Hello, I'm having problems with the altitude not being reported properly in DJI Go 4 and my new Phantom 4. Sometimes under reporting and sometimes over reporting. Like being negative at landing or way positive at landing. I'm afraid to do much like waypoints if I can't trust the altitude. Please help.
Thanks in advance.

The altitude in a Phantom is measured by a barometer chip, it is subject to variations according to air pressure and temperature. There is nothing much you can do about it. If you are flying waypoints, just be ready to adjust the aircraft if it is not flying at the correct altitude.

How big are the differences you observe?

Bullflyer Posted at 2017-5-13 07:12
How big are the differences you observe?

15 to 25 feet. The VPS is working fine. It reports properly up to 30 feet.  Today I was hovering inches above the ground and and "H" was giving me 23 feet. Sometimes at landing it tell me negative 15 feet. I hope I don't have to send it back. IMU and compass have been calibrated and are reporting in good health.

ocean224 Posted at 2017-5-13 09:26
15 to 25 feet. The VPS is working fine. It reports properly up to 30 feet.  Today I was hovering inches above the ground and and "H" was giving me 23 feet. Sometimes at landing it tell me negative 15 feet. I hope I don't have to send it back. IMU and compass have been calibrated and are reporting in good health.

And this happens every time you lift off the P4, or just occasionally ?

Bullflyer Posted at 2017-5-13 12:42
And this happens every time you lift off the P4, or just occasionally ?

Every-time I lift off. I have tested with two devices Iphone 6 and ipad air2.

I would reinstall the FW using the DJI assistant, replace the SD card (first) and then do IMU calibrations. I had one that was REALLY far off, and I fixed it that way.

droneflyers.com Posted at 2017-5-13 15:00
I would reinstall the FW using the DJI assistant, replace the SD card (first) and then do IMU calibrations. I had one that was REALLY far off, and I fixed it that way.

Please. The SD card has nothing to do with this issue.

Geebax Posted at 2017-5-13 15:36
Please. The SD card has nothing to do with this issue.

OK, what about the rest of his reply?
Thank you.

droneflyers.com Posted at 2017-5-13 15:00
I would reinstall the FW using the DJI assistant, replace the SD card (first) and then do IMU calibrations. I had one that was REALLY far off, and I fixed it that way.

What exactly do you mean by "replace the SD card (first)"?
Thank you.

I've seen it differ by 16 meters at times.  Landing is rarely Take off = Zero meters, and Landing = Zero meters.  The Autopilot autonomous app running on iOS allows one to tighten the deviation from their default in their app of 16 meters down to I think it was 6 meters, not great but at least something.  They also suggest doing a pre-flight to verify and then final tune off it for waypoints where proximity may be a concern.   Don't know what DJI tolerance is in GO 4 but it might be 16 meters too.

More odd is on an outward flying leg it may be correct, but coming back it climbs in altitude by maybe 5 meters or so visibly while GO reports the same altitude as the original even though once landing GO will not be Zero meters as it should.  Then it goes out again at the original altitude so it seems direction as well, which may explain some of the odd gimbal horizons when yawing still photos around a 360 degree panorama.

I think their software needs some better tuning, and maybe use more of the on-board sensors in altitude as well for correct landing numbers.  Could be electronic thermal drift too as the unit heats up in flight and later normalizes.

I place no value in the altitude function, let alone any of the other sensors. Fly the bird as if you are in it. LOS.  If I fly a Litchi flight I fly at LOW speed first then fly at what speed I want for that filming. CAUTION is the word. Remember, multiple takes are allowed.