Height change when relative flying

Height change 6-8 meters when flying . what can I do for 1-2 meters altitude accuracy ?

Pixhawk 2.1 . Quadcopter .

I need a log. Without one, I can only speculate.

My first ideea is that the mission was flown with heading-hold, and there’s a particularity about your frame regarding airflow and hence pressure around the FC, making them different in forward vs. backward flying.

I made windproof around pixhawk cube and I had precision of 2-2.5 mt.

So there’s improvement. Now - I’m still without a log, so can only speculate - load any 4.0 firmware and do a FFT analysis hover. Your AccZ and VibeZ also affect your FCs altitude estimations.

log: https://drive.google.com/open?id=1h9YaCpNplOQ5CNeXp55b_EX5RL6HUyED

Very fast looking at the log. For the entire flight, your CCW motors are pushed way harder then the CW ones. There’s a motor+prop misalignment that’s pushing your frame in CCW direction.

Then, looking at barometer reporting vs GPS altitude, I see that forward flight versus backward flight discrepancy:

Also, your VibeZ, while being acceptable, it spikes at times, even leading to a pair of clipping events.

I’d address the motor imbalance first, then, like I said above, do a short FFT hover and vibration analysis for a notch filter.