opencv_catkin

Catkin wrapper for opencv (originally by ASL at ETH)

Getting started

Configuration

• All the desired configuration must be manually set in the CMakeLists.txt file. Please read carefully the comments depending on what you need.
• OpenCV's version is implicitley chosen via the zip url in lines 14 and 30. It must be obtained from the release page in the official GitHub repo.
• The version of (opencv_contrib) must match opencv's and, similarly, can be obtained from here.
• ROS version considerations: if you plan to use it with ROS Melodic, you must use OpenCV 3.2; for Noetic you need OpenCV 4.2. Otherwise you'll have linking errors because of the mismatch between the system libraries and this package (and that will require that you also build your own versions of other ROS packages, e.g. cv_bridge, which could also fail depending on the version of OpenCV you are trying to use).
• Please note that not all the options that OpenCV offers are available in the CmakeLists.txt file in this package. Confirm with the original OpenCV's CMakeLists.
• If you want to use cmake-gui or ccmake to change the setup, you can open them in ~/catkin_ws/build/opencv_catkin/opencv_opencv_build

Compilation

Normal compilation

This should be straightforward on your desktop machine:

catkin build opencv_catkin

Compilation with CUDA support

In order to make the process faster and avoid compiling code for all the possible CUDA architectures, you can manually select the compute capability (CUDA_ARCH_BIN) of your board. Check here for the full list.

For example, to compile on a Xavier board (CUDA_ARCH_BIN=7.2) you will use:

catkin build opencv_catkin --cmake-args -DCUDA_ARCH_BIN=7.2

Other video cards such as the Nvidia Quadro P200 (CUDA_ARCH_BIN=6.1) additionally require to use an older version of GCC. You can set it manually:

catkin build opencv_catkin --cmake-args -DCUDA_ARCH_BIN=6.1 -DCMAKE_C_COMPILER=/usr/bin/gcc-7

Other notes

Changing OpenCV's source

• If you want to change the source (to include some messages, changing some implementations, etc), the source code is available in ~/catkin_ws/build/opencv_catkin/opencv_src
• Similarly, opencv_contrib modules can be found in ~/catkin_ws/build/opencv_catkin/opencv_contrib_src

Check that the libraries are correctly linked

Catkin will automatically find OpenCV (as usual, with CMake), in the devel folder. You only have to compile this package first, and then the package that depends on OpenCV. If you have already built your package, you must clean it up and build again, otherwise your package will stay linked to the system libraries.

If you want to confirm that you are linking your package to the right libraries:

• Go to ~/catkin_ws/devel/lib.
• You should find the OpenCV binary libraries libopencv_*.so
• You should also find your package. For example, libmypackage.so
• To check which libraries mypackage is linked to, use ldd libmypackage.so. THey should point to the OpenCV's binaries found before.