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Reasons why the heading is not stable or incorrect

There can be several reasons for unstable or incorrect heading:

      1. You are using a MTi-3, MTi-30 or MTi-300 and you have set the filter profile to VRU_General. This filter profile does not have North referenced heading. You can use one of the following:
        • Enable Active Heading Stabilization (AHS)
        • Use Gyro Bias Estimation (No Rotation Update)

      2. You are using a MTi-2, MTi-20 or MTi-200 without Active Heading Stabilization (AHS). The heading of these units is not stabilized by default (no north reference). You can use one of the following:
        • Enable Active Heading Stabilization (AHS)
        • Use Gyro Bias Estimation (No Rotation Update)

      3. You haven't performed a magnetic calibration aka Magnetic Field Mapping (MFM). Please perform a MFM. How to perform a correct MFM is described in our Magnetic Field Mapper Documentation.

      4. You have previously performed a Magnetic Field Mapping (MFM). If you have performed a MFM in a certain environment and you take the Motion Tracker away from this environment, the MFM becomes invalid. This may cause inaccurate orientation readings. Please perform another MFM in the new environment. For more information also see the Magnetic Field Mapper Documentation.

      5. The magnetic environment is not homogeneous. The magnetometer requires a homogeneous magnetic field to reach the accuracy in the datasheet (under static and dynamic conditions). Especially when using the magnetometer as a reference (e.g. filter profiles GeneralMag on the MTi-G-710 and General in the MTi-3, MTi-30, MTi-300), a deviation in the magnetic field will mean a deviation in the heading. Please refer to the Magnetic Field Mapper Documentation and the MTi User Manual for more information about the influence of magnetic materials and magnets. 

      6. The MTi-3, MTi-30 and MTi-300 constantly adapt to the local magnetic field. Adopting the new magnetic field may even occur tens of seconds after the magnetic field has changed. This is intended behavior of the Motion Tracker to prevent short lasting magnetic distortions influencing the heading.

      7. You are using a MTi-G 7x0 and the heading observability is too low. This can occur when
        • You are driving or flying in a straight line
        • You are not moving
        • The GPS reception is lost

      8. It can also be that the gyroscope biases are too high. Distinguishing the gyroscope bias from the magnetic field variation is possible only when the bias is small enough, or when the magnetic field distortion is large enough. For example, a magnetic disturbance of a battery suddenly introduced will cause the magnetic field change so much that this is easily recognized as a magnetic distortion.
        However, sometimes the magnetic field is stable but the bias of the gyroscope is much higher. Adapting the high gyro bias value could make the orientation unstable, especially since such a high gyro bias estimate could also come from a gradually changing magnetic field. Not adapting the gyro bias causes a drift in the heading. The MTi 1-series in particular has a gyro that is lower-cost and (therefore) also has a higher turn-on-to-turn-on bias. Performing a SetNoRotation (Gyro Bias Estimation) procedure at the start of the measurement can solve this, as the gyro bias will be low enough to continuously estimate it during the measurement. 

 

For more information on the origin of drift also see: Understanding Sensor Bias (offset)

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