I went for a fly today, and by the time I landed the drone, in the same location, my drone said that it was 9.1 meters lower. Has anyone else had this issue?

Lower than what?
Your home point/take off point is always zero altitude. Did ist say upon landing -9.1 meters?

Yes, upon landing, the drone said “-9.1m”

Hi,

height indication is derived from a barometric sensor. If this sensor works 100% accurate and no pressure changes than it should read 0 height at landing.

But 100% accurate is not feasible so some height fluctuations readings at landing is normal.
If the actual air pressure is changed (happens at weather changes) 'mis-readings' shows higher values.

Fluctuations will increase if during a flight you fly higher just low level flights.

VPS height is accurate at lower height, so check the next flights and you will notice that it will always fluctuate a little.
cheers
JJB

UNsyncED Posted at 2018-10-1 00:04
Yes, upon landing, the drone said “-9.1m”

One tip:
Reply to somones post rather than posting underneath.
This way the poster receives a message about your reply without having to re-visit the thread.

I guess the Mavics determine altitude the same way as the Phantoms.
And since the Phantom 3 series altitude is determined by GPS.
Not by barometer.

GPS is very bad for altitude determination. It can easily be off by 50m or more.
So 9m is not bad ;-)

Altitude is not determined by GPS.

It's the drones internal barometer gauged against the altitude from the home point where the drone initially took off.

A CW Posted at 2018-10-1 01:09
It's the drones internal barometer gauged against the altitude from the home point where the drone initially took off.

I’m surprised that the atmospheric pressure can change so quickly in a 17 minute duration.

Yes, the drone landed at the same location as launching (within 5 meters, with no change in altitude)

UNsyncED Posted at 2018-10-1 01:30
I’m surprised that the atmospheric pressure can change so quickly in a 17 minute duration.

Yes, the drone landed at the same location as launching (within 5 meters, with no change in altitude)

Strange - try calibrating the IMU on a level surface and see if that impacts on the reading

Hi. Thank you for reaching DJI Forum. Did you land the drone lower than the Homepoint?

A CW Posted at 2018-10-1 01:09
It's the drones internal barometer gauged against the altitude from the home point where the drone initially took off.

Can you reference us to some DJI doumentation which says it's determined by barometer?

UNsyncED Posted at 2018-10-1 01:30
I’m surprised that the atmospheric pressure can change so quickly in a 17 minute duration.

Yes, the drone landed at the same location as launching (within 5 meters, with no change in altitude)

An explanation would be that DJI uses the same sytem like with the Phantoms: GPS

Read post #2 on this thread:
https://forum.dji.com/thread-148221-1-1.html

This one is also interesting:
https://forum.dji.com/thread-154027-1-1.html

Eric13 Posted at 2018-10-1 03:49
Can you reference us to some DJI doumentation which says it's determined by barometer?

Here are some tips for you
https://phantompilots.com/thread ... or-barometer.51568/
Can you also explain how altitiude readings are still relatively accurate during flight when GPS/GLONASS is lost? Is that because the drone uses only it's barometer to assess altitude?  

I see 0 altitude values on takeoff and negative values on landing in the same spot all the time on my M2P. Never noticed this on Mavic Air logs.
00m 39.3s Assisted Takeoff 0ft
21m 05.4s Confirm Landing -11.2ft

A CW Posted at 2018-10-1 06:48
Here are some tips for you
https://phantompilots.com/thread ... or-barometer.51568/
Can you also explain how altitiude readings are still relatively accurate during flight when GPS/GLONASS is lost? Is that because the drone uses only it's barometer to assess altitude?

Thanks.
I did some more reading in other threads and see where I am mistaken.
The Phantoms (not sure about Mavic) show in exif data the GPS reading for altitude.

That made me assume that the altitude reading /altitude displayed on screen is taken from GPS as well.
That is apparently not the case.
Strange tough that GPS altitude is in exif...

DJI Wanda Posted at 2018-10-1 03:00
Hi. Thank you for reaching DJI Forum. Did you land the drone lower than the Homepoint?

Hi Wanda, The drone landed at the same altitude as the launching site, about 5m away. I have the flight log if this helps.

Eric13 Posted at 2018-10-1 10:39
Thanks.
I did some more reading in other threads and see where I am mistaken.
The Phantoms (not sure about Mavic) show in exif data the GPS reading for altitude.

It's an age old debate

UNsyncED Posted at 2018-10-1 14:15
Hi Wanda, The drone landed at the same altitude as the launching site, about 5m away. I have the flight log if this helps.

Did you try to calibrate the IMU and compass?

To add a few elements to this conversation, I also noticed 2 days ago the same problem when I was about to land, and the height of the drone was negative (note: I prefer to use height in this context, as it is the height from the ground, called AGL, rather than altitude, that is more generally used  for the height above sea level, called ASL). It is the first time that this happens to me, but it was also the first time that I climbed at a height of 150 meters (yes, it is allowed where I was flying). So maybe there is some inaccuracy in the measurement, that cumulates if you are climbing high?

For me, it is an evidence that the drones are using a barometer for measuring the height, as the precision of the GPS would never allow it to hover without climbing nor descending as it does.

Concerning the EXIF data, in my case there is an altitude displayed, and it appears to be not the altitude of the drone, but the altitude of the ground at the X, Y GPS coordinates. But maybe Lightroom has overriden this data when doing location lookup.

pjollain Posted at 2018-10-1 23:55
To add a few elements to this conversation, I also noticed 2 days ago the same problem when I was about to land, and the height of the drone was negative (note: I prefer to use height in this context, as it is the height from the ground, called AGL, rather than altitude, that is more generally used  for the height above sea level, called ASL). It is the first time that this happens to me, but it was also the first time that I climbed at a height of 150 meters (yes, it is allowed where I was flying). So maybe there is some inaccuracy in the measurement, that cumulates if you are climbing high?

For me, it is an evidence that the drones are using a barometer for measuring the height, as the precision of the GPS would never allow it to hover without climbing nor descending as it does.

hmm.. I agree that it shouldn't be called “altitude”, but in DJI GO 4 it does list it as "Max Alt.", so therefore I'd prefer to use a consistant language which everyone understands.  From an engineering perspective, I'd prefer to call it Delta Altitude (ΔAlt. for short), but I do like your acronym of AGL.  The only problem with AGL is the ground level is constantly changing ;-).
I'll try calibrating my M2P as Wanda suggested, and will let everyone know of the results.

I've had the same problem with the negative altitude. I was doing a low level point of interest around a tree at the minimum of 3 metres. Had to keep landing and rebooting the drone to reset the altitude to 0, really annoying as there wasn't anywhere lower that I could take off from.

well it really can be a big problem... I am noticing it also now... but not in the beginning when I started using the DJI Mavic 2 Pro... problem is, that when you try a RTH it flies up to 30 meters... but... as I notid yesterday that is 30 meters PLUS the difference... so mine flew up about 50 meters... Do we have faulty barometers or has there been a solution I overlooked?
Yesterday evening I refreshed the firmware of my remote control and my DJI Mavic 2 and did the IMU thing...
I'm going to test fly this afternoon...

Take care...

CanonMax Posted at 3-29 01:10
well it really can be a big problem... I am noticing it also now... but not in the beginning when I started using the DJI Mavic 2 Pro... problem is, that when you try a RTH it flies up to 30 meters... but... as I notid yesterday that is 30 meters PLUS the difference... so mine flew up about 50 meters... Do we have faulty barometers or has there been a solution I overlooked?
Yesterday evening I refreshed the firmware of my remote control and my DJI Mavic 2 and did the IMU thing...
I'm going to test fly this afternoon...

I’ll keep an eye on it.  I haven’t flown for a little while, waiting on my goggles to be repaired.

Same here with M2E.........I was -53 ft landing in exact same spot I took off from just 10 minutes earlier (see picture below). I then Rebooted the AC, double checked take off height was zero'd,  took off, flew for 5 minutes and came back at like -21 ft this time!!

Sorta crappy esp if one wants to use this height  measurement for telemetry.  Think my M2Z is doing this too.........Is there a fix for this?

.

Droning 24/7 Posted at 4-7 20:19
Same here with M2E.........I was -53 ft landing in exact same spot I took off from just 10 minutes earlier (see picture below). I then Rebooted the AC, double checked take off height was zero'd,  took off, flew for 5 minutes and came back at like -21 ft this time!!

Sorta crappy esp if one wants to use this height  measurement for telemetry.  Think my M2Z is doing this too.........Is there a fix for this?

You should ask @DJI Wanda, as she has participated in this thread. I hope that she can help you, especially if you want to use the M2E (emphasis on ENTERPRISE) for telemetry.

DJI Wanda Posted at 2018-10-1 23:26
Did you try to calibrate the IMU and compass?

Is there a fix for this? Please read above thread
@DJI Wanda ?

I have this issue with my Mavic Pro, but so far only at the flying field.....flying around my house no issues. I am new to DJI, only about ten flights on my Pro, so I am staying close while I adjust to the controls and settings. I find it a bit unsettling to watch it climb and descend in a hover while the home elevation keeps changing. I have seen from +35 to -18 in less than a minute. My own personal built drones don't have Barometers, I just use GPS for Return To Home, so this is a new experience for me. I will try the IMU calibration at the field, neither calibrating the compass, nor resetting the home point in the APP made any difference.

Bigdog714 Posted at 4-9 12:43
I have this issue with my Mavic Pro, but so far only at the flying field.....flying around my house no issues. I am new to DJI, only about ten flights on my Pro, so I am staying close while I adjust to the controls and settings. I find it a bit unsettling to watch it climb and descend in a hover while the home elevation keeps changing. I have seen from +35 to -18 in less than a minute. My own personal built drones don't have Barometers, I just use GPS for Return To Home, so this is a new experience for me. I will try the IMU calibration at the field, neither calibrating the compass, nor resetting the home point in the APP made any difference.

Same........ Cal'd everything more than once, re-loaded SW, nothing fixes this issue, DJI isn't saying anything on this....... Think the sensor/barometer is bad! Else if it were FW, thinking everyone more or less would be having this issue. Sending mine in for a fix (3 fixes actually), will report back when I get it back

Streetmagus Posted at 2018-10-1 00:57
Altitude is not determined by GPS.

Actually, GPS does allow calculation of altitude once you have more than 4-6 satellites. but barometric data is slightly more accurate.
I'm unsure if the Mavic readout uses data from both GPS + the barometer, but altitude via GPS is common in most hiking watches.   

http://gpsinformation.net/main/altitude.htm

Cheers
Ian

I got answer on another forum. Answer is following:

DJI Drones use an air pressure Altimeter. Every time you start your drone it is zeroed and is very sensitive to pressure so every foot of height will change the pressure on the Altimeter. This is a realitivly accurate way to measure altitude and more accurate than civil GPS 3D height.
Mavics also, under 30 feet use (Mavic1 ultrasonic) Mavic2 infra red to montitor height about ground and hold its position. Once above 30feet then it switches to GPS for position hold. If your Drone is not holding a stable height below 30 feet and moving up and down then you have a problem with your IR sensors.

Please check my picture below. H showing - 5.9m, but VPS sensor showing correct altitude of 0.8m.

Usually this misreading happens during high wind. When flying below 30 feet always go by the red VPS reading right on bottom, slight right of your Go4 screen.

Droning 24/7 Posted at 4-7 20:19
Same here with M2E.........I was -53 ft landing in exact same spot I took off from just 10 minutes earlier (see picture below). I then Rebooted the AC, double checked take off height was zero'd,  took off, flew for 5 minutes and came back at like -21 ft this time!!

Sorta crappy esp if one wants to use this height  measurement for telemetry.  Think my M2Z is doing this too.........Is there a fix for this?

It’s solved. Please see my post at the bottom

Droning 24/7 Posted at 4-7 20:19
Same here with M2E.........I was -53 ft landing in exact same spot I took off from just 10 minutes earlier (see picture below). I then Rebooted the AC, double checked take off height was zero'd,  took off, flew for 5 minutes and came back at like -21 ft this time!!

Sorta crappy esp if one wants to use this height  measurement for telemetry.  Think my M2Z is doing this too.........Is there a fix for this?

It’s,solved. Please see my post on the bottom.