title: Determining if a 3D point is in front of a pair of stereo camera, given their essential matrix
body: <p>I'm trying to obtain the 3D metric reconstruction of the points I have in two different views of my scene by means of a pair of iPhone 4S (a rudimental stereo system).</p>
  
  <p>To do so, I did calibrate the cameras, estimate the fundamental matrix and obtained an estimate of the essential matrix. Now, in Hartley&amp;Zisserman "Multiple View Geometry in CV" book, I see that to any given E, they correspond 4 canonical cameras pairs, of which only one reconstructs as the "actual" stereo configuration.</p>
  
  <p>The problem is that they say [cit.]"...the reconstructed point will be in front of both cameras in one of these four solutions only. Thus, testing with a single point to determine if it is in front of both cameras is sufficient to decide between the four different solutions for the camera matrix P'. ..."</p>
  
  <p>Given that I know F, K_left and K_right, how does one establish whether a 3D point is in front of both cameras or not?</p>
  
  <p>Thanks,</p>
  
  <p>Riccardo</p>