Check if homography is good

edit

Basically I a am using a function

bool niceHomography(const CvMat * H)
{
  const double det = cvmGet(H, 0, 0) * cvmGet(H, 1, 1) - cvmGet(H, 1, 0) * cvmGet(H, 0, 1);
  if (det < 0)
    return false;

  const double N1 = sqrt(cvmGet(H, 0, 0) * cvmGet(H, 0, 0) + cvmGet(H, 1, 0) * cvmGet(H, 1, 0));
  if (N1 > 4 || N1 < 0.1)
    return false;

  const double N2 = sqrt(cvmGet(H, 0, 1) * cvmGet(H, 0, 1) + cvmGet(H, 1, 1) * cvmGet(H, 1, 1));
  if (N2 > 4 || N2 < 0.1)
    return false;

  const double N3 = sqrt(cvmGet(H, 2, 0) * cvmGet(H, 2, 0) + cvmGet(H, 2, 1) * cvmGet(H, 2, 1));
  if (N3 > 0.002)
    return false;

  return true;
}

to check whatever the homography is good or not (I have taken it from BRIEF_demo). Can anyone explain why we check the determinant like that, is there any theory behind it?

To understand what I am talking about, that function avoids homography like this:

Thanks