title: R rgl package error while loading the library
body: <p>My system environment:</p>
  <p>Mac OS 10.10.2</p>
  <p>X11 (XQuartz 2.7.5)</p>
  <p>R 3.1.2</p>
  <p>When I load and use 'rgl' package, I get following error message.</p>
  <pre><code>&gt; library(&quot;rgl&quot;,lib.loc=&quot;/Library/Frameworks/R.framework/Versions/3.1/Resources/library&quot;)
  Warning messages:
  1: In rgl.init(initValue, onlyNULL) : RGL: unable to open X11 display
  2: In fun(libname, pkgname) : error in rgl_init
  &gt; plot3d(x,y,z)
  Error in rgl.open(useNULL) : rgl.open failed
  </code></pre>
  <p>What's the problem?</p>