Main Repo : Link OpenCV4 Repo : Link
Install Eigen 3.1 from Link Move Unziped Folder to /opt/. For build of Eigen read INSTALL file in folder.
Install v0.5 from Link
Resource Link
Download here : Link
Extract : unzip <file>.zip
sudo apt install python3-virtualenv
virtualenv opencvx
source opencvx/bin/activate
git clone https://github.com/opencv/opencv_contrib.git
mkdir build && cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D INSTALL_PYTHON_EXAMPLES=ON -D INSTALL_C_EXAMPLES=OFF -D OPENCV_EXTRA_MODULES_PATH=~/robo/opencv_contrib/modules -D PYTHON_EXECUTABLE=~/robo/opencvx/bin/python3 -D BUILD_EXAMPLES=ON ..
make -j8
sudo make install
sudo ldconfig