Compass turning

I am wondering why cellphone and car navigation does not need turning compass when using GPS navigation.
Because it is not easy job to turning compass if the vehicle move to different city.

You don’t need to re-calibrate the compass when you move to a different city (or Country). I don’t know why this misinformation persists. Ardupilot has a feature called auto declination which compensates for this and is turned on be default. The only time you have to re-calibrate the compass is if there is a hardware change on the vehicle.

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I’ve added a tip to the compass calibration wiki page to specifically mention that recalibration is not required when you move locatdions. This should appear in the next 10min or so.

By the way cellphone and car navigation systems (i.e. maps showing you where you are and how to get to the destination) don’t require the same level of accuracy because they’re not in control. If the heading is off by 45 degrees it may look odd to the user but it’s not dangerous.

By the way ArduPilot Rover and Plane (but not Copter) also correct the vehicle’s heading using the GPS. They can do this because they can assume the vehicle mostly moves in the direction it is facing. This feature is slightly tricky in Rover though because some rovers don’t move very quickly and so the GPS heading (the direction the vehicle is moving) can be very inaccurate. I have not (yet) looked too closely at how much the EKF is correcting the heading using the GPS. It’s possible we could improve this.

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