Relation between cmd_vel and odometry twist data?

edit

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.