title: How to set a specific package path for CMakeLists.txt
body: <p>My colleague wrote a <code>CMakeLists.txt</code>, which contains things as below:</p>
  
  <pre><code>find_package(OpenCV 3 REQUIRED
    COMPONENTS
      opencv_core
      opencv_imgproc
      opencv_imgcodecs
    CONFIG
  )
  </code></pre>
  
  <p>As the project needs these components of Opencv3, my colleague downloaded the whole Opencv3, of course, it works.</p>
  
  <p>But the whole Opencv3 is too big, so I get only the necessary lib files: libopencv_core.so, libopencv_imgproc.so and libopencv_imgcodecs.so and try to replace the whole Opencv3. The three so files are put here: <code>/opt/opencv3/</code>.</p>
  
  <p>I don't know how to tell the CMakeLists.txt to look for the components of Opencv3 at the specific path instead of the path by default.</p>
  
  <p>I'm totally a newbie on writing CMakeLists.txt...</p>