Cmake searches for opencv library - opencv

Question

I have installed Opencv-3.2 and I can see the bin and lib files
$ ls /share/apps/computer/opencv-3.2.0/built/bin/opencv_
opencv_annotation opencv_createsamples opencv_traincascade opencv_version opencv_visualisation
$ ls /share/apps/computer/opencv-3.2.0/built/lib/
libopencv_calib3d.so libopencv_imgcodecs.so.3.2.0 libopencv_stitching.so.3.2
libopencv_calib3d.so.3.2 libopencv_imgproc.so libopencv_stitching.so.3.2.0
libopencv_calib3d.so.3.2.0 libopencv_imgproc.so.3.2 libopencv_superres.so
libopencv_core.so libopencv_imgproc.so.3.2.0 libopencv_superres.so.3.2
libopencv_core.so.3.2 libopencv_ml.so libopencv_superres.so.3.2.0
libopencv_core.so.3.2.0 libopencv_ml.so.3.2 libopencv_videoio.so
libopencv_features2d.so libopencv_ml.so.3.2.0 libopencv_videoio.so.3.2
libopencv_features2d.so.3.2 libopencv_objdetect.so libopencv_videoio.so.3.2.0
libopencv_features2d.so.3.2.0 libopencv_objdetect.so.3.2 libopencv_video.so
libopencv_flann.so libopencv_objdetect.so.3.2.0 libopencv_video.so.3.2
libopencv_flann.so.3.2 libopencv_photo.so libopencv_video.so.3.2.0
libopencv_flann.so.3.2.0 libopencv_photo.so.3.2 libopencv_videostab.so
libopencv_highgui.so libopencv_photo.so.3.2.0 libopencv_videostab.so.3.2
libopencv_highgui.so.3.2 libopencv_shape.so libopencv_videostab.so.3.2.0
libopencv_highgui.so.3.2.0 libopencv_shape.so.3.2 pkgconfig/
libopencv_imgcodecs.so libopencv_shape.so.3.2.0
libopencv_imgcodecs.so.3.2 libopencv_stitching.so
Now, according to the tutorial, I wrote a simple program. Problem is that, cmake gets some errors and seems that it is not able to find the library.
CMake Error at CMakeLists.txt:3 (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.
I don't know how to set CMAKE_PREFIX_PATH or OpenCV_DIR. How can I fix that?
The content of CMakeLists.txt is
cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED )
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )

Answer 1

It depends whether you have OpenCVConfig.cmake script, which comes with your installation of OpenCV (that is, under install directory /share/apps/computer/opencv-3.2.0/built/).
If your installation of OpenCV lacks of OpenCVConfig.cmake script, you need to ship your project with script FindOpenCV.cmake (find and copy it from the net, almost any of them is suitable), and add directory with this script to CMAKE_MODULE_PATH variable:
list(APPEND CMAKE_MODULE_PATH <directory-with-find-script>)
Possible ways to hint CMake about your installation of OpenCV:
If you have OpenCVConfig.cmake script, set OpenCV_DIR variable to directory contained this script:
cmake -DOpenCV_DIR=/share/apps/computer/opencv-3.2.0/built/<...>
Set CMAKE_PREFIX_PATH variable to installation prefix of OpenCV:
cmake -DCMAKE_PREFIX_PATH=/share/apps/computer/opencv-3.2.0/built
This works both with OpenCVConfig.cmake and with FindOpenCV.cmake scripts. See also that question: Hinting Find<name>.cmake Files with a custom directory.