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how to aggregate several PointCloud2 messages into one?

asked 2018-01-07 05:27:58 -0500

hanjuku-joshi gravatar image

updated 2018-01-07 17:37:16 -0500

ahendrix gravatar image

After converting my RPLIDAR's laser messages to PointCloud2 form (using hector_laser_to_pointcloud) I can visualize them in RVIZ and when doing rostopic echo I can see the messages coming through. How can I assemble the scans so I could get a collective cloud as I move my lidar around? I have my transforms set up and everything, thing is I am not sure as to how I can do this. Is there a package to do this?

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answered 2018-01-07 20:29:29 -0500

hanjuku-joshi gravatar image

I ended up using octomap_server for aggregating the pointcloud messages and used the frame_id as map. I converted laser_assembler to generate PointCloud2 messages, but I'm not sure it works. Regardless, here is the reworked laser_scan_assembler.cpp and periodic_snapshotter.cpp, respectively, for anyone who stumbles upon this thread:

#include "tf/transform_listener.h"
#include "tf/message_filter.h"
#include <ros/ros.h>
#include "laser_geometry/laser_geometry.h"
#include "sensor_msgs/LaserScan.h"
#include "sensor_msgs/PointCloud2.h"
#include "laser_assembler/base_assembler.h"
#include "filters/filter_chain.h"

using namespace laser_geometry;
using namespace std ;

namespace laser_assembler

 * \brief Maintains a history of laser scans and generates a point cloud upon request
class LaserScanAssembler
  LaserScanAssembler() : filter_chain_("sensor_msgs::LaserScan")
    // ***** Set Laser Projection Method *****
    private_ns_.param("ignore_laser_skew", ignore_laser_skew_, false);

    // configure the filter chain from the parameter server
    filter_chain_.configure("filters", private_ns_);

    // Have different callbacks, depending on whether or not we want to ignore laser skews.
    tf_filter_ = new tf::MessageFilter<sensor_msgs::LaserScan>(scan_sub_, *tf_, "base_link", 10);
    tf_filter_->registerCallback( boost::bind(&LaserScanAssembler::scanCallback, this, _1) );
    skew_scan_sub_ = n_.subscribe("scan", 10, &LaserScanAssembler::scanCallback, this);
  tf_filter_ = NULL;



  unsigned int GetPointsInScan(const sensor_msgs::LaserScan& scan)
    return (scan.ranges.size ());

  void ConvertToCloud(const string& fixed_frame_id, const sensor_msgs::LaserScan& scan_in, sensor_msgs::PointCloud2& cloud_out)
    // apply filters on laser scan
    filter_chain_.update (scan_in, scan_filtered_);

    // convert laser scan to point cloud
      int mask = laser_geometry::channel_option::Intensity +
             laser_geometry::channel_option::Distance +
             laser_geometry::channel_option::Index +
      projector_.transformLaserScanToPointCloud (fixed_frame_id, scan_filtered_, cloud_out, *tf_, mask);

  void scanCallback(const sensor_msgs::LaserScanConstPtr& laser_scan)
    if (!ignore_laser_skew_)
      ros::Duration cur_tolerance = ros::Duration(laser_scan->time_increment * laser_scan->ranges.size());
      if (cur_tolerance > max_tolerance_)
    ROS_DEBUG("Upping tf tolerance from [%.4fs] to [%.4fs]", max_tolerance_.toSec(), cur_tolerance.toSec());
    max_tolerance_ = cur_tolerance;

  bool ignore_laser_skew_;
  laser_geometry::LaserProjection projector_;
  tf::TransformListener* tf_ ;
  tf::MessageFilter<sensor_msgs::LaserScan>* tf_filter_;
  message_filters::Subscriber<sensor_msgs::LaserScan> scan_sub_;

  ros::Subscriber skew_scan_sub_;
  ros::Duration max_tolerance_;   // The longest tolerance we've needed on a scan so far
  ros::NodeHandle n_;
  ros::NodeHandle private_ns_;

  filters::FilterChain<sensor_msgs::LaserScan> filter_chain_;
  mutable sensor_msgs::LaserScan scan_filtered_;



using namespace laser_assembler ;

int main(int argc, char **argv)
  ros::init(argc, argv, "laser_scan_assembler");
  LaserScanAssembler pc_assembler;

  return 0;

    #include <cstdio>
#include <ros/ros.h>

// Services
#include "laser_assembler/AssembleScans.h"
#include "laser_assembler/AssembleScans2.h"

// Messages
#include "sensor_msgs/PointCloud.h"
#include "sensor_msgs/PointCloud2.h"

 * This a simple test app that requests a point cloud from the
 * point_cloud_assembler every 4 seconds, and then publishes the
 * resulting data
namespace laser_assembler

class PeriodicSnapshotter


    // Create a publisher for the clouds that we assemble
    pub_ = n_.advertise<sensor_msgs::PointCloud2> ("assembled_cloud", 1);

    // Create the service client for calling the assembler
    client_ = n_.serviceClient<AssembleScans2>("assemble_scans");

    // Start the timer that will trigger the processing loop (timerCallback)
    timer_ = n_.createTimer(ros::Duration(1,0), &PeriodicSnapshotter::timerCallback, this);

    // Need to track if we've called the timerCallback at least once
    first_time_ = true;

  void timerCallback(const ros::TimerEvent& e)

    // We don't want to build a cloud the first callback, since we we
    //   don't have a start and end time yet
    if (first_time_)
      first_time_ = false;

    // Populate our service request ...
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Hi, I am currently doing something similar to yours using a RPlidar A2 and a razor 9dof IMU. Can I check how did you changed your laser_assembler launch file?

HedgeHog gravatar image HedgeHog  ( 2020-03-06 02:25:33 -0500 )edit

answered 2018-01-07 14:16:16 -0500

There is the laser_assembler package for exactly this, is this what you're thinking of. If you've got the transformations updating as the LIDAR sensor is moving around then this should be all you need.

Hope this helps.

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Thanks! I already looked at laser assembler but found it easier to use hector_laserscan_to_pointcloud since it generated PointCloud2 messages while laser assembler did not.

hanjuku-joshi gravatar image hanjuku-joshi  ( 2018-01-07 20:26:02 -0500 )edit

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Asked: 2018-01-07 05:27:58 -0500

Seen: 1,192 times

Last updated: Jan 07 '18