Explorer/RaspberryPi/Visualprocessing/Opencv

PIZero installation > 10h
PI3 installation > 4 hours

sudo apt-get install -y cmake
sudo apt-get install -y python-numpy python3-numpy libpython-dev libpython3-dev libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev libtiff-dev zlib1g-dev libjpeg-dev libpng-dev libavcodec-dev libavformat-dev libswscale-dev libv4l-dev libxvidcore-dev libx264-dev
sudo apt-get install libatlas-base-dev gfortran

for rasspberry pi3
sudo apt-get install libgtk2.0-dev

git clone https://github.com/opencv/opencv.git
git clone https://github.com/opencv/opencv_contrib.git 
cd ~/opencv 
git checkout 4.3.0
cd ~/opencv_contrib
git checkout 4.3.0

mkdir ~/opencv/build
cd ~/opencv/build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
   -D CMAKE_INSTALL_PREFIX=/usr/local \
   -D INSTALL_PYTHON_EXAMPLES=OFF \
   -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules \
   -D OPENCV_GENERATE_PKGCONFIG=YES \
   -D BUILD_TESTS=OFF \
   -D BUILD_PERF_TESTS=OFF \
   -D BUILD_EXAMPLES=OFF ..

=> GStreamer: YES (1.14.4)

/etc/dphys-swapfile
CONF_SWAPSIZE=2048

sudo /etc/init.d/dphys-swapfile stop
sudo /etc/init.d/dphys-swapfile start

make & 
for raspberrypi3: make -j4

sudo make install
sudo ldconfig -v