CMake Error at cmake/OpenCVModule.cmake:295 (message): No extra modules found in folder:Please provide path to 'opencv_contrib/modules' folder

其实，我们使用的opencv中要用的contrib/modules   是需要额外下载并在cmakelists.txt中指定的

     git clone https://github.com/opencv/opencv_contrib.git
  然后，就有opencv_contrib  的path啦

cd opencv_contrib
git checkout 3.1.0   别忘了check你的版本