title: Converting 320x240x3 point cloud matrix to 320x240x1 depth map
body: <p>can anybody help me with the following problem using Python?</p>
  
  <p>I have point cloud matrix got from a virtual camera, its dimension is 320x240x3, which indicates x,y,z coordinates of each point (points in camera view).</p>
  
  <p>All values range from negative to positive. How can I convert this point cloud matrix to a 320x240x1 depth map which stores the positive depth value of each pixel? Thanks in advance.</p>