ROS Answers: Open Source Q&A Forum - RSS feedhttps://answers.ros.org/questions/Open source question and answer forum written in Python and DjangoenROS Answers is licensed under Creative Commons Attribution 3.0Tue, 17 Feb 2015 23:57:54 -0600Information on message sensor_msgs/Imuhttps://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/Hi guyz,
I am new with ROS, and I am trying to use the output of the hector_mapping and my IMU data and fuse them into the robot_pose_ekf filter.
I wanted to have more information on the message units and frame of the data.
1)The angular_velocity is in rad/s or in deg/s ?
2)The linear acceleration are in g or in m/s^2 ?
3)What is the meaning of the covariance matrix? Shouldn't it be called the variance matrix? By definition :
> The variance is a measure of how far a
> set of numbers is spread out.
>
>
> The covariance is a measure of how
> much two random variables change
> together.
Since the measure of, for exemple, the acceleration, only depends on the accelerometers in the IMU, there is no point of using the covariance between the accelerometers, the gyrometers and the magnetometers since they are not related ...
Also, what are the units of the different covariance matrix?
I have also a suggestion: It could also be great documentation if each message description explained those information and not only the data types.
Cheers!
Fri, 01 Feb 2013 06:06:15 -0600https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/Comment by joq for <p>Hi guyz, </p>
<p>I am new with ROS, and I am trying to use the output of the hector_mapping and my IMU data and fuse them into the robot_pose_ekf filter.</p>
<p>I wanted to have more information on the message units and frame of the data. </p>
<p>1)The angular_velocity is in rad/s or in deg/s ?
2)The linear acceleration are in g or in m/s^2 ?</p>
<p>3)What is the meaning of the covariance matrix? Shouldn't it be called the variance matrix? By definition : </p>
<blockquote>
<p>The variance is a measure of how far a
set of numbers is spread out.</p>
<p>The covariance is a measure of how
much two random variables change
together.</p>
</blockquote>
<p>Since the measure of, for exemple, the acceleration, only depends on the accelerometers in the IMU, there is no point of using the covariance between the accelerometers, the gyrometers and the magnetometers since they are not related ...</p>
<p>Also, what are the units of the different covariance matrix? </p>
<p>I have also a suggestion: It could also be great documentation if each message description explained those information and not only the data types. </p>
<p>Cheers!</p>
https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?comment=54013#post-id-54013There was a brief problem with the message documentation generator, recently fixed. See: http://www.ros.org/doc/api/sensor_msgs/html/msg/Imu.htmlFri, 01 Feb 2013 13:05:58 -0600https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?comment=54013#post-id-54013Answer by Karan for <p>Hi guyz, </p>
<p>I am new with ROS, and I am trying to use the output of the hector_mapping and my IMU data and fuse them into the robot_pose_ekf filter.</p>
<p>I wanted to have more information on the message units and frame of the data. </p>
<p>1)The angular_velocity is in rad/s or in deg/s ?
2)The linear acceleration are in g or in m/s^2 ?</p>
<p>3)What is the meaning of the covariance matrix? Shouldn't it be called the variance matrix? By definition : </p>
<blockquote>
<p>The variance is a measure of how far a
set of numbers is spread out.</p>
<p>The covariance is a measure of how
much two random variables change
together.</p>
</blockquote>
<p>Since the measure of, for exemple, the acceleration, only depends on the accelerometers in the IMU, there is no point of using the covariance between the accelerometers, the gyrometers and the magnetometers since they are not related ...</p>
<p>Also, what are the units of the different covariance matrix? </p>
<p>I have also a suggestion: It could also be great documentation if each message description explained those information and not only the data types. </p>
<p>Cheers!</p>
https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?answer=53996#post-id-53996The dimensions of the angular velocity is in rad/s.
The linear acceleration goes with m/s^2.
As far the covariance goes it means that how two random variables change with respect to each other, So in this case it means that how much change in a particular dimension is linked to the other. As an example the covariance between X and Y dimension, similarly X and Z , Y and Z and so on. It does not mean between different sensors.
As far the units of the covariance matrix is concerned i think it is in the same units as that of the measurement it is associated with. Fri, 01 Feb 2013 06:29:57 -0600https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?answer=53996#post-id-53996Comment by tfoote for <p>The dimensions of the angular velocity is in rad/s.
The linear acceleration goes with m/s^2.
As far the covariance goes it means that how two random variables change with respect to each other, So in this case it means that how much change in a particular dimension is linked to the other. As an example the covariance between X and Y dimension, similarly X and Z , Y and Z and so on. It does not mean between different sensors.</p>
<p>As far the units of the covariance matrix is concerned i think it is in the same units as that of the measurement it is associated with. </p>
https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?comment=76777#post-id-76777Common units are defined in http://www.ros.org/reps/rep-0103.html REP 103Thu, 05 Sep 2013 12:21:12 -0500https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?comment=76777#post-id-76777Answer by asusrog for <p>Hi guyz, </p>
<p>I am new with ROS, and I am trying to use the output of the hector_mapping and my IMU data and fuse them into the robot_pose_ekf filter.</p>
<p>I wanted to have more information on the message units and frame of the data. </p>
<p>1)The angular_velocity is in rad/s or in deg/s ?
2)The linear acceleration are in g or in m/s^2 ?</p>
<p>3)What is the meaning of the covariance matrix? Shouldn't it be called the variance matrix? By definition : </p>
<blockquote>
<p>The variance is a measure of how far a
set of numbers is spread out.</p>
<p>The covariance is a measure of how
much two random variables change
together.</p>
</blockquote>
<p>Since the measure of, for exemple, the acceleration, only depends on the accelerometers in the IMU, there is no point of using the covariance between the accelerometers, the gyrometers and the magnetometers since they are not related ...</p>
<p>Also, what are the units of the different covariance matrix? </p>
<p>I have also a suggestion: It could also be great documentation if each message description explained those information and not only the data types. </p>
<p>Cheers!</p>
https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?answer=203332#post-id-203332if your IMU is outputting roll,pitch and yaw then your covariance matrix would be a 3x3 matrix. The diagonal elements represent variance of each measurement (eg: if variance of pitch is Ypp, roll is Xrr and yaw is Zyy).
Cov[0][0] = Xrr;
Cov[1][1] = Ypp;
Cov[2][2] = Zyy;
You can also fill out the non-diagonal elements which represent co-variance (how two variables change ). But the diagonal elements themselves should be enough for robot_pose_ekf.Tue, 17 Feb 2015 23:57:54 -0600https://answers.ros.org/question/53993/information-on-message-sensor_msgsimu/?answer=203332#post-id-203332