title: Triangulating a 3D point using two camera images
body: <p>This seems rather simple but I can't find any answers online on how to get started.  I'm prepping for interviews and this was a question that my friend was asked.  Here it is:</p>
  <p><a href="https://i.stack.imgur.com/4zThX.png" rel="nofollow noreferrer">Coordinate System where z sticks out of the page</a></p>
  <ol>
  <li><p>I have two cameras in the world, with 3D coordinates p1 and p2.</p>
  </li>
  <li><p>The cameras have heading angles theta1 and theta 2, measured from the y axis</p>
  </li>
  <li><p>I know the focal length of the cameras f in pixels, and that the resolution is AxB pixels</p>
  </li>
  </ol>
  <p>4). The coordinates of the detections in the image plane, i.e., the pixel point on the image plane where the point we want to find shows up.</p>
  <p><a href="https://i.stack.imgur.com/fAkQO.jpg" rel="nofollow noreferrer">Here is a rough sketch of the scenario</a></p>
  <p>My thoughts so far are that I have to solve a system of equations but I believe a part of that is finding the camera matrix or the mapping from 3D to 2D space. Is it just making use of the focal length? I'm really lost here</p>