How to subscribe "/scan" topic, modify message Laserscan.ranges and publish it to the new topic?

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1

I would like to improve the LDS-01 sensor of the turtlebot3 by subscribing the message.ranges, modify the messange.ranges by applying some algorithm and publish it to the new topic as shown below. But there are an error when I run the coding. The error is

  1. There are overflow encountered.
  2. When I subscribing the new topic which is “/scan_new”, the error is “WARNING: no messages received and simulated time is active. Is /clock being published?”.

May I know why? and is there anyone can help with my coding? Thank you in advance!

#! /usr/bin/env python

import rospy
from sensor_msgs.msg import LaserScan   
from numpy import *
import numpy as np

def callback(msg):
    x1 = msg.ranges
    x2 = np.array(x1,dtype=float)
    #input 1
    x1_xoffset = 0.1656566113
    x1_gain = 0.599818245108751
    x1_ymin = -1

    #layer 1
    b1 = matrix ('-326.80027082597098342;-98.990085738415288574;83.870582554028558775;-72.368630055558369918;-0.7092849798153298968;57.269078212651997717;44.310310623213219117;-31.707975756385888388;-17.911078072875334044;-4.6394718363325218036')
    IW1_1 = matrix ('337.00974203853263589;112.59115212423027685;-110.55255345932357613;113.22379022448127728;1.3919097878355670694;-110.07199451465535844;-110.63343956448693461;112.90214029452344846;111.7555578995358303;114.3437445151164269')

    #layer 2
    b2 = matrix ('-2.978824073708045072e-05')
    LW2_1 = matrix ('0.030307489543199929438 0.060616873246115143825 -0.060618376238034066272 0.060619146713019073092 -0.00016486744836432447401 -0.060619845018730772468 -0.060619496805093056602 0.060618473675156582525 0.060617195348181586445 0.060615509952774870861')

    # Output 1
    y1_ymin = -1
    y1_gain = 0.606060606060606
    y1_xoffset = 0.2

    #input 1
    xp1 = ((x2 - x1_xoffset)*(x1_gain))+x1_ymin

    #layer 1
    n1 = IW1_1*xp1+b1
    a1 = 2/(1+exp(-2*n1))-1

    #layer 2
    a2 = LW2_1*a1+b2

    # Output 1
    y1 = ((a2-y1_ymin)/(y1_gain))+y1_xoffset
    y2 = y1.tolist()
    scan.ranges = y2
    pub.publish(scan)

rospy.init_node("ann_publisher")
sub = rospy.Subscriber('/scan', LaserScan, callback)
pub = rospy.Publisher('/scan_new', LaserScan, queue_size=1)
rate = rospy.Rate(2)
scan = LaserScan()
rospy.spin()
2

To solve this problem you just need to edit your coding like this

y1 = ((a2-y1_ymin)/(y1_gain))+y1_xoffset
y2 = y1.tolist()[0]

This is because the value of y2 = y1.tolist(),is [[1, 2, 3]] which is in matrix. But if you adding the y2 = y1.tolist()[0] the value of y2 will become [1, 2, 3] which is the true value of the ranges.