How to get robot position by slam_out_pose?

edit

hi please help, i made my own robot to evaluate position of the robot. i'm using Lidar hector_slam that release topic slam_out_pose. so i call the variable in position and orientation. but i'm not sure if i'm doing this correctly. i'm not using IMU or TICK i just want Lidar that can evaluate the position. if the robot pointing to the goal, the robot will go forward else rotate until the goal founded. the problem is when i try to rotate until exactly X position, it's not moving forward (print'forward')

robot specs;

1. ydlidar x4
2. Raspberry pi 3b+
3. 2 DC Motor
4. Motor Driver H Bridge

view_frames; https://drive.google.com/file/d/10ESa...

here's the screenshot of slam_out_pose; https://ibb.co/ZMdWRyx

#! /usr/bin/env python

import rospy
import RPi.GPIO as GPIO
import time
from geometry_msgs.msg import PoseStamped
from geometry_msgs.msg import Point
from math import atan2

x = 0.0
y = 0.0
theta = 0.0

def newOdom (msg):
    global x
    global y
    global theta

    x = msg.pose.position.x
    y = msg.pose.position.y

    rot_q = msg.pose.orientation
    (roll, pitch, theta) = euler_from_quaternion ([rot_q.x, rot_q.y, rot_q.z, rot_q.w])

sub = rospy.Subscriber("/slam_out_pose", PoseStamped, newOdom)

GPIO.setmode(GPIO.BCM)
GPIO.setup(7,GPIO.OUT)
GPIO.setup(8,GPIO.OUT)
GPIO.setup(9,GPIO.OUT)
GPIO.setup(10,GPIO.OUT)

fright = GPIO.output(9,True)
bright = GPIO.output(10,True)
fright = GPIO.output(7,True)
bright = GPIO.output(8,True)

goal = Point ()
goal.x = 2
goal.y = 2

while not rospy.is_shutdown():
    inc_x = goal.x - x
    inc_y = goal.y - y

    angle_to_goal = atan2 (inc_y, inc_x)

    if abs(angle_to_goal - theta) > 0.1:
        print("ROTATE RIGHT")
        fright
    else:
        print("FORWARD")
        fright
        bright

i hope someone can explain to me thank you.