use opencv(2.4.13 C++)to access the bottom camera's video stream

[zxp771]

I'm trying to implement an visual odometry algorithm on the RTF drone(ubuntu16.04). I meet some problem when I try to access the bottom camera(global shutter) with Opencv API like this:

void BenchmarkNode::runFromFolder() {

cv::VideoCapture cap(2);  // open the default camera

if (!cap.isOpened())  // check if we succeeded
    return ;

int img_id = 0;
for (;;) {

    cv::Mat image;
    cap.read(image);  // get a new frame from camera

    assert(!image.empty());
    img_id++;

    cv::imshow("origin_image", image);
    if (cv::waitKey(1) >= 0) break;
    if(img_id < 100) continue;

    cv::cvtColor(image,image,CV_BGR2GRAY);
    /*
    cv::Mat unimg;
    cam_pinhole_->undistortImage(image,unimg);
    vo_->addImage(unimg, 0.01*img_id);
     */
    vo_->addImage(image, 0.01*img_id);

    // display tracking quality
    if(vo_->lastFrame() != NULL)
    {
        std::cout << "Frame-Id: " << vo_->lastFrame()->id_ << " \t"
                  << "#Features: " << vo_->lastNumObservations() << " \n";
        //<< "Proc. Time: " << vo_->lastProcessingTime()*1000 << "ms \n";
        std::cout<<"Frame pose: "<< vo_->lastFrame()->T_f_w_ <<std::endl;

    }

}

cap.release();
return;

}

but when I want to start the test it will occur this error: [INFO] SVO initialized HIGHGUI ERROR: libv4l unable to ioctl S_FMT Floating point exception (core dumped)

Here is the camera list. as the list shows I think the bottom camera should be 2.

I also tried to use: cv::VideoCapture cap; if(!cap.open("/dev/video2")) std::cout<<"camera error"<<std::endl; to get the video stream.but it will occur this error when i run the program.

GStreamer Plugin: Embedded video playback halted; module source reported: Could not read from resource. OpenCV Error: Unspecified error (GStreamer: unable to start pipeline ) in cvCaptureFromCAM_GStreamer, file /home/aero/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp, line 816 terminate called after throwing an instance of 'cv::Exception' what(): /home/aero/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp:816: error: (-2) GStreamer: unable to start pipeline in function cvCaptureFromCAM_GStreamer

Aborted (core dumped)

[zehortigoza]

It is /dev/video2 id=1, the id=1 is important. Please take a look at the aero-optical-flow code(V4L2), you can check how to open the camera using V4L2 APIs and then try to use other libraries that will call V4L2 APIs for you.

[zxp771]

@zehortigoza Hi Thanks for your help. Do you mean the /capturev4l2/capture.cpp?

[zehortigoza]

https://github.com/intel-aero/aero-optical-flow/blob/master/src/camera.cpp

[zxp771]

@zehortigoza Thanks for your help. Do I need install other libraries for V4L2?

[zehortigoza]

Not sure if your distro has, but you need the V4L2 headers to compile the application.

[zxp771]

@zehortigoza Thanks for your help. I will try these code but I'm not very familiar with V4L2. please do not close this issue very soon. Thanks