This repository is intended for development of "extra" modules that are contribution from the community, or that do not have stable API, that are not well-tested or that cannot be added to ViSP due to licensing. Thus, they shouldn't be released as a part of official ViSP distribution.
So, all the new modules should be developed separately, and published in the visp_contrib repository at first. Later, when the module matures, gains popularity and is compatible with ViSP licensing, it is moved to the central ViSP repository, and the development team provides production quality support for this module.
You can build ViSP, so it will include the modules from this repository. Here is the CMake command:
$ cd <parent_dir>
$ git clone https://github.com/lagadic/visp.git
$ git clone https://github.com/lagadic/visp_contrib.git
$ mkdir visp-build
$ cd visp-build
$ cmake -DVISP_CONTRIB_MODULES_PATH=../visp_contrib/modules ../visp
$ make -j4
As the result, ViSP will be built in the <parent_dir>/visp-build with all modules from visp and from visp_contrib repositories. If you don't want all of the modules, use CMake's BUILD_visp_* options. Like in this example:
$ cmake -DVISP_CONTRIB_MODULES_PATH=../visp_contrib/modules -DBUILD_visp_ar=OFF ../visp