my-ros2-cpp-alt-opencv

This repo shows how you can switch your ROS2 package to use a different version of OpenCV installed locally. See instruction for opencv installation at the end.

How to Compile the ROS2 package

First, put the source code tree directory inside your ROS2 workspace's src/ directory.

Option 1: Use system's OpenCV

rm -rf build/my-ros2-cpp-alt-opencv
colcon build --packages-select my-ros2-cpp-alt-opencv

Option 2: Use locally installed OpenCV

Modify CMakeLists.txt and replace the path below with your local opencv's installation directory.

  set(opencv3_install_dir "~/opencv3/install/")

Then, proceed to compile:

rm -rf build/my-ros2-cpp-alt-opencv
colcon build --packages-select my-ros2-cpp-alt-opencv --cmake-args -DUSE_ALT_OPENCV=1 

How to Run:

Option 1: Built with system's OpenCV

# source ROS 2 workspace environment
source install/setup.bash

# run the executable
ros2 run my-ros2-cpp-alt-opencv my_opencv

Option 2: Built with locally installed OpenCV

Make sure you change example below with your locally installed opencv directory.

# source ROS 2 workspace environment
source install/setup.bash

# run the executable with the LD_LIBRARY_PATH prefix.  Remember to
# replace "~/opencv3/install" with your local opencv installation directory.
LD_LIBRARY_PATH=~/opencv3/install/lib/:$LD_LIBRARY_PATH \
  ros2 run my-ros2-cpp-alt-opencv my_opencv

How to install OpenCV locally

First, download the source. In this example, we are building OpenCV 3.4.0.

mkdir ~/opencv3/
wget https://github.com/opencv/opencv/archive/3.4.0.zip
wget https://github.com/opencv/opencv_contrib/archive/3.4.0.zip
unzip opencv.zip
unzip opencv_contrib.zip
mv opencv-3.4.0 opencv
mv opencv_contrib-3.4.0 opencv_contrib

Then, compile:

mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
    -D CMAKE_INSTALL_PREFIX=~/opencv3/install \
    -D WITH_CUDA=OFF \
    -D INSTALL_PYTHON_EXAMPLES=OFF \
    -D OPENCV_EXTRA_MODULES_PATH=~/opencv3/opencv_contrib/modules \
    -D OPENCV_ENABLE_NONFREE=ON \
    -D WITH_QT=ON \
    -D WITH_GTK=OFF \
    -D WITH_OPENGL=ON \
    -D BUILD_EXAMPLES=ON \
    ../opencv/
make -j 4    # assume you have a 4-core CPU

You may encounter compilation errors due to the newer C++ compiler catching more code errors. Be sure to fix those error and continue. I had to fix a few places in the following files:

opencv_contrib/modules/stereo/src/descriptor.cpp
opencv/samples/cpp/cloning_gui.cpp
samples/cpp/tutorial_code/photo/seamless_cloning/cloning_gui.cpp
samples/cpp/tutorial_code/ImgProc/.../changing_contrast_brightness_image.cpp

Once everything builds, install the local opencv by:

make install

You should now see ~/opencv3/install/

ref: https://pyimagesearch.com/2018/05/28/ubuntu-18-04-how-to-install-opencv/