extract SensorMessages/LaserScan from SensorMessages/PointCloud2 created in simulation

Question

Hello all,

This is my problem: v-rep publishes data from a simulated LMS100 in the form of SensorMessages/PointCloud2 on ROS, but i need SensorMessages/LaserScan. I have installed the pointcloud_to_laserscan package but it seems to be only for Kinect. I have no idea how to use it with pointcloud data already there(and not from Kinect).Can anyone help me with that please?

Thanks in advance.

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Originally posted by Yami on ROS Answers with karma: 1 on 2013-10-07

Post score: 0

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Original comments

Comment by jdorich on 2013-10-07:
you may just need to adjust some parameters. The pointcloud_to_laserscan essentially just takes a horizontal slice from the point cloud and makes that the "laser scan". The points in the point cloud could be out of that height range.

Comment by Yami on 2013-10-07:
Thanks jdorich, but the problem is i have no idea how to use this pointcloud_to_laserscan package. So I wrote my own node which subscribes for pointclouds in vrep,

#include "ros/ros.h"

#include "std_msgs/String.h"

#include <sensor_msgs/PointCloud2.h>

#include <sensor_msgs/LaserScan.h>

/**

• subscribe pointcloud from v-rep */ void cloudCallback(const sensor_msgs::PointCloud2::ConstPtr& Cloud) { ROS_INFO("Clouds Received"); }

int main(int argc, char **argv) {

ros::init(argc, argv, "cloudtoscan");

ros::NodeHandle n;

ros::Subscriber cloud_sub = n.subscribe("/vrep/PointCloud2", 100, cloudCallback);

Comment by Yami on 2013-10-07:
But from here i don't know how to write the program. I know how to change point data to angle data, but do not know how to do that in every single scan. Can u please help me with that?

Answer 1

I believe you can run the pointcloud_to_laserscan for any Sensor_msgs/PointCloud2 data by the following (in this case I've matched what you have put above for the vrep):

<launch>
  <!-- Fake Laser Standalone nodelet-->
  <node pkg="nodelet" type="nodelet" name="vrep_laser" args="standalone pointcloud_to_laserscan/CloudToScan" respawn="true">
    <param name="output_frame_id" value="/vrep_frame"/>
    <param name="min_height" value="-0.15"/>
    <param name="max_height" value="0.15"/>
    <remap from="cloud" to="/vrep/PointCloud2"/>
  </node> 

</launch>

Adjust the "output_frame_id", "min_height", and "max_height" as necessary for the vrep Sensor_msgs/PointCloud2 data.

This tutorial has information on nodelets and running standalone nodelets and this turtlebot file shows an example for how to run the pointcloud_to_laserscan nodelet. The code I have above follow these.

Hopefully this helps.

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Originally posted by jdorich with karma: 211 on 2013-10-08

This answer was ACCEPTED on the original site

Post score: 0

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Original comments

Comment by Yami on 2013-10-09:
Thanks a lot jdorich . That is exactly what i looked for.

Comment by jdorich on 2013-10-10:
Great! See updated answer. I forgot that you could set standalone as an arg rather than loading a standalone nodelet manager.

Comment by Yami on 2013-10-10:
thanks again