samples/cpp/polar_transforms.cpp

An example using the cv::linearPolar and cv::logPolar operations

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>

using namespace cv;

static void help( void )
{
    printf("\nThis program illustrates Linear-Polar and Log-Polar image transforms\n"
            "Usage :\n"
            "./polar_transforms [[camera number -- Default 0],[path_to_filename]]\n\n");
}

int main( int argc, char** argv )
{
    VideoCapture capture;
    Mat log_polar_img, lin_polar_img, recovered_log_polar, recovered_lin_polar_img;

    help();

    CommandLineParser parser(argc, argv, "{@input|0|}");
    std::string arg = parser.get<std::string>("@input");

    if( arg.size() == 1 && isdigit(arg[0]) )
        capture.open( arg[0] - '0' );
    else
        capture.open(samples::findFileOrKeep(arg));

    if( !capture.isOpened() )
    {
        const char* name = argv[0];
        fprintf(stderr,"Could not initialize capturing...\n");
        fprintf(stderr,"Usage: %s <CAMERA_NUMBER>    , or \n       %s <VIDEO_FILE>\n", name, name);
        return -1;
    }

    namedWindow( "Linear-Polar", WINDOW_AUTOSIZE );
    namedWindow( "Log-Polar", WINDOW_AUTOSIZE);
    namedWindow( "Recovered Linear-Polar", WINDOW_AUTOSIZE);
    namedWindow( "Recovered Log-Polar", WINDOW_AUTOSIZE);

    moveWindow( "Linear-Polar", 20,20 );
    moveWindow( "Log-Polar", 700,20 );
    moveWindow( "Recovered Linear-Polar", 20, 350 );
    moveWindow( "Recovered Log-Polar", 700, 350 );
    int flags = INTER_LINEAR + WARP_FILL_OUTLIERS;
    Mat src;
    for(;;)
    {
        capture >> src;

        if(src.empty() )
            break;

        Point2f center( (float)src.cols / 2, (float)src.rows / 2 );
        double maxRadius = 0.7*min(center.y, center.x);

#if 0 //deprecated
        double M = frame.cols / log(maxRadius);
        logPolar(frame, log_polar_img, center, M, flags);
        linearPolar(frame, lin_polar_img, center, maxRadius, flags);

        logPolar(log_polar_img, recovered_log_polar, center, M, flags + WARP_INVERSE_MAP);
        linearPolar(lin_polar_img, recovered_lin_polar_img, center, maxRadius, flags + WARP_INVERSE_MAP);
#endif

        // direct transform
        warpPolar(src, lin_polar_img, Size(),center, maxRadius, flags);                     // linear Polar
        warpPolar(src, log_polar_img, Size(),center, maxRadius, flags + WARP_POLAR_LOG);    // semilog Polar
        // inverse transform
        warpPolar(lin_polar_img, recovered_lin_polar_img, src.size(), center, maxRadius, flags + WARP_INVERSE_MAP);
        warpPolar(log_polar_img, recovered_log_polar, src.size(), center, maxRadius, flags + WARP_POLAR_LOG + WARP_INVERSE_MAP);

        // Below is the reverse transformation for (rho, phi)->(x, y) :
        Mat dst;
        if (flags & WARP_POLAR_LOG)
            dst = log_polar_img;
        else
            dst = lin_polar_img;
        //get a point from the polar image
        int rho = cvRound(dst.cols * 0.75);
        int phi = cvRound(dst.rows / 2.0);

        double angleRad, magnitude;
        double Kangle = dst.rows / CV_2PI;
        angleRad = phi / Kangle;
        if (flags & WARP_POLAR_LOG)
        {
            double Klog = dst.cols / std::log(maxRadius);
            magnitude = std::exp(rho / Klog);
        }
        else
        {
            double Klin = dst.cols / maxRadius;
            magnitude = rho / Klin;
        }
        int x = cvRound(center.x + magnitude * cos(angleRad));
        int y = cvRound(center.y + magnitude * sin(angleRad));
        drawMarker(src, Point(x, y), Scalar(0, 255, 0));
        drawMarker(dst, Point(rho, phi), Scalar(0, 255, 0));


#if 0  //C version
        CvMat src = frame;
        CvMat dst = lin_polar_img;
        CvMat inverse = recovered_lin_polar_img;
        cvLinearPolar(&src, &dst, center, maxRadius, flags);
        cvLinearPolar(&dst, &inverse, center, maxRadius,flags + WARP_INVERSE_MAP);
#endif

        imshow("Src frame", src);
        imshow("Log-Polar", log_polar_img);
        imshow("Linear-Polar", lin_polar_img);
        imshow("Recovered Linear-Polar", recovered_lin_polar_img );
        imshow("Recovered Log-Polar", recovered_log_polar );

        if( waitKey(10) >= 0 )
            break;
    }
    return 0;
}