service is not intended to operate indoors at all. However, DJI drones have optical sensing features that allow them to maintain a position without GPS - maybe not quite as reliably - but certainly effective indoors (unless there are no patterns or visible differences in the area...)

Optical assistance can only help maintain height not horizontal position and then only upto approximately 30ft. The sideways pointing sensors are for collision prevention. The IMU’s micro mechanical (MEMS) sensors detect motion in the 3-axis and are used to keep the aircraft level but without GPS lock it will drift.

 

[Phantomrain.org]

The issue is not with Airdata.
It's completely normal to have faulty GPS data when most sats are blocked by a roof or other obstacles



This makes no sense.
You can fly with no sats.
But you need a minimum of 6 sats to fly with GPS position holding ability.
With three sats, you may as well have been flying with zero because you won't have horizontal position holding.

I was under the impression that it was 3 for a ground fix and 4 to get altitude and the Magic Number for the Mavic was 7 Sats to recognize and operate in P mode with GPS lock.
But the Phantom 4 might have fluctuated to 4 sats.

 

[EyesWideShut]

Optical assistance can only help maintain height not horizontal position and then only upto approximately 30ft. The sideways pointing sensors are for collision prevention. The IMU’s micro mechanical (MEMS) sensors detect motion in the 3-axis and are used to keep the aircraft level but without GPS lock it will drift.

@SkyeHigh, the optical sensors in the Mini 2's VPS are there to maintain horizontal position. When indoors try hovering over a small mat and pull the mat, the mini1/2 will move with as it thinks the wind has made the drone drift and will correct it's position to stay over the mat.

Here's the page on Visual Positioning from the Mini 2 User Guide, the Mini 1 is the same
.

 

[Jeff.K]

You might want to study up on GPS and potential issues it can be subject to such as Multipath interference. As long as you're flying with a clear unobstructed view of the sky it works great. However, wIth objects like our drones you can be indoors, or in urban or mountain canyons where you have trouble getting reception. Just loosing signal can be problematic, but getting multipath signals can result in erroneous position calculations which can cause all sorts of problems with a drone that navigates itself based largely on GPS data

 

[Meta4]

I was under the impression that it was 3 for a ground fix and 4 to get altitude and the Magic Number for the Mavic was 7 Sats to recognize and operate in P mode with GPS lock.
But the Phantom 4 might have fluctuated to 4 sats.

None of that is correct.
A handheld GPS unit will give an unreliable approximate fix with three satellites and requires a minimum of four for a reliable location data.
DJI won't allow their any of their drones to enter P-GPS mode with less than 6 sats, to give an extra safety margin.