14 sats but not enough to get home point?

[Buel]

Hi all.

I just tried to fly and could see that it said I had 14 satellites but the icon was red and wouldn't let me get my home point and resttricted height etc. If I flew up to max height and stayed a minute then it would gain enough sats to fly, but then I would come down to 4 m and it would lose them again.

This is at my home where I have always enjoyed lots of sats and no issue previously.

Any ideas, please?

 

[mavic3usa]

My understanding is there's more to GPS and location than just "getting" satellites. I would do some basic research on consumer-grade GPS, how they get a fix, the quality of the signal, etc and go from there. Behinds the scenes, there's really a lot going on there....

 

[Phantomrain.org]

Nothing Wrong with flying up to get signal, you will be fine when you come back as you most likely will not loose signal as its harder to loose than gain.

Phantomrain.org
Gear to fly your drone in the Rain, Land on the Water.

 

[slup]

...I had 14 satellites but the icon was red and wouldn't let me get my home point

Good positional data aren't just dependent on the number of locked satellites... in the logs you also find something that DJI calls GPSLevel (or Navhealth), it's a kind of confidence computation that tells the flight controller if it can trust the positional data or not.

The GPSLevel have values from 0 up to the best 5. The HP isn't recorded until it comes up to a 4 for instance. If the GPSLevel is low you may see messages about GPS and/or Compass signal weak... & if reaching 0 you will have a switch to ATTI mode.

Exactly what's included in the GPSLevel isn't fully clear, but it involves GPS DOP & the compass.

Below an example from another flight... 27 satellites locked, 0 in GPSLevel .... & therefore that drone was in ATTI mode.

(Click on the chart to make it larger)

 

[Buel]

This is both fascinating and annoying
Thank you for this. The thing that confuses me is that is super normally? Perhaps agreeing to download the new software update and some calibration may help?

 

[Meta4]

This is both fascinating and annoying
Thank you for this. The thing that confuses me is that is super normally?

That's uncommon, but not unusual.
The time taken and number of sats before you have full GPS quality is quite variable and affected by a number of different factors.
I have seen it take >20 sats before being able to record a home point on occasion.

The sats are orbiting the earth while the earth rotates inside the "cage" their paths trace in space.
Which sats are visible in your sky and how many is changing all the time.
The number of sats acquired is only one factor.
Their spread across the sky is also important.
If they are all bunched in one part of the sky or in a line, you won't have suitable geometry to provide the required spread of sats.
Perhaps you just encountered an unusual random bunching of sats?
Does your launch point have a clear, unobstructed all-round skyview or is part of the drone's skyview blocked by buildings, terrain or tree cover?

Perhaps agreeing to download the new software update and some calibration may help?

No .. that won't make any difference to GPS sat acquisition times.
How long since you last flew is another factor that will affect sat acquisition times.

Time to first fix - Wikipedia

en.wikipedia.org

 

[Buel]

part of the drone's skyview blocked by buildings, terrain or tree cover?
Great question - yes it is

How long since you last flew is another factor that will affect sat acquisition times.
Interestingly, only a week but two months before that!

 

[Meta4]

part of the drone's skyview blocked by buildings, terrain or tree cover?
Great question - yes it is

This is a major factor.
The number of sats your drone can see is roughly proportional to the percentage of the sky it sees.
And more than the number of sats, it also means that the sats your drone does see, are more likely to be bunched and not giving the wide spread that's needed for good GPS location data.
Launch from somewhere that the drone can see the full skyview and things will be different for you.