#include <ros/ros.h>
    #include <std_msgs/String.h>
    #include <sensor_msgs/PointCloud2.h>
    #include <pcl_ros/transforms.h>

    void callback(const sensor_msgs::PointCloud2ConstPtr  &cloud_msg)
    {
        ROS_INFO("Message recieved:"); //msg to c string
        Eigen::Matrix4f transform_1 = Eigen::Matrix4f::Identity();

        float theta = M_PI/18; // The angle of rotation in radians
        transform_1 (0,0) = cos (theta);
        transform_1 (0,1) = -sin(theta);
        transform_1 (1,0) = sin (theta);
        transform_1 (1,1) = cos (theta);

        printf ("Method #1: using a Matrix4f\n");
        std::cout << transform_1 << std::endl;
        sensor_msgs::PointCloud2 op_cloud;
        pcl_ros::transformPointCloud(transform_1,*cloud_msg,op_cloud);
    }

    int main (int argc, char **argv)
    {
        ros::init(argc, argv, "cloud_trfm");
        ros::NodeHandle nh;
        ros::Subscriber sub = nh.subscribe("/velodyne_points",1,callback); //topic name, buffer size untill node can read, callback fn
        ros::spin();
    }