Getting started with rc_visard and OpenCV

This tutorial shows how to get started with the rc_visard and OpenCV. We will show how to receive image streams from the rc_visard with OpenCV via Roboception’s GenICam Convenience Layer rc_genicam_api.

Before we start

Before going through this tutorial, the following prerequisites should be met.

The rc_visard is up and running:

  1. The rc_visard is running and connected properly to a network or directly to a computer. One can verify that with our discovery tool.
  2. One should know the serial number or user defined name of the rc_visard. The serial number is of the format 029xxxxx. It will be referred to as rc_visard_id in the remainder of this tutorial.

Download and install the following required client software:

  1. Install rc_genicam_api. The minimum required version is 2.0.

  2. Install OpenCV. The minimum required version is 2.0.

    For Ubuntu, installation can be done from the terminal with:

    apt install libopencv-dev
    
  3. Install cmake. The minimum required version is 2.8.12.

    For Ubuntu, installation can be done from the terminal with:

    apt install cmake
    
  1. Download rc_genicam_api

  2. Install OpenCV. The minimum required version is 2.0.

    Pre-built binaries can be downloaded here.

  3. Install cmake. The minimum required version is 2.8.12.

  4. Install Microsoft Visual Studio-IDE

Compiling the example program

We provide an example program which shows how to receive image streams from the rc_visard using rc_genicam_api and how to convert them to an OpenCV representation. The example can be downloaded from our GitHub repository.

To successfully compile the program, above prerequisites should be met.

After downloading or cloning the repository, change into the repository’s directory. In a terminal, run the following commands:

mkdir build    # make a build directory
cd build       # change to that directory
cmake ..       # run cmake to configure the build
make           # build the example
  1. Create a folder build in the repository.
  2. Run CMake (cmake-gui)
  3. In cmake, set the source code location to the repository folder
  4. Set the binaries location to the just created build folder
  5. Click Configure
  6. A pop-up will open, asking for the generator
  7. Choose the installed version of Visual Studio
  8. Click finish
  9. Wait until configuration is finished
  10. Most likely, an error about not finding OpenCV will occur
    1. Set OpenCV_DIR to the subfolder build\x64\vc15\lib of the OpenCV installation path
    2. Again, click Configure
  11. Most likely, an error about not finding rc_genicam_api will occur
    1. Set RC_GENICAM_API_DIR to the subfolder lib\rc_genicam_api of the rc_genicam_api installation path
    2. Again, click Configure
  12. Set CMAKE_INSTALL_PREFIX to the folder where the example is installed (e.g. install in the repository)
  13. Click Generate
  14. Click Open Project. Microsoft Visual Studio-IDE will open
  15. In Visual Studio, right-click on ALL_BUILD and choose Build
  16. Right-click on INSTALL and choose Build

The build will yield a shared library (rc_visard_opencv_example) and an executable (rc_visard_show_streams), which uses the shared library.

Running the example program

The example executable rc_visard_show_streams shows live image streams in an OpenCV window. One can specify which streams to enable by setting command line options.

In case above build instructions were used, one should first change to the tools directory in build before running the program:

cd tools

To run the program, the general syntax is:

./rc_visard_show_streams [options] <rc_visard_id>

In the following we assume that above build instructions were followed and that the example program was installed into install in the repository folder.

  1. Open the install folder

  2. In the address bar of the Windows Explorer window, type cmd to open a command line window

  3. To run the program, use the following command

    rc_visard_show_streams.exe [options] <rc_visard_id>
    

Note

The PATH environment variable should be set to the appropriate folders containing the OpenCV and rc_genicam_api DLLs. Otherwise, an error will occur when running rc_visard_show_streams.

<rc_visard_id> is to be replaced by the rc_visard serial number, GenTL ID or user defined ID.

[options] can be

  • --left: connect to the left image stream
  • --right: connect to the right image stream
  • --disparity: connect to the disparity image stream
  • --confidence: connect to the confidence image stream
  • --error: connect to the error image stream
  • --synchronize: synchronize the received images by their timestamp

For example, to show the left and right image, run:

./rc_visard_show_streams --left --right <rc_visard_id>
rc_visard_show_streams.exe --left --right <rc_visard_id>

While the program is running, press n (next), p (previous) to cycle through the enabled image streams. Press q to exit the program.

Explanation of the example’s source code

The example is documented using Doxygen. To generate the source code documentation, perform the following steps:

In the build directory, run:

make doc

Afterwards, open index.html in doc/html.

  1. Install Doxygen
  2. In the cmake-gui, click on Configure and then Generate
  3. Click on Open Project
  4. In Microsoft Visual Studio-IDE, right-click on doc and choose BUILD
  5. Go to the build\doc\html subfolder of the repository
  6. Open index.html

Project structure

digraph dependencies {
   rankdir=BT;
   splines=ortho;
   node [shape=record,
         style=filled,
         fillcolor=gray95,
         fontname=Consolas,
         fontsize=10];
   rcgenapi [label="rc_genicam_api"];
   opencv [label="OpenCV"];
   lib [label="rc_visard_opencv_example"];
   exe [label="rc_visard_show_streams"];
   exe -> lib;
   exe -> opencv;
   lib -> opencv;
   lib -> rcgenapi;
}

Fig. 9 Dependency diagram

The example consists of a shared library rc_visard_opencv_example and an executable rc_visard_show_streams. The library is designed to make it easy to reuse it for other projects that require OpenCV images. Below, the library will be described in more detail.

Both the library and the executable depend on OpenCV. rc_genicam_api is hidden by the shared library rc_visard_opencv_example.

Library structure

digraph class {
   node [shape=record,
         style=filled,
         fillcolor=gray95,
         fontname=Consolas,
         fontsize=10];

   gcreceiver [label="{GcReceiver|GcReceiver(string device_id)\lopen()\linitializeStreams(list\<ImageReceiverFactory\>)\lreceive(...): ImageSet\l...}"];
   imagereceiver [label="{ImageReceiver|process(...): bool\l...}"];
   imagereceiverfactory [label="{ImageReceiverFactory|enableAndMake(...): ImageReceiver\l...}"];
   image [label="Image"];
   imageset [label="ImageSet"];

   imagereceiver -> gcreceiver [arrowhead=diamond];

   image -> imageset [arrowhead=odiamond];
}

Fig. 10 Simplified class diagram

The core class of rc_visard_opencv_example is GcReceiver. It wraps rc_genicam_api, takes care of bootstrapping and shutting down the connection to the rc_visard, and delegates decoding of image streams to the appropriate ImageReceiver.

ImageReceiver is an abstract base class of the concrete classes IntensityReceiver, DisparityReceiver, ConfidenceReceiver and ErrorReceiver, each of which is responsible for receiving one kind of image stream. Each concrete ImageReceiver implements a) enabling of the image stream from the rc_visard and b) converting the GenICam representation of the image to an OpenCV representation.

The user of the library decides which image streams to enable by passing a list of ImageReceiverFactorys to GcReceiver. For each concrete ImageReceiver there is child class of ImageReceiverFactory, e.g. IntensityReceiverFactory.

To set up streaming of images, the following steps are required:

  1. Create a new GcReceiver. Its constructor requires the rc_visard_id.
  2. Call GcReceiver::open() to open the connection to the rc_visard.
  3. Call GcReceiver::initializeStreams() and pass the list of ImageReceiverFactorys.

After set-up was successful, we can start receiving images. For that, GcReceiver::receive() needs to be called. It grabs the latest image from the GenICam buffer and passes it to each ImageReceiver via its process() method, until one of them takes responsibility for it. The image buffer is then stored in a queue in the ImageReceiver. Afterwards, the image can be extracted from the queue and converted to an OpenCV representation by calling ImageReceiver::grab() and passing the timestamp of the image. This all happens inside GcReceiver::receive(), so the user does not need to care about it. receive() will return an ImageSet with all received images contained.

ImageSet is an aggregation of Images, one for each image type, including left, right, confidence, disparity and error image. Depending on whether synchronization is enabled (see command line options), the returned ImageSet either contains a complete set of synchronized images or only the one image that was just received.

Enabling image streams

To get some insights into the internal working of rc_visard_opencv_example, this and the following section will explain how image streams are enabled and how the GenICam representation of images is converted to OpenCV.

Before enabling image streams, the connection to the rc_visard needs to be set up.

// Implemented in gc_receiver.cc

std::string rc_visard_id = "rc_visard";
// search for the device
std::shared_ptr<rcg::Device> device = rcg::getDevice(rc_visard_id.c_str());
// open the connection
device->open(rcg::Device::CONTROL);

The following code exemplarily shows how to enable streaming of the intensity image, which contains the left camera image.

// Implemented in gc_receiver.cc and image_receiver.cc

// get the node map
std::shared_ptr<GenApi::CNodeMapRef> node_map = device->getRemoteNodeMap();
// select the component "Intensity"
rcg::setEnum(node_map, "ComponentSelector", "Intensity");
// enable the selected component
rcg::setBoolean(node_map, "ComponentEnable", true);

// start streaming
std::vector<std::shared_ptr<Stream>> streams = device->getStreams();
streams[0]->open();
streams[0]->startStreaming();

Converting GenICam images to OpenCV

Depending on the image type, there is a different conversion required to get from the GenICam representation to the OpenCV representation of an image. Here, we will show the simple example of converting the GenICam monochrome intensity stream to an OpenCV cv::Mat. For the other conversions, please refer to image_receiver.cc in the repository.

The queue in ImageReceiver provides images of type rcg::Image. Internally, the image data is stored in a contiguous block of memory in an eight bit representation, so each byte represents one monochrome pixel. Since cv::Mat uses the same eight bit representation, we don’t need any byte-to-byte conversion.

Yet, a simple copy of the memory block of rcg::Image into a cv::Mat is not ideal because rcg::Image may contain padding bytes appended to each image row. Therefore, we copy each row separately, while skipping the padding bytes, in order to generate a continuous cv::Mat.

// Implemented in image_receiver.cc

cv::Mat convert(const rcg::Image &buffer)
{
  const int width = static_cast<int>(buffer.getWidth());
  const int height = static_cast<int>(buffer.getHeight());

  cv::Mat img(height, width, CV_8UC1);
  // width of a row in the GenICam buffer including padding
  const int buffer_step = width + static_cast<int>(buffer.getXPadding());
  // data start pointer
  const uint8_t *buffer_row_ptr = buffer.getPixels();
  // iterate image rows
  for (int row_idx = 0; row_idx < height; ++row_idx)
  {
    uint8_t *const img_row = img.ptr<uint8_t>(row_idx);
    // plain byte-wise copy of one row from the buffer to the cv::Mat
    std::copy(buffer_row_ptr, buffer_row_ptr + width, img_row);
    buffer_row_ptr += buffer_step;
  }
  return img;
}