title: How to read vector<vector<Point3f> > from xml file with filestorage
body: <p>I was wondering if it was possible to load a vector of vector of Point2f from an xml file, using the cv::FileStorage class.</p>
  
  <p>This is what I tried for saving:</p>
  
  <pre><code>filestorage  &lt;&lt; "ObjPoints" &lt;&lt; "{";
  for (int i = 0; i &lt; objPoints.size(); ++i)
  {
      Mat outMat(objPoints[i]);
      filestorage &lt;&lt; "ObjPoints_" + IntToString(i) &lt;&lt; outMat;
  }
  filestorage &lt;&lt; "}";
  </code></pre>
  
  <p>And this is for loading:</p>
  
  <pre><code>FileNode k = n["ObjPoints"];
  int i = 0;
  for (FileNodeIterator it = k.begin(); it!=k.end(); ++it)
  {
      Mat inMat;
      k["ObjPoints_" + IntToString(i)] &gt;&gt; inMat;
      vector&lt;Point3f&gt; tmp = Mat_&lt;Point3f&gt;(inMat);
      ++i;
      objPoints.push_back(tmp);
  }
  </code></pre>
  
  <p>Where objPoints is a vector&lt; vector&lt; Point3f > > and IntToString is defined as follow:</p>
  
  <pre><code>string IntToString(int number)
  {
    stringstream ss;
    ss &lt;&lt; number;
    return ss.str();
  }
  </code></pre>
  
  <p>Can anyone point me in the right direction? Thanks.</p>