title: calculating objects height from video by knowing the homography in OpenCV
body: <p>I'm trying to measure the heights of the objects detected in my tracking application I'm developing using OpenCV and Python. I've calculated the homography matrix so I know every object's location in the real world and it's apparent height on the video frame. What I don't know is the real world position of the camera. I've seen that the camera pose matrix can be calculated from the homography, but I'm not sure what to do with that.</p>
  
  <p>The video is recorded from head level and the objects are mostly people. The homography transforms the camera pixels to the ground level.</p>
  
  <p>The width of the objects can be measured by transforming the leftmost and rightmost coordinates to real world coordinates and measuring the distance between them. How can I calculate the height?</p>