There can be several reasons for unstable or incorrect heading:
- 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:
- 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:
- 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.
- 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 may become 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.
- 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 MTi7 or 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.
- 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.
- You are using an MTi-7 or MTi-G 7x0 and the heading observability is too low. This can occur when
- the application is moving in a straight line
- the application is not moving or very slowly moving
- GNSS reception is lost
- It can also be that the gyroscope biases are too high. Distinguishing the gyroscope bias from the magnetic field disturbance is only possible when the change in magnetic field is significantly higher than the gyroscope offset. Performing a No Rotation Update at the start of the measurement can solve this, as the gyro bias will be low enough to continuously estimate it during the measurement.
- When using the magnetic field in the filter profile (e.g. filter profile GeneralMag), the magnetic field is used as a reference. This means that when the magnetometer is clipping, the magnetic field will not be used in the sensor fusion algorithm. When there is a desire to continue to use the magnetic field, place the MTi in another location where the magnetic field is less disturbed.
For more information on the origin of drift also see: Understanding Sensor Bias (offset)