Filter Kinematic Constraints
A selection of kinematic constraints is available that can improve Navigation Filter performance under certain dynamic conditions. When enabling these kinematic constraints, it is important to consider the typical motion profile of the application and ensure that the assumption underlying each constraint is satisfied most of the time.
Vertical gyro constraint
This constraint helps maintain good pitch and roll estimates during GNSS signal outages by allowing the accelerometers to be used to estimate pitch and roll of the vehicle in the local level frame. Regardless of user selection, this constraint is always enforced when the filter mode is “Vertical Gyro” or “AHRS” (see Filter States).
Assumption
The linear acceleration applied to the platform is zero.
Command
Vertical Gyro Constraint Control (0x0D,0x62)
Zero velocity update (velocity ZUPT)
This constraint helps stabilize the navigation solution during prolonged stationary periods. This constraint is useful for
Assumption
The platform is stationary when the reported velocity falls below the user provided threshold.
Command
Zero Velocity Update Control (0x0D,0x1E)
Zero angular rate update (angular rate ZUPT)
This constraint helps reduce gyro bias errors on the vertical (yaw) axis. This constraint is useful for ground vehicles which make prolonged stops, especially when no heading aid is available.
Assumption
The platform is not rotating when the angular rate estimate falls below a user provided threshold.
Command
Zero Angular Rate Update Control (0x0D,0x20)
Wheeled vehicle constraint
This constraint helps maintain a more accurate platform heading, especially during periods of low acceleration and poor
Assumption
Components of velocity perpendicular to the primary axis of the platform (as indicated by the mounting transformation) are zero.
Command
Wheeled Vehicle Constraint Control (0x0D,0x63)