CODEWITHSUNDEEP
pythonrosrobotics
elihar
elihar

Reputation: 109

ROS TurtleBot 2 laser scanner seem to scan the side

I'm new to ROS, and I have a mission to develop an algorithm that allows the robot to move forward as long as he doesn't have an obstacle in front of him, but it kept getting stuck in obstacles that I've put in front of him in the gazebo simulation. When I checked it in depth, I figured that it seems that my robot scans to the sides instead of in front. And when I checked the specs for the scanner laser it said that the angles of the scan should be maximum between -90 degrees to 90 degrees and preferably much less than that. So it seems that I can't complete my mission due to "hardware" problems but it seems strange to me. Can anyone please help?

Here is my code:

#!/usr/bin/python
#
# stopper.py
#
#  Created on:
#      Author:
#

import rospy
import math
from geometry_msgs.msg import Twist
from sensor_msgs.msg import LaserScan

class Stopper(object):

    def __init__(self, forward_speed):
        self.forward_speed = forward_speed
        self.min_scan_angle = -10/180*math.pi
        self.max_scan_angle = 10 / 180 * math.pi
        self.min_dist_from_obstacle = 0.5
        self.keep_moving = True
        self.command_pub = rospy.Publisher("/cmd_vel_mux/input/teleop", Twist, queue_size=10)
        self.laser_subscriber = rospy.Subscriber("scan",LaserScan, self.scan_callback, queue_size=1)

    def start_moving(self):
        rate = rospy.Rate(10)
        rospy.loginfo("Starting to move")
        while not rospy.is_shutdown() and self.keep_moving:
            self.move_forward()
            rate.sleep()


    def move_forward(self):
        move_msg = Twist()
        move_msg.linear.x = self.forward_speed
        self.command_pub.publish(move_msg)

    def scan_callback(self, scan_msg):
        for dist in scan_msg.ranges:
            if dist < self.min_dist_from_obstacle:
                self.keep_moving = False
                break

Upvotes: 0

Views: 1548

Answers (1)

user10455554
user10455554

Reputation: 413

You should be able to select the angles you are interested in yourself. The -90 and +90 degrees are just the endpoints the laser scanner measures. So you get a dataset with a lot of distances in different angles. To detect obstacles in front of the robot you need to select a (or multiple) measurements in the middle of the dataset (my knowledge is rusty, I assume the ranges are sorted from -90° to 90° so 0° is in the middle of the array). So you may don't want to loop through all distances in msg.ranges but just a subset.

I found this tutorial that shows how to read out the data and access to the value from different angles.

Upvotes: 1

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