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Ardupilot ekf3

Robotics / uav / ardupilot

An Extended Kalman Filter (EKF) algorithm is used to estimate vehicle position, velocity and angular orientation based on rate gyroscopes, accelerometer, compass, GPS, airspeed and barometric pressure measurements.

Parameter value Desc
EK3_ENABLE 1
AHRS_EKF_TYPE 3
EK3_IMU_MASK
EK3_PRIMARY
EK3_ALT_M_NSE Lower number reduces reliance on accelerometers, increases reliance on barometer.
EK3_GPS_TYPE Controls how GPS is used.
EK3_YAW_M_NSE Controls the weighting between GPS and Compass when calculating the heading

The EKF instantiates multiple instances of the filter called ‘lanes’. The primary lane is the one that provides state estimates, rest are updated in the background and available for switching to. The number of possible lanes is exactly equal to the number of IMUs enabled for use. Affinity is a way for the EKF lanes to use non-primary sensors within any running lane.

EK3_IMU_MASK and EKF3 instance

EK3_IMU_MASK 1 byte bitmap of IMUs to use in EKF3. A separate instance of EKF3 will be started for each IMU selected.

Bit IMU Binary Meaning
0 1 1 Use IMU 1
1 2 2 Use IMU 2
2 3 4 Use IMU 3

Version 4.6 EKF deprecated parameters

Configuration

1
2
EK3_IMU_MASK = 2
EK3_PRIMARY = 0   # Because only one EKF instance will run, and it's at index 0

1
2
EK3_IMU_MASK = 3 # IMU1 and IMU2 working and create two EKF instance
EK3_PRIMARY = 1   # To use the instance assigned to IMU2

Sensor affinity

ArduPilot EKF3 allows you to assign specific sensors (e.g., IMUs, GPS, barometers) to particular EKF "lanes" (instances). Each EKF lane can run in parallel, using different sensor combinations for redundancy and robustness.

Feature VISION_POSITION_ESTIMATE GLOBAL_VISION_POSITION_ESTIMATE
MAVLink ID 102 101
Frame of Reference Local frame (e.g., body or map-local) Global frame aligned to NED from origin
Position Fields x, y, z → meters x, y, z → meters
Orientation roll, pitch, yaw in radians roll, pitch, yaw in radians
Origin Definition Arbitrary local frame Aligned to a global origin (NED or ENU)
Units All in SI (meters, radians) All in SI (meters, radians)
Usage VIO, MoCap in local environments Global alignment (with known origin)

Reference