# Relation between cmd_vel and odometry twist data?

I have some short questions please if anyone can answer these questions.

Q1: What will be the unit of angle when we use

```
angle = tf::getYaw(odom.pose.pose.orientation);
```

Q2: What should be the unit of linear and angular velocity when setting cmd_vel of diffrential drive robots? i.e.

```
cmdvel_.linear.x = vt; // (m/s)
cmdvel_.angular.z = w; // (rad/s) is it ok?
```

Q3: What is the unit of `Odometry.twist.twist.angular.z`

?

Q4: If I want to find the previous velocity vector from Odometry data. Am I doing right? I want to find velocity vector in Odom frame?

```
linearV = (odom.twist.twist.linear.x);
angularV = (odom_globalVal.twist.twist.angular.z);
Vx = linearV * cos(angularV); // wrong::its not an angle its angular velocity
Vy = linearV * sin(angularV); // wrong
```

Thanks a lot.

I hope you got to solve your issue! Please, to select the correct Gmapping odometry model noise (srr, srt, str, stt): Is it correct to calculate the RMSE between /cmd_vel/linear/x and /odom/twist/twsit/linear/x for translation and RMSE between /cmd_vel/angular/z and /odom/twist/twist/angular/z for rotation ?