RT_INS_Vel_ECEF_1: Accuracy and INS X Velocity
RT_INS_Vel_ECEF_1: 142, 18 (0x8E1220 + unit id) (0x392)
Byte 0: Validity
Byte 1: Accuracy X
Byte 2: Accuracy Y
Byte 3: Accuracy Z
Bytes 4-6: INS ECEF velocity X (m/s)
ECEF velocities are velocities in the Earth-Centered co-ordinate frame.
Speed resolution is m/s * 1e-4
Accuracy resolution is m/s * 1e-2
Accuracy is an approximation to the 1 sigma standard deviation of the velocity value.