title: OpenGL: Why look down along -z axis in eye space?
body: <p>I learned that, when we use perspective projection, we look down along -z axis in eye space, which means we set the points with negative z values in eye space at first, and then divide them by -z in perspective division converting the z values back to positive values.</p>
  
  <p>But why bother? If we just draw the points in the first quadrant initially, there will be no such positive and negative conversions at all. If this is just a convention, why we use positive z values when we use orthographic projection? Now I'm reading a STL file, which saves the points in positives coordinates, should I still convert them into negative values and convert them back in prospective division? </p>