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Applying restrictions on 360-degree LiDAR for slam and autonomous navigation

asked 2017-12-20 02:53:35 -0500

maziarser gravatar image

I am working with TurtleBot 3-Burger (Rasberry Pi 3) and ROS Kinetic.

On Turtlebot 3, we have a 360-degree Planner LiDAR for slam and autonomous navigation.

What I need/want to do is to make this scanner looking at certain angles for data collection.

For example, I want it to collect the data from those angles which are highlighted using Slashes (front and rear), and ignore the data from those angles which are highlighted using Brackets (left and right).

  \                              /
     \                          /
      \                        /
       ]                       [    
       ]                       [      
       ] ]   LiDAR Scanner   [ [
       ]                       [    
       ]                       [    
       /                       \
     /                          \
   /                              \

**Sorry for my figure, I can't upload the actual image as i am new in ROS community and I don't have enough points to upload an image.

Any help and hint needed and I will appreciate it.

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3 Answers

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answered 2018-01-05 02:28:56 -0500

maziarser gravatar image

updated 2018-01-05 02:41:54 -0500

I have solved this issue and I was thinking that sharing the real solution is a good idea with others:

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

ranges_filter = []
intensities_filter = []

#copy the range and intensities of "/scan" topic to "ranges_filter" and "intensities_filter" 
#you need to convert them to "list" as "data.ranges" and "data.intensities" are "tuple"
def callback_scan(data):
    global ranges_filter, intensities_filter

    len(data.ranges) #360
    len(data.intensities) #360

    ranges_filter = copy.copy(data.ranges)
    intensities_filter = copy.copy(data.intensities)

    #convert them to list
    ranges_filter = list(ranges_filter)
    intensities_filter = list(intensities_filter)

     #filtering those angles that I do not want them (based on the question)
    for x in range(45, 135):
        ranges_filter[x] = 0
        intensities_filter[x] = 0

    for y in range(225, 315):
        ranges_filter[y] = 0
        intensities_filter[y] = 0

#define a new topic called "filterScan" to store all laser scanner data
rospy.init_node('laser_scan_filter')

scan_pub = rospy.Publisher('filterScan', LaserScan, queue_size=50)

rospy.Subscriber("/scan", LaserScan, callback_scan) 

#it is based on the type of laser scanner (length of data.ranges)
num_readings = 360
laser_frequency = 60

count = 0
r = rospy.Rate(1.0)
while not rospy.is_shutdown():
    current_time = rospy.Time.now()

    filterScan = LaserScan()

    filterScan.header.stamp = current_time
    filterScan.header.frame_id = 'base_scan'
    filterScan.angle_min = 0 # start angle of the scan [rad]
    filterScan.angle_max = math.pi * 2  # end angle of the scan [rad]
    filterScan.angle_increment = 0.0174532923847 # angular distance between measurements [rad]
    filterScan.time_increment = 2.98699997074e-05 # time between measurements [seconds]
    filterScan.range_min = 0.0 # minimum range value [m]
    filterScan.range_max = 3.5 # maximum range value [m]

    filterScan.ranges = []
    filterScan.intensities = []


    for i in range(0, num_readings-1):
        filterScan.ranges = copy.copy(ranges_filter)

        filterScan.intensities = copy.copy(intensities_filter)

    scan_pub.publish(filterScan)
    r.sleep()

I have done it in Python and the code is working perfectly fine for Turtlebot3-Burger.

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Comments

+1 for posting your solution, that is always appreciated.

Was there any specific reason you could not use one of the filters from the laser_filters package?

gvdhoorn gravatar image gvdhoorn  ( 2018-01-05 02:50:29 -0500 )edit

@gvdhoom, thanks for your comment. No, that would be another solution. I think, the posted answer can help those people who are making apps for end users to work with robots.

maziarser gravatar image maziarser  ( 2018-01-05 03:23:08 -0500 )edit

Hello, I edited the turtlebot3_slam.launch and put a node for laser_filters over there. Furthermore, I created another file test.yaml in the same location of the launch file and put the maximum and minimum angles. The launch file ran without error but there was no change according to the filter.

sujeet gravatar image sujeet  ( 2018-07-29 15:18:31 -0500 )edit
0

answered 2017-12-20 03:32:24 -0500

You can maybe use the laser filter package to extract the LaserScan data accordingly to the angle boundaries. Or just Subscribe the LaserScan data published to the system , find out which index is the starting index of the laser and use it.

I used these idea to implement the node which prevent robot to crash the obstacle in the front

by using the frontage angle and modify the "cmd_vel" to prevent crashing in front side too.

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Comments

Thanks for your reply. Did you publish your previous job somewhere which is open to public and I can see how it works?

maziarser gravatar image maziarser  ( 2017-12-20 06:14:47 -0500 )edit

Hello, I edited the turtlebot3_slam.launch and put a node for laser_filters over there. Furthermore, I created another file test.yaml in the same location of the launch file and put the maximum and minimum angles. The launch file ran without error but there was no change according to the filter.

sujeet gravatar image sujeet  ( 2018-07-29 15:18:44 -0500 )edit
0

answered 2017-12-20 03:34:25 -0500

write a node that subscribes to the published data, strips out the values you don't want and publishes it on a new topic - you could replace the unwanted values with NaN, or publish two laser scans as front and rear, depending on how you are going to use the data

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Comments

Thanks for your comment. Is it possible for me to have more explanation about your hint?

maziarser gravatar image maziarser  ( 2017-12-20 06:21:10 -0500 )edit

Hello, I edited the turtlebot3_slam.launch and put a node for laser_filters over there. Furthermore, I created another file test.yaml in the same location of the launch file and put the maximum and minimum angles. The launch file ran without error but there was no change according to the filter.

sujeet gravatar image sujeet  ( 2018-07-29 15:19:19 -0500 )edit

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Asked: 2017-12-20 02:53:35 -0500

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Last updated: Jan 05 '18