title: How to get the pointer of a pcl:PolygonMesh object
body: <p>I am a total newbie in C++ and PCL. I try to use <code>meshDecim.setInputMesh()</code> which needs a <code>pcl::PolygonMesh::Ptr</code>. I have got <code>pcl::PolygonMesh</code>.</p>
  <pre><code>pcl::PolygonMesh triangles; 
  pcl::PolygonMesh::Ptr meshOutput(new pcl::PolygonMesh()); 
  pcl::PolygonMesh::Ptr inp_ptr; 
  inp_ptr = triangles;                                           /////???? 
  pcl::MeshQuadricDecimationVTK meshDecim; 
  meshDecim.setInputMesh(inp_ptr);                     ///// from triangles 
  meshDecim.setTargetReductionFactor(0.5); 
  meshDecim.process(*meshOutput);
  </code></pre>