使用cmake find_package找不到opencv

对cmake的使用不是很熟悉，遇到这个问题为自己简单记录一下。
错误如下：
CMake Error at CMakeLists.txt:39 (find_package):
  By not providing "FindOpenCV.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "OpenCV", but
  CMake did not find one.

  Could not find a package configuration file provided by "OpenCV" with any
  of the following names:

    OpenCVConfig.cmake
    opencv-config.cmake

  Add the installation prefix of "OpenCV" to CMAKE_PREFIX_PATH or set
  "OpenCV_DIR" to a directory containing one of the above files.  If "OpenCV"
  provides a separate development package or SDK, be sure it has been
  installed.
原因：由于我安装opencv时，不是使用的默认的路径，导致cmake找不到opencv
解决方法：
首先    export OpenCV_DIR=/usr/local/opencv-3.1.0
然后在build目录下执行  cmake  ..  即可