title: Writing / Accessing points in a PointCloud2 structure C++ / ROS / PCL Library
body: <p>I am currently building a perception pipeline and am having trouble reading the points of my point cloud structure. I am reading in a point cloud into a PointCloud2 Structure and want to be able to write out the points in series of the point cloud or at the very least access them so I find a way to write them to a file later. The basic code I am working with is here:</p>
  <pre><code>void cloud_cropbox_cb(const sensor_msgs::PointCloud2ConstPtr &amp;cloud_msg)
  {
      // Container for original &amp; filtered data
      pcl::PCLPointCloud2 *cloud = new pcl::PCLPointCloud2;
      pcl::PCLPointCloud2ConstPtr cloudPtr(cloud);
      pcl::PCLPointCloud2 cloud_filtered;
  
      // convert given message into PCL data type
      pcl_conversions::toPCL(*cloud_msg, *cloud);
  </code></pre>
  <p>I want to be able to access the x,y,z elements of each point in the cloud and ideally just write them all out to a textfile. I have tried using <code>pcl::io::savePCDFileASCII()</code> but I don't think that is quite applicable here. An additional note is the base program is constantly running and never exits until manually closed I don't know if that will be relavent to writing out to a file. Any help on what exact functions to use / steps I need to take would be much appreciated.</p>