launching laser_scan_assembler with periodic snapshotter

edit

Start roscore and rosbag (I'm assuming that you are playing a pre-recorded bagfile)

Then use the laser_scan_assembler.launch file below. Of course, you can change the time buffer and maximum number of scans. I use the odom frame, but you can use map, if you prefer that!

<launch>
    <node pkg="laser_assembler" type="laser_scan_assembler" output="screen"  name="laser_scan_assembler">
    <param name="tf_cache_time_secs" type="double" value="475.0" />
    <param name="max_scans" type="int" value="4000000" />
    <param name="ignore_laser_skew" type="bool" value="true" />
    <param name="fixed_frame" type="string" value="/odom" />
  </node>
</launch>

Follow this with periodic snapshotter (rosrun periodic_snapshotter periodic_snapshotter) I use the periodic_snapshotter.cpp file below. You can change the time buffer for the snapshotter in the timerCallback

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

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

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


/***
 * This a simple test app that requests a point cloud from the
 * point_cloud_assembler every 80 seconds, and then publishes the
 * resulting data
 */
namespace laser_assembler
{

class PeriodicSnapshotter
{

public:

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

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

    // Start the timer that will trigger the processing loop (timerCallback)
    timer_ = n_.createTimer(ros::Duration(80,0), &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;
      return;
    }

    // Populate our service request based on our timer callback times
    AssembleScans srv;
    srv.request.begin ...