ECL EKF State Reset Logics

Remark: local frame refers static frame, body frame refers to the moving frame attached to the vehicle.

Possible Resets and Updated Flag

The reset logics for modern PX4 ECL EKF resides in ekf_helper.cpp. All resets are tracked by _state_reset_status struct, stored within uORB vehicle_local_position message (PublishLocalPosition()).

Reset Logic	Updated Flag	Delta Frame	uORB	MAVLink
resetHorizontalVelocityTo()	velNE_change, velNE_counter	local NED	delta_vxy, vxy_reset_counter	NIL
resetVerticalVelocityTo()	velD_change, velD_counter	local NED	delta_vz, vz_reset_counter	NIL
resetHorizontalPositionTo()	posNE_change, posNE_counter	local NED	delta_xy, xy_reset_counter	NIL
resetHeight()	posD_change , posD_counter	local NED	delta_z, z_reset_counter	NIL
resetQuatStateYaw()	quat_change, quat_counter	body frame?	delta_heading, heading_reset_counter	NIL

struct {    uint8_t velNE_counter;  ///< number of horizontal position reset events (allow to wrap if count exceeds 255)    uint8_t velD_counter;   ///< number of vertical velocity reset events (allow to wrap if count exceeds 255)    uint8_t posNE_counter;  ///< number of horizontal position reset events (allow to wrap if count exceeds 255)    uint8_t posD_counter;   ///< number of vertical position reset events (allow to wrap if count exceeds 255)    uint8_t quat_counter;   ///< number of quaternion reset events (allow to wrap if count exceeds 255)    Vector2f velNE_change;  ///< North East velocity change due to last reset (m)    float velD_change;  ///< Down velocity change due to last reset (m/sec)    Vector2f posNE_change;  ///< North, East position change due to last reset (m)    float posD_change;  ///< Down position change due to last reset (m)    Quatf quat_change;  ///< quaternion delta due to last reset - multiply pre-reset quaternion by this to get post-reset quaternion} _state_reset_status{};    ///< reset event monitoring structure containing velocity, position, height and yaw reset information

Suggestion: shall we expose the information to MAVLink for planning algorithms to work with?

Reference: vehicle_local_position.msg

# Fused local position in NED.
uint64 timestamp            # time since system start (microseconds)uint64 timestamp_sample                 # the timestamp of the raw data (microseconds)
bool xy_valid               # true if x and y are validbool z_valid                # true if z is validbool v_xy_valid             # true if vy and vy are validbool v_z_valid              # true if vz is valid
# Position in local NED framefloat32 x               # North position in NED earth-fixed frame, (metres)float32 y               # East position in NED earth-fixed frame, (metres)float32 z               # Down position (negative altitude) in NED earth-fixed frame, (metres)
# Position reset deltafloat32[2] delta_xyuint8 xy_reset_counter
float32 delta_zuint8 z_reset_counter
# Velocity in NED framefloat32 vx              # North velocity in NED earth-fixed frame, (metres/sec)float32 vy              # East velocity in NED earth-fixed frame, (metres/sec)float32 vz              # Down velocity in NED earth-fixed frame, (metres/sec)float32 z_deriv             # Down position time derivative in NED earth-fixed frame, (metres/sec)
# Velocity reset deltafloat32[2] delta_vxyuint8 vxy_reset_counter
float32 delta_vzuint8 vz_reset_counter# Acceleration in NED framefloat32 ax        # North velocity derivative in NED earth-fixed frame, (metres/sec^2)float32 ay        # East velocity derivative in NED earth-fixed frame, (metres/sec^2)float32 az        # Down velocity derivative in NED earth-fixed frame, (metres/sec^2)
float32 heading             # Euler yaw angle transforming the tangent plane relative to NED earth-fixed frame, -PI..+PI,  (radians)float32 delta_headinguint8 heading_reset_counter
# Position of reference point (local NED frame origin) in global (GPS / WGS84) framebool xy_global              # true if position (x, y) has a valid global reference (ref_lat, ref_lon)bool z_global               # true if z has a valid global reference (ref_alt)uint64 ref_timestamp            # Time when reference position was set since system start, (microseconds)float64 ref_lat             # Reference point latitude, (degrees)float64 ref_lon             # Reference point longitude, (degrees)float32 ref_alt             # Reference altitude AMSL, (metres)
# Distance to surfacefloat32 dist_bottom         # Distance from from bottom surface to ground, (metres)bool dist_bottom_valid          # true if distance to bottom surface is valid
float32 eph             # Standard deviation of horizontal position error, (metres)float32 epv             # Standard deviation of vertical position error, (metres)float32 evh             # Standard deviation of horizontal velocity error, (metres/sec)float32 evv             # Standard deviation of horizontal velocity error, (metres/sec)
# estimator specified vehicle limitsfloat32 vxy_max             # maximum horizontal speed - set to 0 when limiting not required (meters/sec)float32 vz_max              # maximum vertical speed - set to 0 when limiting not required (meters/sec)float32 hagl_min            # minimum height above ground level - set to 0 when limiting not required (meters)float32 hagl_max            # maximum height above ground level - set to 0 when limiting not required (meters)
# TOPICS vehicle_local_position vehicle_local_position_groundtruth# TOPICS estimator_local_position