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In-run Compass Calibration (ICC) and Representative Motion

Disclaimer: ICC in MT Software Suite 4.7 is the first released version and will undergo changes in the future. For the MTi-G-710, ICC is released as a beta. Some details about the implementation, among others on interface and algorithm, will be improved. 

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In-run Compass Calibration is a way to calibrate for magnetic distortions present in the sensor operation environment using an onboard algorithm leaving out the need for a host processor like a PC. It estimates the hard- and soft-iron effects and provides new magnetometer calibration parameters. 

Although it is a powerful mechanism, ICC only estimates distortions that are caused by objects that move with the MTi. External distortions from tables, structures, other vehicles etc will compromise ICC results. 

ICC will estimate the distortions in the envelope of motion: so when roll and pitch values during the ICC-procedure do not exceed e.g. 30 deg, the new magnetometer calibration parameters will only be valid up to 30 deg roll and pitch. When ICC is running in the background, it continuously evaluates, compensates and adapts calibration parameters with new information, e.g. dynamics. This implies that when the MTi reaches orientations that were not yet reached before, ICC will adapt and absorb the information in the envelope of calibrated orientations to get new estimates. 

Representative Motion

To expedite the estimation of magnetometer calibration parameters, there is a Representative Motion feature. Representative Motion is available in MT Manager, XDA and Low-Level Communication Protocol (Xbus protocol). Below are the results of an MTi 1-series attached to a battery. The magnetic field sometimes even clips, reaching ~2x times the normalized magnetic field (remember that a constant value of 1.0 over the entire range means that the magnetometer is calibrated correctly for the environment). After the initial period of 13 seconds, Representation Motion is switched ON for ~25 seconds.  This is indicated with the status bit flag. Once the results are written to the non-volatile memory, the magnetic field norm stays close to 1.0, showing a meaningful calibration done (for sensor-fixed distortions) for the use of the magnetometer sensor as a compass. 

Note that although MT Manager was used, this procedure fully takes place inside the MTi on the onboard processor during operation. As the ICC evaluated calibration parameters need to be stored in Config Mode, writing the results in the eMTS after Representative Motion mode (or ICC) is the only time that the the sensor fusion algorithm is interrupted: ICC itself is running unobtrusively in the background. 

Please refer to this article to find more information on how to use ICC and Representative Motion in MT SW Suite:

Using ICC Representative Motion (RepMo) in MT Software Suite.

Using ICC with AHS

When using ICC together with AHS, the sensor fusion algorithm first applies ICC and then applies AHS. Although AHS doesn't use the magnetic field as a reference, ICC may provide a different magnetometer reading estimate. This may have an effect on AHS. 

Using ICC with XDA processing

ICC and Representative Motion are designed to be used when the MTi is set to onboard processing. ICC can be enable when processed on a file, but it will only be possible to start Representative Motion when the MTi is set to onboard processing (i.e. orientation output is enabled in the output configuration). 

 

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