Human detection

This tutorial assumes that RAPP API and OpenCV are installed.

We are going to create a project using OpenCV, RAPP API and CMake.

Using CMake requires you to configure your CMakeLists.txt in the root of your RAPP project. Essentially, the structure is the following:


Source code

We created a project called human_detection with a folder source where we have our example call human_detection.cpp. You can see the complete example here.

In this example we are going to take images from a camera and we are going to use this image to call the RAPP platform and look for humans.

For taking a image from our usb camera we have to use OpenCV:

cv::VideoCapture camera(0); 
if(!camera.isOpened()) { 
    std::cout << "Failed to connect to the camera" << std::endl;
    return -1;

We created the parameter camera which is our dev0. You will have to check if your camera is in the correct device and change the number if it's necessary. In the case that the program don't recognise any devices, the program will close.

If you want to change the resolution of the image from your camera, you only have to change the parameters of the camera. You have to remember that the bigger the image is, more time is going to take to analize the image.


In other examples, we only see the result with a stdout. Now we would like to see the position of the humans in the image that our camera is recording. So, we are going to create an OpenCV window:

cv::namedWindow("Human detection", cv::WINDOW_AUTOSIZE);

The size of the window depends of your camera resolution. At the same time, we can initialize our OpenCV matrix where we are going to save the image data from the camera:

cv::Mat frame;

At this point, we can continue our program like RAPP API examples. We are going to initialize the platform information and the service controller, which is in charge of make the cloud calls to the RAPP platform:

rapp::cloud::platform info = {"", "9001", "rapp_token"}; 
rapp::cloud::service_controller ctrl(info);

One the parts that it's needed to make the human_detection call is to send a callback, so we are going to do one before the for loop because we don't need to create it in every loop:

auto callback = [&](std::vector<rapp::object::human> humans) { 
    std::cout << "Found: " << humans.size() << " humans" << std::endl; 
    for(auto each_human : humans) {
                      cv::Point(each_human.get_left_x(), each_human.get_left_y()),
                      cv::Point(each_human.get_right_x(), each_human.get_right_x()),
                      1, 8, 0);

This callback shows how many humans have been found and, if there is any, it draws a blue rectangle in the image where the human is.

Before writing the for loop we have to keep in mind that we can't use a simple loop to make the calls because we can block the platform if we don't stop sending calls. Because of that we have the example rapp-api/cpp/examples/loop.cpp, where wait a second for doing a call. However, we have the problem that loop.cpp example can't be use with the window interhuman of OpenCV. So, in the case we want to use the OpenCV interhuman, we are going to use a std::chrono object which is going to count the time between loops. In this example, we are going to make a call every 500 ms.

auto before = std::chrono::system_clock::now();
for (;;) {
    auto now = std::chrono::system_clock::now();
    auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - before).count(); 

Another issue that we can find is to create a picture object, which we need it to make the human_detection call, because to create one it's needed a ifstream. This means, that cv::Mat we have to convert it in a correct way. The good news is OpenCV has a function which is perfect for this cv::imencode.

To see more information, you can visit this web page: cv::imencode.

Then, every 500 ms we have to pass the parameter in this way:

if (elapsed > 500) {
    camera >> frame;

    std::vector<int> param = {{ CV_IMWRITE_PNG_COMPRESSION, 3 }};
    cv::vector<uchar> buf;
    cv::imencode(".png", frame, buf, param);
    std::vector<rapp::types::byte> bytes(buf.begin(), buf.end());
    auto pic = rapp::object::picture(bytes);

    before = now;
    ctrl.make_call<rapp::cloud::human_detection>(pic, callback);
    cv::imshow("Human detection", frame);

After having the picture object, we can make the call and then show in the OpenCV interhuman (cv::imshow). However, the interhuman is not going to refresh the image until we use cv::waitKey function. To see more information you can visit this web site: OpenCV interhuman.

NOTE: You'll have to add the propers headers at the begining of the file. If you have some doubts, you can see the complete example link above


In this case it assumes that you have built your RAPP API in the static and shared libraries mode.

This file is going to be the same that we have in helloworld/CMakeLists.txt file. We only have to add the OpenCV library and change the names of the project and executable.

NOTE: If you want to use only the static libraries, you can see helloworld_static project.

Then, the only lines that we have to add are:

find_package(OpenCV REQUIRED)


target_link_libraries(human_detection ${RAPP_LIBRARIES}

And modify the names of the executable and the project:


add_executable(human_detection source/human_detection)

Repository detail

Before to do anything we have to be careful in the case that we are using a repository. If you are not using with your project, then ignore this part. In the case you are using one with Github, you will have to create a file call .gitignore (inside your project directory) where you only write this:


This means that you are not going to save this folder in the repository. It is good to do it because in the case you shared your project, the other person won't have problems building it. It's a specific folder for every user.

Building your code

The next step is about create our build folder and run our code.

Now we are going to work in the terminal.

  1. Go to your project path (in our case human_detection/)
  2. Build your project

    mkdir build
    cd build 
    cmake ..
  3. If everything is ok, you will have created your executable human_detection in the folder build.
  4. Run your executable

Now you can explore and make your own projects!