opencv raspberry pi

#https://www.pyimagesearch.com/2016/04/18/install-guide-raspberry-pi-3-raspbian-jessie-opencv-3/
sudo raspi-config  #use all of the SD card.

sudo apt purge wolfram-engine  #and libreoffice

sudo apt install     -y build-essential git cmake pkg-config
sudo apt update; sudo apt-get upgrade; sudo rpi-update
sudo apt-get         -y install python2.7-dev python3-dev
sudo apt install     -y libjpeg-dev libtiff5-dev libjasper-dev libpng12-dev
sudo apt-get install -y  libavcodec-dev libavformat-dev libswscale-dev libv4l-dev
sudo apt-get install -y libxvidcore-dev libx264-dev
sudo apt-get install -y libgtk2.0-dev
sudo apt-get install -y libatlas-base-dev gfortran
wget https://bootstrap.pypa.io/get-pip.py
sudo python get-pip.py
pip install numpy

cd ~
#### do github clone here rather.
#wget -O opencv.zip https://github.com/Itseez/opencv/archive/3.3.0.zip
#unzip opencv.zip

wget -O opencv_contrib.zip https://github.com/Itseez/opencv_contrib/archive/3.3.0.zip
unzip opencv_contrib.zip

cd /etc/dphys-swapfile
# set size to absolute value, leaving empty (default) then uses computed value
#  you most likely don't want this, unless you have an special disk situation
# CONF_SWAPSIZE=100
# https://www.bitpi.co/2015/02/11/how-to-change-raspberry-pis-swapfile-size-on-rasbian/
CONF_SWAPSIZE=1024

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

cd ~/opencv-3.3.0/
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
    -D CMAKE_INSTALL_PREFIX=/usr/local \
    -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib-3.3.0/modules \
    -D ENABLE_NEON=ON \
    -D ENABLE_VFPV3=ON \
    -D BUILD_TESTS=OFF \
    -D INSTALL_PYTHON_EXAMPLES=ON \
    -D BUILD_EXAMPLES=ON ..
make -j4; sudo make install; sudo ldconfig
#go back to swap file reset to 100mb!


#https://www.pyimagesearch.com/2016/04/18/install-guide-raspberry-pi-3-raspbian-jessie-opencv-3/
# make certain that cv2.so in site packages are in both python2 and 3 . See web for details.