hi,
I want to run lkdemo.c which comes as a sample of open cv.
Actually i am interested in using algorthim of optical flow in order
to track movement of an object for my project but it gives error which
says segmentation fault.my operating system is linux .it is showing video captured from camera correctly but as i start clicking the mouse on video in order to
track points on movement the video disappears and error appears.Kindly
help me out and see my code below;

#ifdef _CH_
#pragma package <opencv>
#endif

#ifndef _EiC
#include "cv.h"
#include "highgui.h"
#include <stdio.h>
#include <ctype.h>
#endif

IplImage *image = 0, *grey = 0, *prev_grey = 0, *pyramid = 0, *prev_pyramid = 0, *swap_temp;

int win_size = 10;
const int MAX_COUNT = 500;
CvPoint2D32f* points[2] = {0,0}, *swap_points;
char* status = 0;
int count = 0;
int need_to_init = 0;
int night_mode = 0;
int flags = 0;
int add_remove_pt = 0;
CvPoint pt;


void on_mouse( int event, int x, int y, int flags, void* param )
{
    if( !image )
        return;

    if( image->origin )
        y = image->height - y;

    if( event == CV_EVENT_LBUTTONDOWN )
    {
        pt = cvPoint(x,y);
        add_remove_pt = 1;
    }
}


int main( int argc, char** argv )
{
    CvCapture* capture = 0;
    
    if( argc == 1 || (argc == 2 && strlen(argv[1]) == 1 && isdigit(argv[1][0])))
        capture = cvCaptureFromCAM( argc == 2 ? argv[1][0] - '0' : 0 );
    else if( argc == 2 )
        capture = cvCaptureFromAVI( argv[1] );

    if( !capture )
    {
        fprintf(stderr,"Could not initialize capturing...\n");
        return -1;
    }

    /* print a welcome message, and the OpenCV version */
    printf ("Welcome to lkdemo, using OpenCV version %s (%d.%d.%d)\n",
	    CV_VERSION,
	    CV_MAJOR_VERSION, CV_MINOR_VERSION, CV_SUBMINOR_VERSION);

    printf( "Hot keys: \n"
            "\tESC - quit the program\n"
            "\tr - auto-initialize tracking\n"
            "\tc - delete all the points\n"
            "\tn - switch the \"night\" mode on/off\n"
            "To add/remove a feature point click it\n" );

    cvNamedWindow( "LkDemo", 0 );
    cvSetMouseCallback( "LkDemo", on_mouse, 0 );

    for(;;)
    {
        IplImage* frame = 0;
        int i, k, c;

        frame = cvQueryFrame( capture );
        if( !frame )
            break;

        if( !image )
        {
            /* allocate all the buffers */
            image = cvCreateImage( cvGetSize(frame), 8, 3 );
            image->origin = frame->origin;
            grey = cvCreateImage( cvGetSize(frame), 8, 1 );
            prev_grey = cvCreateImage( cvGetSize(frame), 8, 1 );
            pyramid = cvCreateImage( cvGetSize(frame), 8, 1 );
            prev_pyramid = cvCreateImage( cvGetSize(frame), 8, 1 );
            points[0] = (CvPoint2D32f*)cvAlloc(MAX_COUNT*sizeof(points[0][0]));
            points[1] = (CvPoint2D32f*)cvAlloc(MAX_COUNT*sizeof(points[0][0]));
            status = (char*)cvAlloc(MAX_COUNT);
            flags = 0;
        }

        cvCopy( frame, image, 0 );
        cvCvtColor( image, grey, CV_BGR2GRAY );

        if( night_mode )
            cvZero( image );
        
        if( need_to_init )
        {
            /* automatic initialization */
            IplImage* eig = cvCreateImage( cvGetSize(grey), 32, 1 );
            IplImage* temp = cvCreateImage( cvGetSize(grey), 32, 1 );
            double quality = 0.01;
            double min_distance = 10;

            count = MAX_COUNT;
            cvGoodFeaturesToTrack( grey, eig, temp, points[1], &count,
                                   quality, min_distance, 0, 3, 0, 0.04 );
            cvFindCornerSubPix( grey, points[1], count,
                cvSize(win_size,win_size), cvSize(-1,-1),
                cvTermCriteria(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS,20,0.03));
            cvReleaseImage( &eig );
            cvReleaseImage( &temp );

            add_remove_pt = 0;
        }
        else if( count > 0 )
        {
            cvCalcOpticalFlowPyrLK( prev_grey, grey, prev_pyramid, pyramid,
                points[0], points[1], count, cvSize(win_size,win_size), 3, status, 0,
                cvTermCriteria(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS,20,0.03), flags );
            flags |= CV_LKFLOW_PYR_A_READY;
            for( i = k = 0; i < count; i++ )
            {
                if( add_remove_pt )
                {
                    double dx = pt.x - points[1][i].x;
                    double dy = pt.y - points[1][i].y;

                    if( dx*dx + dy*dy <= 25 )
                    {
                        add_remove_pt = 0;
                        continue;
                    }
                }
                
                if( !status[i] )
                    continue;
                
                points[1][k++] = points[1][i];
                cvCircle( image, cvPointFrom32f(points[1][i]), 3, CV_RGB(0,255,0), -1, 8,0);
            }
            count = k;
        }

        if( add_remove_pt && count < MAX_COUNT )
        {
            points[1][count++] = cvPointTo32f(pt);
            cvFindCornerSubPix( grey, points[1] + count - 1, 1,
                cvSize(win_size,win_size), cvSize(-1,-1),
                cvTermCriteria(CV_TERMCRIT_ITER|CV_TERMCRIT_EPS,20,0.03));
            add_remove_pt = 0;
        }

        CV_SWAP( prev_grey, grey, swap_temp );
        CV_SWAP( prev_pyramid, pyramid, swap_temp );
        CV_SWAP( points[0], points[1], swap_points );
        need_to_init = 0;
        cvShowImage( "LkDemo", image );

        c = cvWaitKey(10);
        if( (char)c == 27 )
            break;
        switch( (char) c )
        {
        case 'r':
            need_to_init = 1;
            break;
        case 'c':
            count = 0;
            break;
        case 'n':
            night_mode ^= 1;
            break;
        default:
            ;
        }
    }

    cvReleaseCapture( &capture );
    cvDestroyWindow("LkDemo");

    return 0;
}

#ifdef _EiC
main(1,"lkdemo.c");
#endif

Waiting for your reply.
thanks.
Sana

Your best bet is to visit the maintainer site for that package, and
a) see if there are any updates
b) read the FAQ to see if it's a common problem with known answers
c) ask on THEIR forum, as there you will find the MOST people with the MOST experience of using it.

Joining random technical forums in the hope of getting lucky enough finding someone who knows about it isn't really the way forward.

Thanks for your reply.Well its run time error and it does not exactly show me where that error occur.Whenever i start it captures my video.According to the menu in the program whenever i press 'r' to auto initialize to track my body movement or click the video which is alternate method the video ends and it say segmentation error but it does not show me where exacty this error occur.

So compile it with gcc -g prog.c Then run the program as

gdb a.out
<<snip wordy gdb output>>
run

When it crashes, use 'bt' to print where it happened.
'up' and 'down' navigate the stack
'print' can print variables

Find out what variable contained a garbage value, and work from there.

So compile it with gcc -g prog.c Then run the program as

gdb a.out
<<snip wordy gdb output>>
run

When it crashes, use 'bt' to print where it happened.
'up' and 'down' navigate the stack
'print' can print variables

Find out what variable contained a garbage value, and work from there.

Or, run it in the debugger. When it crashes, the debugger will let you see what was going on (hopefully) to cause this. Post-mortem debugging using the core file is useful, but sometimes running in the debugger is more helpful.

Thanx.I tried the command which you told me but the only way lkdemo compiles is through building build_all.sh file which comes along with it.once we comiple this file lkdemo is ready to run otherwise it starts searching for header files it needs.Even i tried to give path of header where they were installed but it did not worked.Kindly,tll me some other solution.

So look through build_all.sh for where gcc is called.

Or perhaps where a variable (say CFLAGS) is set to a number of gcc options.

Either way, make sure the program is compiled with -g

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