How to build opencv_contrib module for iOS

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The README file of the OpenCV contrib Github page has the complete explanation on how to do so. It involves adding a CMAKE command to the list pointing out the contribution modules.

You can build OpenCV, so it will include the modules from this repository. Here is the CMake command for you:

$ cd <opencv_build_directory>
$ cmake -DOPENCV_EXTRA_MODULES_PATH=<opencv_contrib>/modules <opencv_source_directory>
$ make -j5

As the result, OpenCV will be built in the <opencv_build_directory> with all modules from opencv_contrib repository. If you don't want all of the modules, use CMake's BUILD_opencv_* options. Like in this example:

$ cmake -DOPENCV_EXTRA_MODULES_PATH=<opencv_contrib>/modules -DBUILD_opencv_legacy=OFF <opencv_source_directory>

If you prefer using the gui version of cmake (cmake-gui), then, you can add opencv_contrib modules within opencv core by doing the following:

1. start cmake-gui
2. select the opencv source code folder and the folder where binaries will be built (the 2 upper forms of the interface)
3. press the configure button. you will see all the opencv build parameters in the central interface
4. browse the parameters and look for the form called OPENCV_EXTRA_MODULES_PATH (use the search form to focus rapidly on it)
5. complete this OPENCV_EXTRA_MODULES_PATH by the proper pathname to the <opencv_contrib>/modules value using its browse button.
6. press the configure button followed by the generate button (the first time, you will be asked which makefile style to use)
7. build the opencv core with the method you chose (make and make install if you chose Unix makfile at step 6)