what is the use of tf broadcast and how to move a part or a frame?

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hi , i am new to tf library and i am having trouble in understanding about how it works . went through this tutorial http://wiki.ros.org/tf/Tutorials but still i have few doubts with how things are suppose to work

hear are my doubts 1. i created a fixed frame and i am moving it in this following way . is this a correct method to move a frame . if not suggest how to move ,rotate a frame or object in tf and rviz

#!/usr/bin/env python

import rospy
import tf

if __name__ == '__main__':
    rospy.init_node('my_tf_broadcaster')
    br = tf.TransformBroadcaster()
    rate = rospy.Rate(1.0)
    x=0.0
    z=2.0
    while not rospy.is_shutdown():
        br.sendTransform((0.0, x, z),
                         (0.0, 0.0, 0.0, 1.0),
                         rospy.Time.now(),
                         "robotframe",
                         "map")
        print "frame send"
        x+=0.1
        if x > 5:
            x=0
            print "x exceeded the limit"
        rate.sleep()

hear i just create a frame(robotframe) and move this frame by incrementing the x axis value ..is this the correct method if not , guide me in moving a frame

1. what is the use of tf broadcast http://wiki.ros.org/tf/Tutorials/Writ... is tf broadcast is used to move a frame or object in ros??

2. in the turtle tutorial on tf , we studied how to use listener and broadcast , but how is the turtle moving with respect to the keypress .i know how to detect key so my question is , how the turtles frame is moving .

3. if i like to move the carrot frame without changing turtle2 . how to do that

if example codes can be provided in python . it will be a great help for me thank you