need atleast 4 corresponding points to calculate homography

modules/calib3d/src/fundam.cpp

@@ -374,6 +374,9 @@ cv::Mat cv::findHomography( InputArray _points1, InputArray _points2,
                 return Mat();
             convertPointsFromHomogeneous(p, p);
         }
+        // Need at least 4 point correspondences to calculate Homography
+        if( npoints < 4 )
+            CV_Error(Error::StsVecLengthErr , "The input arrays should have at least 4 corresponding point sets to calculate Homography");
         p.reshape(2, npoints).convertTo(m, CV_32F);
     }