title: How can I prevent homebrew from upgrading VTK dependency for PCL?
body: <p>I would like to install the <code>pcl</code> formula through homebrew, which is documented here:
  <a href="http://www.pointclouds.org/documentation/tutorials/installing_homebrew.php" rel="nofollow">http://www.pointclouds.org/documentation/tutorials/installing_homebrew.php</a></p>
  
  <p>Unfortunately, homebrew decides it needs to upgrade my <code>VTK</code> installation to the latest release (6.0) even though I have a perfectly working version (5.10.1) installed already. I would like to compile against and link with this existing version. (The minimum <code>VTK</code> version for <code>pcl</code> is listed as 5.6.1, so everything should work fine. I actually manually build <code>pcl</code> and tried to link it against VTK 6.0, which doesn't even work, yet.) </p>
  
  <p>Therefore, my question is, why does homebrew try to upgrade VTK (to an incompatible version) and how can I prevent it from doing this?</p>
  
  <p>All I am calling is: <code>brew install pcl</code>, which triggers this:</p>
  
  <pre><code>==&gt; Installing pcl dependency: vtk
  ==&gt; Downloading http://www.vtk.org/files/release/6.0/vtk-6.0.0.tar.gz
  Already downloaded: /Library/Caches/Homebrew/vtk-6.0.0.tar.gz
  </code></pre>
  
  <p>This eventually leads to an error, as vtk 6.0 does not compile under Mac OS X 10.9 through homebrew (<a href="https://github.com/Homebrew/homebrew-science/issues/401" rel="nofollow">https://github.com/Homebrew/homebrew-science/issues/401</a>).</p>
  
  <p>To be clear, even if VTK 6.0 would compile fine, I do not want to upgrade, so does anyone know how to prevent homebrew from upgrading a dependent formula?</p>