float fVmag = sqrt((float)((points[0][i].x-points[1][i].x)*(points[0][i].x-points[1][i].x)+(points[0][i].y-points[1][i].y)*(points[0][i].y-points[0][i].y)));
now I want to access only the vector length that are presented on the left side of the image. I was thinking to use image.cols/2 to split it into two equal parts. But I dont know how to access the data inside that region.