# What do x, y, and z denote in mavros topic /mavros/imu/data_raw

hi, I am using mavros to read the signals from the APM2.5. However I am not sure what x, y, z denote.

For example, in angular_velocity, I think the signals should be pitch, roll, and yaw in rad. How do x, y, and z correspond to them. Also, in linear_acceleration, what is the coordinates for x, y, and z, and are they in meter? Many thanks.

```
$ rostopic type /mavros/imu/data_raw
sensor_msgs/Imu
$ rosmsg show sensor_msgs/Imu
std_msgs/Header header
uint32 seq
time stamp
string frame_id
geometry_msgs/Quaternion orientation
float64 x
float64 y
float64 z
float64 w
float64[9] orientation_covariance
geometry_msgs/Vector3 angular_velocity
float64 x
float64 y
float64 z
float64[9] angular_velocity_covariance
geometry_msgs/Vector3 linear_acceleration
float64 x
float64 y
float64 z
float64[9] linear_acceleration_covariance
```

Also, how can I know the frequency of the signals. Many thanks.