pr2controller tutorial, quaternion not the same for same program in python and cpp

I just went through pr2_controllers/Tutorials/Moving the arm through a Cartesian pose trajectory.

I tried to rewrite the client program from python to cpp. The program worked but got different quaternion vector(x,y,z,w) with the result from the original program.

The original code snippet from the tutorial:

#pretty-print list to string
def pplist(list):
  return ' '.join(['%2.3f'%x for x in list])

#print out the positions, velocities, and efforts of the right arm joints
if __name__ == "__main__":
rospy.init_node("test_cartesian_ik_trajectory_executer")
tf_listener = tf.TransformListener()
time.sleep(.5) #give the transform listener time to get some frames

# not needed, fix tutorial
joint_names = ["r_shoulder_pan_joint",
               "r_shoulder_lift_joint",
               "r_upper_arm_roll_joint",
               "r_elbow_flex_joint",
               "r_forearm_roll_joint",
               "r_wrist_flex_joint",
               "r_wrist_roll_joint"]

positions = [[.76, -.19, .83], [0.59, -0.36, 0.93]]
orientations = [[.02, -.09, 0.0, 1.0], [0.65, -0.21, .38, .62]]

success = call_execute_cartesian_ik_trajectory("/base_link", \
        positions, orientations)

#check the final pose
(trans, rot) = tf_listener.lookupTransform('base_link', 'r_wrist_roll_link', rospy.Time(0))
print "end Cartesian pose: trans", pplist(trans), "rot", pplist(rot)

The result pose is

 end Cartesian pose: trans 0.590 -0.360 0.930 rot 0.651 -0.211 0.381 0.621

which agrees with the result by doing rosrun tf tf_echo base_link r_wrist_roll_link

But the result of my program is

 end Cartesian pose: trans,0.59,-0.36,0.93,rol,0.83,-0.27,0.49,0.00 

Here is the code snippet:

   tf::TransformListener listener;
   ros::NodeHandle node;

   ROS_INFO("Now calling the client function...");
   success = call_execute_cartesian_ik_trajectory(node, "base_link", position, orientations);

   ROS_INFO("Finished calling");
   tf::StampedTransform transform;
   try{
      listener.lookupTransform("base_link", "r_wrist_roll_link", 
                           ros::Time(0), transform);
   }   
   catch (tf::TransformException ex){
      ROS_ERROR("%s",ex.what());
   }   

   ROS_INFO("end Cartesian pose: trans,%3.2f,%3.2f,%3.2f,rol,%3.2f,%3.2f,%3.2f,%3.2f \n ", transform.getOrigin().x(),transform.getOrigin().y(),transform.getOrigin().z(),transform.getRotation().getAxis().x(),transform.getRotation().getAxis().y(),transform.getRotation().getAxis().z(),transform.getRotation().getAxis().w());

I guess the error lies in misuse of the function transform.getRotation().getAxis().x()

Can someone point out what went wrong? Thanks.

Originally posted by vincent on ROS Answers with karma: 311 on 2011-08-08

Post score: 0

Original comments

Comment by vincent on 2011-08-08:
thanks for the info. And thank tfoote for editing.

Comment by Eric Perko on 2011-08-08:
Also keep in mind that "Closed" is used when admins/mods mark a question as a duplicate, offtopic, offensive, etc and technically doesn't mean the same thing as "Answered".

Comment by Eric Perko on 2011-08-08:
To mark a question as "Closed", please make sure that the correct answer is marked as "accepted". That is the green checkmark next to it (this question already has an accepted answer). There is no need to add a [Closed] to the title.