A script for Windows to communicate with ROS hokuyo_node over rosbridge.

subscribe_hokuyo_node_via_rosbridge.py

# -*- coding: utf-8 -*-
"""
Created on Sat Oct 28 22:14:57 2016

@author: sakurai
---------------------------------------

This script is for Windows to communicate with ROS hokuyo_node over rosbridge.

Install rosbridge on the remote machine.
$ sudo apt-get install ros-indigo-rosbridge-suite
$ sudo apt-get install ros-indigo-hokuyo-node

Run the youbot driver and the rosbridge TCP server.
$ roscore
$ rosparam set hokuyo_node/port /dev/ttyACM1
$ rosrun hokuyo_node hokuyo_node
$ roslaunch rosbridge_server rosbridge_tcp.launch

Run this script and scans are plotted.
"""

import socket
import json
from datetime import datetime
import matplotlib.pyplot as plt


class HokuyoNode(object):
    def __init__(self, rosbridge_host='192.168.100.40', rosbridge_port=9090):
        self.sock = socket.socket()
        self.sock.connect((host, port))
        json_str = json.dumps(dict(op='subscribe', topic='/scan'))
        self.sock.send(json_str)
        self.str_buffer = ""
        self.jsons = []

    def receive_scan(self):
        '''
        returns `sensor_msgs/LaserScan` message as a dict.
        see http://docs.ros.org/kinetic/api/sensor_msgs/html/msg/LaserScan.html
        '''
        while True:
            partial_str = self.sock.recv(100000)
            self.str_buffer += partial_str
            # insert ! as  delimiter
            self.str_buffer = self.str_buffer.replace('{"topic"',
                                                      '!{"topic"')
            splits = self.str_buffer.split("!")
            self.str_buffer = splits[-1]
            self.jsons += splits[:-1]

            if len(self.jsons):
                json_str = self.jsons.pop()
                # discard if json_str is not a complete json string
                if json_str.endswith('"publish"}'):
                    laser_scan = json.loads(json_str)['msg']
                    return laser_scan

    def close(self):
        self.sock.close()


if __name__ == '__main__':
    # address and port of rosbridge
    host = '192.168.100.40'
    port = 9090

    hokuyo = HokuyoNode(host, port)  # subscribe `/scan` topic

    try:
        while True:
            # receive `sensor_msgs/LaserScan` message
            laser_scan = hokuyo.receive_scan()

            header = laser_scan['header']

            seq = header['seq']
            print "seq:", seq

            stamp = header['stamp']
            date_time = datetime.fromtimestamp(
                stamp['secs']).strftime('%Y/%m/%d %H:%M:%S')
            date_time += ".{}".format(stamp['nsecs'] // 100000)
            print date_time

            ranges = laser_scan['ranges']
            plt.plot(ranges)
            plt.title('# ' + str(seq))
            plt.show()

    except KeyboardInterrupt:
        pass

    hokuyo.close()