Understanding Mission Planner Auto Analysis (Compass)


I am trying to understand how much interference there is on my GPS+compass mounting location, so I did a few tests today to collect some data. I got a little confuse by the message in the mission planner auto analysis.

Test: Compass = WARN - Moderate change in mag_field (29.78%)
Max mag field length (648.90) > recommended (550.00)

Anyone know how mission planner auto analysis evaluate “change in mag_field” and “Max mag field length”. In the sensors/compass/compass vs throttle MavgraphsMP plot, I am seeing max magnetic field to be 542.82 instead of 649.9

Any insight in this would be appreciated. Thanks!

Auto Analysis is out of date and of little value.

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Thanks for the prompt reply. That’s good to know.

I’ve been reading that in order for loiter mode to work correctly, the change in mag field has to be lower than 30%. My setup is at 29.78% based on the auto analysis, but since it is out of date, how can I evaluate the change in mag field percentage?

Is it just the difference between the min and max value of the magnetic field?

Read through the compass interference section here.
If youre using plot.ardupilot.org to view logs, there’s a compass preset that will plot the mag field length for you. Likewish with mission planner, on the bottom theres a dropdown with selectable presets.

See compassmot calibration


Or here (best option):

Note: Page down to the MAVExplorer’s utility instructional video.

Thanks for the information guys! I will give compassmot a try and figure out the % of interference from there. I am just curious if anyone knows how the mission planner calculates the % interference (just for personal understanding)

This only has meaning if you believe Auto Analysis has meaning. It’s referenced to a value (a percentage of) that has no real relevancy. Sqr root of the sum of the squares to a value that might have meant something in the Wayback machine.

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