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Hello,

I'm fairly new to ROS and was wondering if there was a way to convert a ".bag" laser scan file into a point cloud map. I have successfully run the "laser.bag" scan file, provided by ROS, in Rviz. Now I am curious to know how to turn this "laser.bag" file into a 3D map.

Thanks you for your time,

Tyler

Originally posted by tyler258 on ROS Answers with karma: 93 on 2011-09-16

Post score: 6

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One quick way to do this would be to use the laser_geometry node. It provides functionality for converting laser scans directly into PointCloud or PointCloud2 messages in the frame of your choice. That's what I use, and it's quite simple to do. I hope this helps.

EDIT: To use this functionality, you could do something like this:

In the class definition:

#include <ros/ros.h>
#include <tf/transform_listener.h>
#include <laser_geometry/laser_geometry.h>

class My_Filter {
     public:
        My_Filter();
        void scanCallback(const sensor_msgs::LaserScan::ConstPtr& scan);
     private:
        ros::NodeHandle node_;
        laser_geometry::LaserProjection projector_;
        tf::TransformListener tfListener_;

        ros::Publisher point_cloud_publisher_;
        ros::Subscriber scan_sub_;
};

My_Filter::My_Filter(){
        scan_sub_ = node_.subscribe<sensor_msgs::LaserScan> ("/scan", 100, &My_Filter::scanCallback, this);
        point_cloud_publisher_ = node_.advertise<sensor_msgs::PointCloud2> ("/cloud", 100, false);
        tfListener_.setExtrapolationLimit(ros::Duration(0.1));
}

In the callback function:

void My_Filter::scanCallback(const sensor_msgs::LaserScan::ConstPtr& scan){
    sensor_msgs::PointCloud2 cloud;
    projector_.transformLaserScanToPointCloud("base_link", *scan, cloud, tfListener_);
    point_cloud_publisher_.publish(cloud);
}

And the main:

int main(int argc, char** argv)
{
    ros::init(argc, argv, "my_filter");

    My_Filter filter;

    ros::spin();

    return 0;
}

Where "base_link" is the frame that you'd like to see all the scans in, *scan is the reference to the incoming laser scan, cloud is the sensor_msgs::PointCloud2 that you'd like to be your output (this can also be a regular sensor_msgs::PointCloud), and tfListener_ is your transform listener.

You must also add the following to your manifest.xml:

<depend package="laser_geometry"/>
<depend package="tf"/>
<depend package="sensor_msgs" />

That's how I build my LaserScans into point clouds. I can provide a more specific example if you need it.

EDIT: I have updated the code snippets such that if you paste all of the code into a .cpp file, build the file, and run it, it will work 100%. You should change "/scan" to the topic that your laser publishes, and you should change "/cloud" to the topic you wish to view the cloud on. In Rviz, add a new PointCloud2 visualizer and point it to the topic you chose for "/cloud" and it should work. This node also assumes that there is a tf from the frame of the laser to the target frame ("base_link" in this example).

Originally posted by DimitriProsser with karma: 11163 on 2011-09-16

This answer was ACCEPTED on the original site

Post score: 21

Original comments

Comment by acp on 2011-12-05:
How a tf from based_laser to based_link can be achieved?

Comment by DimitriProsser on 2011-09-26:
Just some advice, I wouldn't rename "/cloud" to "/base_link" because that could get confusing. You want "/cloud" to be the name of data stream, not the frame that it's in. To see it in Rviz, add a new PointCloud2 and link it to "/cloud" or whatever you've named it.

Comment by tyler258 on 2011-09-26:
Okay, I got the code running but I'm still having trouble publishing it in Rviz. The laser scan data I have publishes to tilt_scan. So I replaced "/scan" with "/tilt_scan" and I replaced "/cloud" with "/base_link" but this is still not working. Also, how do I get access to this new map?

Comment by tyler258 on 2011-09-23:
Would you mind providing the more specific example I would appreciate it. Right now I have my .cpp file set up, more or less, just like the example you provided. Now once I run the .cpp file, I run "rosbag play my_laser_data.bag" but I can't anything to show up in rviz.

Comment by tyler258 on 2011-09-21:
Could you explain how to call the transformLaserScanToPointCloud() function in the laser_gemoetry class?

Comment by AG1617 on 2013-05-14:
Running 12.04 and groovy, the following error comes up: /opt/ros/groovy/include/laser_geometry/laser_geometry.h:46:22: fatal error: Eigen/Core: No such file or directory

Any help?

Comment by Bernhard on 2013-06-05:
I had the same problem as you AG1617, you'll have to edit the file manually and fill in the correct path, usually the file is somewhere here /usr/include/eigen3/Eigen/core

Comment by RSA_kustar on 2014-07-20:
what is the difference between the target frame and frame id ?? the frame id for the /scan topic in my case is laser0_frame. So should it be the target frame or not ?

Comment by Mudassir Khan on 2014-07-31:
for /opt/ros/groovy/include/laser_geometry/laser_geometry.h:46:22: fatal error: Eigen/Core: No such file or directory try http://answers.ros.org/question/185948/eigencore-on-ros-hydro/

Comment by Tooght on 2016-11-30:
Hi .I followed the above steps but it didn't work. CMakeFiles/My_Filter.dir/src/My_Filter.cpp.o: In function My_Filter::My_Filter()': My_Filter.cpp:(.text+0x84): undefined reference to tf::Transformer::DEFAULT_CACHE_TIME' My_Filter.cpp:(.text+0x88): undefined reference to `tf::Transformer::DEFAULT

Comment by lounis on 2018-02-21:
Hi D. I came here as I want convert laserscans into pointcloud2. I've laserScans stored in a bag. I tried ur code. The error I get is with the difference in timestamps between laserscans, the bag (generated later on) and current time (tf's). I tried wth sim time but didnt work. Any help is wlcm.10x

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Hi,

Using Python to do the conversion simplifies a lot. Let's see how to do that using the laser_geometry package.

First, you need to launch the laser_geometry package from a launch file, properly configured. Here a suggested launch file:

<launch>
<node type="laser_scan_assembler" pkg="laser_assembler"
    name="my_assembler">
<remap from="scan" to="laser_scan"/>
<param name="max_scans" type="int" value="400" />
<param name="fixed_frame" type="string" value="my_robot_link_base" />
 </node>
  <node type ="laser2pc.py" pkg="laser_to_pcl" name="laser2pc"/>
</launch>

That file launches the laser_geometry package indicating that the frame from which the transform will be done is the my_robot_link_base (that is whatever tf link of your robot you want the point cloud to be refered from). Another parameter is the max_scans which indicates the max number of last scans that will be take into account for the computation of the point cloud ( this is useful in case your laser is rotating, so you can generate a full 3D cloud).

The launch file above also launches a second node that is the one you have to create to get the data and publish it into your selected topic. What should be the code of such a node? Check the following:

#!/usr/bin/env python

import rospy 
from laser_assembler.srv import AssembleScans2
from sensor_msgs.msg import PointCloud2

rospy.init_node("assemble_scans_to_cloud")
rospy.wait_for_service("assemble_scans2")
assemble_scans = rospy.ServiceProxy('assemble_scans2', AssembleScans2)
pub = rospy.Publisher ("/laser_pointcloud", PointCloud2, queue_size=1)

r = rospy.Rate (1)

while (True):
    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()

The code shows how to subscribe to the assemble_scans2 service. That is the one that will provide the point cloud on its answer. The code also shows that the point cloud will be published on a topic of type PoinCloud2. basically, the while loop what it does is, first, call to the service, then publish the answer of the service into a topic.

I have created a video (https://youtu.be/GvilxcePD64) showing how to use the laser_geometry with Python with a practical example.

Hope it helps.

Originally posted by R. Tellez with karma: 874 on 2017-07-24

This answer was NOT ACCEPTED on the original site

Post score: 4

Original comments

Comment by gvdhoorn on 2017-07-24:
As always with videos, please add a short description describing the main points / steps to your answer. If your video ever disappears, your answer becomes useless.

Comment by jayess on 2017-10-02:
This glosses over the meat of the question: how to turn a laser scan into a point cloud. Instead, you still direct people to look at your video. @DimitriProsser's answer is much more detailed and actually answers the question.

Comment by R. Tellez on 2017-10-03:
Thanks @jayess for stating what already was stated in the previous comment. As you can see in this answer I learnt the lesson, so no need to keep pushing. Use that time instead to answer yourself the question

Comment by jayess on 2017-10-03:
@R. Tellez: I'm commenting on the current version of this answer which was updated since the first comment. So, even if you have started giving more info on other answers this answer still glosses over relevant information and makes the user watch a video instead of getting an answer.

Comment by R. Tellez on 2017-10-09:
Modified to include everything

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