title: PCL Iterative Closest Point and other effects reporting empty point clouds
body: <p>i am using PCL with a pre-built version (1.9.1 for Windows) and even with building one with the source code, but i am not able to have iterative closest point (ICP) or even other filters (e.g., normal estimation) to properly work.
  here's my c++ code: </p>
  
  <pre><code>#include &lt;pcl/io/ply_io.h&gt;
  #include &lt;pcl/registration/icp.h&gt;
  
  void test(void) 
  { 
          typedef pcl::PointXYZ              PointType; 
          typedef pcl::PointCloud&lt;PointType&gt; PointCloudType;
  
          typedef pcl::IterativeClosestPoint&lt;PointType, PointType, float&gt; ICPType; 
  
          PointCloudType::Ptr pcA(new PointCloudType()); 
          pcl::io::loadPLYFile("pointcloud00000.ply", *pcA); 
          std::cout &lt;&lt; "pcA size: " &lt;&lt; pcA-&gt;points.size() &lt;&lt; std::endl; 
  
          PointCloudType::Ptr pcB(new PointCloudType()); 
          pcl::io::loadPLYFile("pointcloud00001.ply", *pcB); 
          std::cout &lt;&lt; "pcB size: " &lt;&lt; pcB-&gt;points.size() &lt;&lt; std::endl; 
  
          ICPType icp; 
          icp.setInputSource(pcA); 
          icp.setInputTarget(pcB); 
  
          PointCloudType pcC; 
          icp.align(pcC); 
          std::cout &lt;&lt; "pcC size: " &lt;&lt; pcC.points.size() &lt;&lt; std::endl; 
  } 
  </code></pre>
  
  <p>and this is what i get in the output console:</p>
  
  <pre><code>pcA size: 19346 
  pcB size: 19409 
  [pcl::KdTreeFLANN::setInputCloud] Cannot create a KDTree with an empty input cloud! 
  [pcl::KdTreeFLANN::setInputCloud] Cannot create a KDTree with an empty input cloud! 
  [pcl::IterativeClosestPoint::computeTransformation] Not enough correspondences found. Relax your threshold parameters. 
  pcC size: 19346 
  </code></pre>
  
  <p>there is some problem using the clouds, PCL complains about their emptiness but they are filled, as it is written, with about 20K points. </p>
  
  <p>can you please help me? </p>