def earth_accel2_df(IMU,IMU2,ATT):
    '''return earth frame acceleration vector from df log'''
    r = rotation_df(ATT)
    accel1 = Vector3(IMU.AccX, IMU.AccY, IMU.AccZ)
    accel2 = Vector3(IMU2.AccX, IMU2.AccY, IMU2.AccZ)
    accel = 0.5 * (accel1 + accel2)
    return r * accel
return earth frame acceleration vector from df log