how accurate is the gps on mavic??

[genesimmons]

hi all very new piolot here, only flown 3 times, i noticed the altitude on the app shows in the negative when i get close to land, is that normal and i get the warning find a better place to land even though i took off from there and its my rth point, gps doesant seem very accurate but has full bars

 

[BD0G]

(95% of the time or better) can get 3 meter accuracy with GPS as stated by the US Government.
That is the GPS accuracy in general. 3 meters = 9.8452 feet.

 

[sar104]

hi all very new piolot here, only flown 3 times, i noticed the altitude on the app shows in the negative when i get close to land, is that normal and i get the warning find a better place to land even though i took off from there and its my rth point, gps doesant seem very accurate but has full bars

When you say that the GPS doesn't seem to be accurate, are you still referring to the altitude reading? If so, the altitude is not determined from GPS data, it is derived from the internal barometric sensor. That should be quite accurate but may drift over the duration of a flight due to changes in atmospheric pressure.

 

[Costa Rica Guy]

My understanding is that where you take off from is ground zero. I am at the beach, but uphill about 150 feet. When I take off from my deck the altitude reads ....for example...8 feet, but as soon as I fly down towards the beach and pass below my deck level, the altitude is in negative numbers

 

[genesimmons]

ahh thanx for the replies, yes i assumed altitude was done by gps, my rth point was negative nmbers so i thought thats why it gave me warning, didnt seem accurate that when i take off its positive but land its negative

 

[locoman]

it must be pretty accurate since the RTH mode puts my bird within a few inches of where it takes off from.

 

[locoman]

My understanding is that where you take off from is ground zero. I am at the beach, but uphill about 150 feet. When I take off from my deck the altitude reads ....for example...8 feet, but as soon as I fly down towards the beach and pass below my deck level, the altitude is in negative numbers

That is as it should be, since you are flying below your take off elevation.

 

[owner]

As the US Government sits on a SA-button (selective availibility), they can do a time-correction to the sattelites above to decrease the accuracy of the GPS-reciever. This is to have a step ahed in case of war and GPS-controlled missiles.

However, the Mavic supports GLONASS, wich is a Russian GPS-system wich dont have this time-correction. The Russians use higher inclination on their sattelites, so they achieve higher coverage on the latitude of the earth.

 

[HiKen51]

My understanding is that where you take off from is ground zero. I am at the beach, but uphill about 150 feet. When I take off from my deck the altitude reads ....for example...8 feet, but as soon as I fly down towards the beach and pass below my deck level, the altitude is in negative numbers

I just noticed that the GPS coordinates on a photo shot on a recent brief flight registered 76.9 m below sea level. I noticed this when checking coordinates in Adobe Bridge. But while I was flying, I believe the altitude above home point probably was accurate. Not sure why the gps altitude reading would be so far off. Photos I shot this AM seem to be about right.

 

[SYC12]

it must be pretty accurate since the RTH mode puts my bird within a few inches of where it takes off from.

This ONLY possible with the aid of photo taken 30' above the home point.
You can observe that during RTH, MP would fly back to presumably Home Point first based on recorded GPS and hover at preset attitude. At that point, you would realize MP is not directly above the HP and typically would be off by about 10'. Then MP would compare current HP photo with recorded HP photo and move to directly above the HP.......

In OP case, I think OP didn't give MP a chance to take a photo or didn't take off vertically then hover directly above HP few seconds, otherwise RTH landing position should be within inches as you stated.

 

[SeaComms]

I just noticed that the GPS coordinates on a photo shot on a recent brief flight registered 76.9 m below sea level. I noticed this when checking coordinates in Adobe Bridge. But while I was flying, I believe the altitude above home point probably was accurate. Not sure why the gps altitude reading would be so far off. Photos I shot this AM seem to be about right.

The GPS coordinates do not calculate height above sea level, only the latitude and longitude. The barometric sensor also does not register height above sea level, only the height above the takeoff point and I don't believe the altitude is stamped in the header for the photos.

 

[Keule]

I don't believe the altitude is stamped in the header for the photos.

Here an EXIF excerpt of an image:
..
GPS Version ID : 2.3.0.0
GPS Latitude Ref : North
GPS Longitude Ref : East
GPS Altitude Ref : Above Sea Level
..
Absolute Altitude : +447.73
Relative Altitude : +50.40
..
GPS Altitude : 50.4 m Above Sea Level
GPS Latitude : 48 deg 17' 45.82" N
GPS Longitude : 11 deg 50' 30.93" E
GPS Position : 48 deg 17' 45.82" N, 11 deg 50' 30.93" E
..

 

[genesimmons]

This ONLY possible with the aid of photo taken 30' above the home point.
You can observe that during RTH, MP would fly back to presumably Home Point first based on recorded GPS and hover at preset attitude. At that point, you would realize MP is not directly above the HP and typically would be off by about 10'. Then MP would compare current HP photo with recorded HP photo and move to directly above the HP.......

In OP case, I think OP didn't give MP a chance to take a photo or didn't take off vertically then hover directly above HP few seconds, otherwise RTH landing position should be within inches as you stated.

this is very intersting i did not know this, thanx for sharing, i have since done many rth and i do notice it hover but didnt realize it may be adjusting from a photo, very intersting

 

[SeaComms]

Here an EXIF excerpt of an image:
..
GPS Version ID : 2.3.0.0
GPS Latitude Ref : North
GPS Longitude Ref : East
GPS Altitude Ref : Above Sea Level
..
Absolute Altitude : +447.73
Relative Altitude : +50.40
..
GPS Altitude : 50.4 m Above Sea Level
GPS Latitude : 48 deg 17' 45.82" N
GPS Longitude : 11 deg 50' 30.93" E
GPS Position : 48 deg 17' 45.82" N, 11 deg 50' 30.93" E
..

Wow. Well I'll be stuffed! Never seen that before. It knows height above sea level, go figure... Should be able to tell height above ground level then and let you fly up the side of a mountain!

 

[sar104]

Wow. Well I'll be stuffed! Never seen that before. It knows height above sea level, go figure... Should be able to tell height above ground level then and let you fly up the side of a mountain!

Knowing altitude above MSL still doesn't tell it altitude AGL unless it has a stored digital elevation model. And if it had a DEM it could calculate AGL based on takeoff location anyway - it would not need GPS altitude above MSL.

 

[skan]

It's a pity they just used the L1 signal for something so important as positioning the drone.
The phone Xiaomi Mi 8 uses both L1 and L5 and gets an accuracy of 30cm, and it adds not only Glonass but also Beidou.