Hello, recently I found out that the greatest precision of measuring an altitude of DJI Spark is in meters with 0.1 precision, but I would like to measure in centimeters. I want to be able to measure at least from 5 to 10 centimeters above the ground. Is that possible? I found out we can calculate altitude from IMU sensor, but would that be working correctly even If data were filtered to compensate for noise or is there maybe a better solution withotu using IMU data?

Thank you for help.

0.1m is the resolution comming from the firmware. Unless you hack the firmware you can't get better than that.
Imu? good luck with that, The drift would be insane. The only way to read the imu is through parameters, and I think it's limited to 10Hz if you don't do it on the drone, which again need hacking.
I would opt for some kind of CV, if you need that precision.