title: CGAL Error: Eigen3 is required -> Eigen seems to be okay though
body: <p>When running my program with this CGAL include for example:</p>
  
  <pre><code>#include &lt;CGAL/Epick_d.h&gt;
  </code></pre>
  
  <p>I get two error messages that read:</p>
  
  <pre><code>C1189 #error: Eigen3 is required 
  </code></pre>
  
  <p>and</p>
  
  <pre><code>#error directive: Requires Eigen
  </code></pre>
  
  <p>They direct to cartesian_la_base.h and constructors.h respectively.
  There I find the following piece of code:</p>
  
  <pre><code>#ifndef CGAL_EIGEN3_ENABLED 
  #error Requires Eigen
  #endif
  </code></pre>
  
  <p>So it seems to me that the CGAL_EIGEN3_ENABLED flag is not set. I cannot find a problem with either CGAL or Eigen though, so I am a bit puzzled as to why this is happening.
  I set an environment variable to .../Eigen and included the directory under Properties -> c/c++ -> General -> Additional Include Directories as well as
  in Linker -> General. </p>
  
  <p>Strangely enough, there seems to be virtually no-one else to receive the same error-message, judging from my success with googling the matter.</p>
  
  <p>I use Visual Studio 2015.</p>
  
  <p>Hopefully this is enough information.
  Cheers</p>