How to convert LaserScan to PCLPointCloud2?

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Currently, I'm trying to read the laserscanner data and convert to PCLPointCloud2 for processing. I took the pcl_ros tutorial code and adapted the callback parameter to sensor_msgs::LaserScan. However, I get a compiler error:

/usr/include/boost/function/function_template.hpp:118:11: error: invalid initialization of reference of type ‘const sensor_msgs::LaserScan_<std::allocator<void> >&’ from expression of type ‘const boost::shared_ptr<const sensor_msgs::LaserScan_<std::allocator<void> > >’

This is the code:

#include <ros/ros.h>
// PCL specific includes
#include <sensor_msgs/PointCloud2.h>
#include <sensor_msgs/LaserScan.h>
#include "laser_geometry/laser_geometry.h"
#include <pcl_conversions/pcl_conversions.h>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>

#include <pcl/filters/voxel_grid.h>

ros::Publisher pub;

void cloud_cb(const sensor_msgs::LaserScan &scan_msg)
{
    // Container for original & filtered data
    pcl::PCLPointCloud2 *cloud = new pcl::PCLPointCloud2;
    pcl::PCLPointCloud2ConstPtr cloudPtr(cloud);
    pcl::PCLPointCloud2 cloud_filtered;

    // Convert to PCL data type
    laser_geometry::LaserProjection projector_;
    sensor_msgs::PointCloud2 pntCloud;
    projector_.projectLaser(scan_msg, pntCloud, 30.0);

    pcl_conversions::toPCL(pntCloud, *cloud);

    // Perform the actual filtering
    pcl::VoxelGrid<pcl::PCLPointCloud2> sor;
    sor.setInputCloud(cloudPtr);
    sor.setLeafSize(0.1, 0.1, 0.1);
    sor.filter(cloud_filtered);

    // Convert to ROS data type
    sensor_msgs::PointCloud2 output;
    pcl_conversions::moveFromPCL(cloud_filtered, output);

    // Publish the data
    pub.publish(output);
}

int main(int argc, char **argv)
{
    // Initialize ROS
    ros::init(argc, argv, "my_pcl_tutorial");
    ros::NodeHandle nh;

    // Create a ROS subscriber for the input point cloud
    ros::Subscriber sub = nh.subscribe<sensor_msgs::LaserScan>("input", 1000, &cloud_cb);

    // Create a ROS publisher for the output point cloud
    pub = nh.advertise<sensor_msgs::PointCloud2>("output", 1);

    // Spin
    ros::spin();
}

I can change the callback paramater to const sensor_msgs::LaserScan::ConstPtr&. However, I have issue with the projector_.projectLaser(scan_msg, pntCloud, 30.0); since this fucntion needs LaserScan&. How can I fix this code?