On 2014-05-11, 11:28 AM, joerg Reisenweber wrote:
This all assumes a locked and defined mounting situation for the magnetometer.
Then yes. For an embedded device however this method tells you nothing about
the magnetometer heading. The embedded device can change relative orientation
to the vehicle that's driving.
PS: you must be very sure about the vehicle moving exactly straight ahead as
well, for anything but a non-sliding car that's not guaranteed, think boat,
even airplane

We're talking calibration here. Yes the unit should be rigidly mounted for calibration of the sensors. There are also periods of "stay still for X seconds" at various points in such a calibration. I have done and continue to do lots and lots of AHRS calibrations of various types on aircraft (airplanes and helicopters). I would be more than happy to share the information that I have on various calibration techniques.

Once the sensors are calibrated (i.e. figuring out the drift of the Rate Gyros when sitting still) and the magnetic environment of the device is known, what's left is the alignment procedure. Every time you start the AHRS code on the device, it would need to be motionless for a while. Lying the GTA02/GTA04 flat on a table for example for perhaps 2-3 minutes might be sufficient.

I feel that this likely the reason why even the latest mainstream phones don't have AHRS or IMU capability (an IMU would enable indoor navigation over only very short distances in a smartphone, given the rather crude quality of the MEMS sensors and horrific gyro drift expected if you are bouncing around with the smartphone in your hand and moving rather slowly without GPS aiding the Kalman filter).

Application for an AHRS on a smartphone would be for enhanced geo-referencing of photos and "Google Glass" type applications that don't make you look like a Glasshole. The other obvious application is as an emergency backup attitude (Pitch and Roll) and Heading indicator for airplanes and helicopters.... or simply recording of the sensor data and doing post-processing on a server to process the data later (think extreme sports, like playing back a skydive for example).


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