OpenCV2OpenGL

Minimal working examples for converting OpenCV cameras to OpenGL cameras, render, and save as Mat images in OpenCV.

These examples have a MIT license and are created by Amy Tabb as a companion to a tutorial series, at amytabb.com.

There are no restrictions in your use of this code. However, no guarantees are expressed or implied.

Dependencies

This code uses >= OpenCV 3.0, Eigen, OpenGL, glad, glfw3, glm, and has been tested on Ubuntu 16.04 and Ubuntu 18.04. An Eclipse project file as well as cmake option are included.

1. OpenCV While OpenCV is available from distribution repositories, my long experience with it is has always been to build from the source (from Github) to get the best results. I have used OpenCV 4.x, which requires a >= C++11 compiler. I enable the GNU version with a flag : -std=gnu++11. There other ways of doing this, as well as other choices of compiler. OpenCV 3.x should work fine (but has not been tested ...) Required libraries are: opencv_core, opencv_highgui, opencv_imgproc, opencv_imgcodecs .

2. Check the include directory for Eigen, Eigen is a header-only library.

3. Installation of glfw3 and glad are covered at this page of LearnOpenGL. For glad, files are downloaded according to your specifications. The files I have included are for OpenGL 3.3, which is old enough to cover many systems. The files for Example1 are in Example1->include, so you can either try to use the ones provided, or download your own, and specify the include path.

4. GLM is another header-only library, and can be found here, I tend to install everything from the source (versus the distribution repositories), but libglm-dev is also avaliable there from Ubuntu for a no-hassle installation.

5. Linking: link with these libraries: -lglfw3 -lGLU -lglut -lm -lGL -lpthread -ldl -lrt -lX11 -lXrandr -lopencv_core -lopencv_imgproc -lopencv_imgcodecs -lopencv_highgui

6. At the moment there is only Example1, but these are Eclipse IDE projects. If you use Eclipse, you can import the project and alter the include paths from there.

Building with Eclipse

Eclipse .project and .cproject files are included, but these are hidden files within Example1. Import to the Eclipse IDE and you might need to edit some of the include paths.

Building with CMake

1. Assuming that you can cloned, from the command line, https://github.com/amy-tabb/OpenCV2OpenGL.git

2. cd OpenCV2OpenGL/Example1

3. The code is in src. Create a build directory, mkdir build , cd build.

4. Here's the cmake fun. The version of OpenCV shouldn't matter too much, a semi-modern version > 2 should be fine. I don't specify a version in the src/CMakeLists.txt file. However, you can specify which version of OpenCV is used by altering the the find_package() line:

• find_package( OpenCV 3.4.8 REQUIRED )
• find_package( OpenCV 4 REQUIRED )

5. Configure with cmake. Don't have cmake? (sudo apt-get install cmake). Then from the build folder, you can use any of the following four options below:

• cmake ../src (basic)
• cmake -DCMAKE_BUILD_TYPE=Release ../src (Release configuration)
• cmake -DCMAKE_BUILD_TYPE=Debug ../src (Debug configuration)
• cmake -G"Eclipse CDT4 - Unix Makefiles" -DCMAKE_ECLIPSE_GENERATE_SOURCE_PROJECT=TRUE ../src/ (Create an Eclipse project to import -- it will be in the build folder)

In case you have installed OpenCV and cmake can't find it, you need to specify the location of OpenCVConfig.cmake. Don't know where it is? Find out with locate OpenCVConfig.cmake. Then append

-DCMAKE_PREFIX_PATH=dir

in my case on one machine, this was:

-DCMAKE_PREFIX_PATH=/usr/local/opencv41/lib/cmake/opencv4/

where /usr/local/opencv41/lib/cmake/opencv4/ is the directory containing OpenCVConfig.cmake. Of course, you will substitute whatever the appropriate directory returned from locate OpenCVConfig.cmake was.

6. Then, you can either import the project to Eclipse (if you used the last option), or build from there, or type make. If the everything compiled and linked, and you have an executable named opencv2opengl, you are ready to go.

Running

For help, run with --help.

Otherwise, each example will take different arguments and this repository will change over time. Refer to the website for samples or run --help to find out arguments for each example.

Model source

The horse model is from the Georgia Tech Large Model Archive. The number of triangles was reduced, and color was introduced by me, by playing around in Meshlab.

3D model viewer

There are many 3D model viewers out there, I use Meshlab, which is free.