title: Combining multiple transformations in Eigen into one transformation matrix
body: <p>I have several transformations in Eigen, in the form of translations (<code>Eigen::Vector3f</code>) and rotations (<code>Eigen::Quaternionf</code>). I would like to combine all these transformations, in an order of my choosing, into a 4x4 transformation matrix <code>Eigen::Matrix4f</code>.</p>
  
  <p>For example, I would like to apply the following transformations in the order A, B, C, D, E:</p>
  
  <pre><code>Eigen::Vector3f translation_A;
  Eigen::Quaternionf rotation_B;
  Eigen::Quaternionf rotation_C;
  Eigen::Quaternionf rotation_D;
  Eigen::Vector3f translation_E;
  </code></pre>
  
  <p>What is the simplest way of achieving this? I have so far been applying them individually to my final data like so:</p>
  
  <pre><code>pcl::transformPointCloud(*cloud_in, *cloud_out, translation_A, IDENTITY_QUATERNION);
  pcl::transformPointCloud(*cloud_out, *cloud_out, ZERO_TRANSLATION, rotation_B);
  pcl::transformPointCloud(*cloud_out, *cloud_out, ZERO_TRANSLATION, rotation_C);
  pcl::transformPointCloud(*cloud_out, *cloud_out, ZERO_TRANSLATION, rotation_D);
  pcl::transformPointCloud(*cloud_out, *cloud_out, translation_E, IDENTITY_QUATERNION);
  </code></pre>
  
  <p>...but there must be a simple (built-in?) way of combining these transformations using Eigen, into a final 4x4 transformation matrix. </p>