VehicleOpticalFlow (UORB message) 
Optical flow in XYZ body frame in SI units.
c
# Optical flow in XYZ body frame in SI units.
uint64 timestamp               # time since system start (microseconds)
uint64 timestamp_sample
uint32 device_id               # unique device ID for the sensor that does not change between power cycles
float32[2] pixel_flow          # (radians) accumulated optical flow in radians where a positive value is produced by a RH rotation about the body axis
float32[3] delta_angle         # (radians) accumulated gyro radians where a positive value is produced by a RH rotation about the body axis. (NAN if unavailable)
float32 distance_m             # (meters) Distance to the center of the flow field (NAN if unavailable)
uint32 integration_timespan_us # (microseconds) accumulation timespan in microseconds
uint8 quality                  # Average of quality of accumulated frames, 0: bad quality, 255: maximum quality
float32 max_flow_rate          # (radians/s) Magnitude of maximum angular which the optical flow sensor can measure reliably
float32 min_ground_distance    # (meters) Minimum distance from ground at which the optical flow sensor operates reliably
float32 max_ground_distance    # (meters) Maximum distance from ground at which the optical flow sensor operates reliably