openCV usage cvFindDominantPoints - opencv

Question

Does anyone know how to use the cvFindDominantPoints API of openCV? I basically have a 1 channel, binary image from which I get a set of contours. Judging from the image, I seem to be getting the correct contours. Now, I am selecting one of these contours to get dominant points of. This contour has about 60 vertices. However, the API call to cvFindDominantPoints is giving me a sequence of points (about 15) that does not even lie on the contour. It is quite far from it. Any insight?
my usage:
CvSeq *dominantpoints = cvFindDominantPoints(targetSeq, tristorage, CV_DOMINANT_IPAN, 7, 9, 9, 150);

Answer 1

#include "cv.h"
#include "highgui.h"
CvSeq* contours = 0;
CvSeq* dps = 0;
int main( int argc, char** argv )
{
int i, idx;
CvPoint p;
CvMemStorage* storage_ct = cvCreateMemStorage(0);
CvMemStorage* storage_dp = cvCreateMemStorage(0);
IplImage* img = cvLoadImage("contour.bmp", CV_LOAD_IMAGE_GRAYSCALE);
cvNamedWindow( "image" );
cvShowImage( "image", img );
cvFindContours( img, storage_ct, &contours, sizeof(CvContour),
CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE );
dps = cvFindDominantPoints( contours, storage_dp, CV_DOMINANT_IPAN, 7, 20, 9, 150 );
contours = cvApproxPoly( contours, sizeof(CvContour), storage_ct, CV_POLY_APPROX_DP, 3, 1 );
printf("found %d DPs and %d Contours \n", dps->total, contours->total );
for ( i = 0; i < dps->total; i++)
{
idx = *(int *) cvGetSeqElem(dps, i);
p = *(CvPoint *) cvGetSeqElem(contours, idx);
cvDrawCircle( img, p , 1, cvScalarAll(255) );
printf("%d %d %d\n", idx, p.x, p.y);
}
cvDrawContours(img, contours, cvScalarAll(100), cvScalarAll(200), 100 );
cvNamedWindow( "contours" );
cvShowImage( "contours", img );
cvWaitKey(0);
cvReleaseMemStorage( &storage_ct );
cvReleaseMemStorage( &storage_dp );
cvReleaseImage( &img );
return 0;
}