Laser_assemble for Hokuyo scans in Gazebo

Question

Hi everyone!

I'm trying to assemble some readings from a Hokuyo laser simulated in gazebo.

The assembler I'm trying to use is the one you can download here: https://github.com/ros-perception/laser_assembler

Once I have downloaded and catkin_maked it, I run the gazebo simulation, which publish the topic /mybot/laser/scan with the planar scan. I can perfectly visualize that scan in rviz by setting the fixed frame to a topic called "odom" and adding a LaserScan with the /mybot/laser/scan topic.

Then, I create the following launch file called "hokuyo_assembler.launch":

<launch>
  <node pkg="laser_assembler" type="laser_scan_assembler" output="screen"  name="laser_scan_assembler">
    <remap from="/mybot/laser/scan" to="assebled_scan"/>
    <param name="tf_cache_time_secs" type="double" value="10.0" />
    <param name="max_scans" type="int" value="400" />
    <param name="ignore_laser_skew" type="bool" value="true" />
    <param name="fixed_frame" type="string" value="odom" />
  </node>
</launch>

but when I try in a new terminal "roslaunch laser_assembler hokuyo_assembler.launch", it does not publish any new topic, it only says the following:

SUMMARY

PARAMETERS
 * /laser_scan_assembler/fixed_frame: odom
 * /laser_scan_assembler/ignore_laser_skew: True
 * /laser_scan_assembler/max_scans: 400
 * /laser_scan_assembler/tf_cache_time_secs: 10.0
 * /rosdistro: kinetic
 * /rosversion: 1.12.7

NODES
  /
    laser_scan_assembler (laser_assembler/laser_scan_assembler)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
process[laser_scan_assembler-1]: started with pid [13103]
[ INFO] [1501870597.118463994]: TF Cache Time: 10.000000 Seconds
[ INFO] [1501870597.122609645]: Max Scans in History: 400
[ INFO] [1501870597.128738188]: Fixed Frame: odom

Any idea of how can I create the topic with the assembled scans?

Thanks in advance.

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Originally posted by Burgos on ROS Answers with karma: 1 on 2017-08-04

Post score: 0

Answer 1

Hello,

As @tfoote says, the first thing you need to do is remap the scan topic to the one where the laser data is being published in your case. Here you have an example launch file (where the Hokuyo data is published into the /kobuki/laser/scan topic):

<launch>
  <node pkg="laser_assembler" type="laser_scan_assembler" output="screen"  name="laser_scan_assembler">
    <remap from="scan" to="/kobuki/laserscan"/>
    <param name="tf_cache_time_secs" type="double" value="10.0" />
    <param name="max_scans" type="int" value="400" />
    <param name="ignore_laser_skew" type="bool" value="true" />
    <param name="fixed_frame" type="string" value="base_link" />
  </node>
</launch>

Also, the output provided by the laser_scan_assembler node is given through services, so you will need to perform a call to that service in order to get the Pointcloud data associated to your laser readings. Here you have an example code that does that:

#!/usr/bin/env python

import rospy 
from laser_assembler.srv import *
from sensor_msgs.msg import PointCloud2

rospy.init_node("client_test")
rospy.wait_for_service("assemble_scans2")
assemble_scans = rospy.ServiceProxy('assemble_scans2', AssembleScans2)
pub = rospy.Publisher ("/pointcloud", PointCloud2, queue_size=1)
r = rospy.Rate (1)

while not rospy.is_shutdown():
    try:
        resp = assemble_scans(rospy.Time(0,0), rospy.get_rostime())
        print "Got cloud with %u points" % len(resp.cloud.data)
        pub.publish (resp.cloud)

    except rospy.ServiceException, e:
        print "Service call failed: %s"%e

    r.sleep()

So basically, what this code does is to perform calls to the /assemble_scan2 service, which provides the PointCloud2 data, and then publish this data into a topic, so you can, for instance, visualize it in RViz.

I have also created this video whith the whole process which I think it may help you understand it better.

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Originally posted by Alberto E. with karma: 356 on 2017-10-23

This answer was ACCEPTED on the original site

Post score: 0