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
uint32 seq
time stamp
string frame_id
geometry_msgs/Quaternion orientation
float64 x
float64 y
float64 z
float64 w
float64 orientation_covariance
geometry_msgs/Vector3 angular_velocity
float64 x
float64 y
float64 z
float64 angular_velocity_covariance
geometry_msgs/Vector3 linear_acceleration
float64 x
float64 y
float64 z
float64 linear_acceleration_covariance
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Also, how can I know the frequency of the signals. Many thanks.

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In IMU message, x,y and z values under angular_velocity correspond to roll rate, pitch rate and yaw rate respectively. Because, roll is rotation around x axis, pitch is around y and yaw is around z. Angles are represented as quaternion under orientation . They are not Euler angles directly. You should convert them from Quaternion to Euler angles. Check Wikipedia for description about Quaternions: https://en.wikipedia.org/wiki/Quatern... .

linear_acceleration values should be represented as m/s^2 unless otherwise stated. You should check REP-103 ( http://www.ros.org/reps/rep-0103.html ) for dimension and coordinate standards in ROS.

For publish frequency of a topic you can use, rostopic hz /mavros/imu/data_raw

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Hi @Akif, thanks for your answer. I am confused about the quaternion representation for angular_velocity. I mean if the angular_velocity are under quaternion, there should be four values, namely x, y, z, and w, similar to the representation of orientation. Any hints on it?

Only orientation is represented as quaternion, angular velocity is not. Its message type is geometry_msgs/Vector3 and consists of x, y and z only.

@Akif, BTW, what is the output of a APM2.5 connected GPS. Is it a global NED position or a local position? Many thanks.