Hello.
I recently noticed that the altitude shown on DG4 is not realiable/correct. After take off the altitude seems ok, a couple of minutes later flying the drone (p4p)  I fly it back where I'm located and I set it at my head's height, I'm 1.72m, the drone shows 3.5m. I repeated the test with different batteries and it always is meassuring wrong altitude. I read that barometer can't be calibrated, so I don't know from where to attack this problem. The drone had acquired 20+ satellites. How can I further analyze and provide information? Of course I've got the flight logs, is it possible to extract data from them when a picture was taken? I could provide the altitude from the log and the picture taken (me) so I could compare heights.

thanks in advance.

The barometer chip  relies on pressure.
The barometer chip sits with the IMU.
With some of the new models (mavics/p4p's), DJI has suggested NOT to do IMU calibrations as they have accurately done it at Shenzen.
I find this wrong as DJI ships around the world to different locations, different altitudes, different weather conditions.
If you redo your IMU calibrations correctly, the barometer is more accurate and you have quicker IMU warm up times.
I do did mine (mavic) before my first flight and the baro is accurate. I dont have any warm up times (except if i'm at colder places like mountain tops/snow fields).

QuanthonyTrang Posted at 2017-6-13 15:22
The barometer chip  relies on pressure.
The barometer chip sits with the IMU.
With some of the new models (mavics/p4p's), DJI has suggested NOT to do IMU calibrations as they have accurately done it at Shenzen.

Unfortunately I flew today with regular conditions, around 18C so I can't blame the temperature. I rechecked the logs and the app was showing altitude 5m and it was way below that height.

bup Posted at 2017-6-13 17:55
Unfortunately I flew today with regular conditions, around 18C so I can't blame the temperature. I rechecked the logs and the app was showing altitude 5m and it was way below that height.

You are missing the point.
DJI "calibrated" your drone in CHINA. This means it has been sent with CHINA's climate parameters.
You need to calibrate your IMU in YOUR COUNTRY to give it the correct climate parameters.

QuanthonyTrang Posted at 2017-6-13 18:03
You are missing the point.
DJI "calibrated" your drone in CHINA. This means it has been sent with CHINA's climate parameters.
You need to calibrate your IMU in YOUR COUNTRY to give it the correct climate parameters.

I understood that, however I assumed it was done under lab conditions. Pressure, Altitude, Temperature.
If I do the IMU calibration right now, 7 levels above ground how would it affect the result? At least I should do it aorund sea level, don't I?

bup Posted at 2017-6-13 18:04
I understood that, however I assumed it was done under lab conditions. Pressure, Altitude, Temperature.
If I do the IMU calibration right now, 7 levels above ground how would it affect the result? At least I should do it aorund sea level, don't I?

How does DJI know exactly where you drone is going to be delivered?
Doesnt have to be done at sea level. It can be done in your room

Don't fly your drone for and hour or so to make sure its cool. I do mine early hours of the morning and store it in a shady area. Make sure you youtube some P4P instructions as i dont own a P4 series. It could be different to the mavics. The mavic is done via the assistant 2 software and requires 5 rotations of the mavic.
Make sure you find a leveled surface free of any vibrations.
Remember to remove the gimbal lock.
If you are doing it indoors, then Ignore any magnetic interference warnings.
Make sure you do the IMU cailibration the drone immediately after powering it on. The longer you leave it on, the warmer the internals will be and the less accurate the calibration will be (in some cases it will fail due to heat).

Once done, redo the gimbal calibration (IMU speaks to the gimbal).

QuanthonyTrang Posted at 2017-6-13 18:19
How does DJI know exactly where you drone is going to be delivered?
Doesnt have to be done at sea level. It can be done in your room

Just finished both, I will try it this weekend or next week. Thanks for your advice.
Have you ever loss altitude while flying in S-MODE?

Like previously mentioned, give an IMU a shot and let us know if there are any changes.

bup Posted at 2017-6-13 18:37
Just finished both, I will try it this weekend or next week. Thanks for your advice.
Have you ever loss altitude while flying in S-MODE?

If S-mode = sports mode then yes.
Flying at a continuous straight line will lose altitude on quads without VPS.
Sports mode on the Mavic switches off the VPS and OA. The quad will lose a bit of altitude over a certain distant.

You have the P4P correct? It may be different as i recall the P4P has sensors active on sports mode and you shouldnt lose altitude. It is however possible that the area you are flying in may absorb sound or low lit and therefore the VPS may not work. Confirm this with the manual or DJI staff here.

QuanthonyTrang Posted at 2017-6-13 19:48
If S-mode = sports mode then yes.
Flying at a continuous straight line will lose altitude on quads without VPS.
Sports mode on the Mavic switches off the VPS and OA. The quad will lose a bit of altitude over a certain distant.

I finally was able to try the altitude problem again after IMU calibration and the problem persists. I attach a screenshot from DJI GO 4 app and the picture taken. It shows 2.7m H however could have been no more than 40-50 cm from the ground.

At least your VPS is correct at 0.5m

lannes Posted at 2017-8-25 13:23
At least your VPS is correct at 0.5m

Yes but that's if I'm near the ground. Flying at 100m or 200m I wouldn't be able to cross check it.

I flew yesterday again and the same error occurs. Hovering back from a mission at around 1.7m it shows 4m on the DJG4 app. I'm using a new phone and the remote control was re paired after the suggestion in post above. What can I do to keep getting data to fix it?

Try calibrating compass

fans61699a75 Posted at 2017-11-17 09:03
Try calibrating compass

The compass has no bearing on altitude measurements. The variation in altitude is normal for a barometric system. That's why the VPS takes over height measurement when close to the ground. And altitude is not measured by the GPS system either, or it would be woefully innacurate.

It is really not an issue, don't sweat it. Minute changes in air pressure can change the altitude reading when in flight.

Have you tried just letting the drone hover at say 1.2 mtrs for about 15 20 minutes and see if there is any change in altitude reading. I have a feeling your issue may be caused by internal components adjusting in value as they warm up.
This is no cause for real concern as you should be flying vlos anyway so the altitude reading shouldnt effect any flight capabilities.