すべて..問題を解決しました...最初に、一致した適切なキーポイントをCvpointsに変換し、Cvpointsから座標を取得しました..同じコードは以下のとおりです-
for( i =0; i <good_matches.size(); i++ )
{
// the keypoints from the good matches only
points1.push_back( keypoints1[ good_matches[i].queryIdx ].pt );
points2.push_back( keypoints2[ good_matches[i].trainIdx ].pt );
printf("xco-ordinate of good mathched keypoints in image1 %d\n\n",points1[i].x);
printf("y co-ordinate for image 1 %d \n\n",points1[i].y);
printf("x co-ordinate for image2 %d \n\n",points2[i].x);
printf("y co-ordinate for image2 %d\n\n",points2[i].y);
}