title: How can I get the PointIndices of a given PointCloud?
body: <p>For example:</p>
  
  <pre><code>pcl::PointCloud&lt;pcl::PointXYZI&gt;::Ptr example_cloud(new pcl::PointCloud&lt;pcl::PointXYZI&gt;);
  
  //cloud is populated
  
  pcl::PointIndices::Ptr point_indices(new pcl::PointIndices); 
  </code></pre>
  
  <p>How do I populate point_indices with the indices of example_cloud?</p>