Pointing turtlebot to the target position before moving

edit

did you try to plot the odom and the cmd_vel ther is the rqt tools, to see waht is going inside, you may publisch the "angle_to_goal-theta"to see waht you input is

 def newOdom(msg):
        global x
        global y
        global theta
        x = msg.pose.pose.position.x
        y = msg.pose.pose.position.y

        q = (msg.pose.pose.orientation.x,
              msg.pose.pose.orientation.y,
              msg.pose.pose.orientation.z,
              msg.pose.pose.orientation.w)
         euler = euler_from_quaternion(q)
         theta = euler[2]

rospy.init_node("RobotController")
rospy.Subscriber("/robot1/odom", Odometry, newOdom)
pub = rospy.Publisher("/robot1/cmd_vel", Twist, queue_size = 1)
speed = Twist()
r = rospy.Rate(5)

goal = Point()
goal.x = 3.3
goal.y = 3.3
distance=sqrt(pow(goal.x-x,2) + pow(goal.y-y, 2))

inc_x = goal.x-x
inc_y = goal.y-y
angle_to_goal = atan2(inc_y, inc_x)
while abs(angle_to_goal - theta) > 0.1 :
    scale=1.5
    dir=(angle_to_goal-theta) /abs( angle_to_goal-theta)
    angSpeed= min(0.5, abs( angle_to_goal-theta) / scale)
    speed.angular.z = dir*angSpeed
    speed.linear.x = 0
    pub.publish(speed)
    r.sleep()


speed.angular.z = 0
while distance >= 0.7:
    distance=sqrt(pow(goal.x-x,2) + pow(goal.y-y, 2))
    rospy.loginfo(distance)
    speed.linear.x = 0.5
    speed.angular.z = 0
    pub.publish(speed)
    r.sleep()
speed.linear.x = 0.0
speed.angular.z =0.0
pub.publish(speed)

Have you seen #q313304 ? It's the same question so you should find what you want there.

I don't want my turtlebot to make angular movement while it is moving, because, angular movement in between is causing additional travel time

I don't see why you state that, if you don't turn when reaching a goal what would happen if the orientation is not completly accurate at the beginning ? Moreover, the robot could turn a little bit while moving forward which could lead to the robot never reaching the goal.

So I would advise you to reconsider this, it's not an issue to publish angular cmd_vel while moving forward.