title: gluPerspective parameters- what do they mean?
body: <p>I wonder about the <code>gluPerspective</code> parameters.</p>
  
  <p>In all examples I see <code>fovy</code> is set to around 45-60degrees
  I've tried to set it to different values and the object just disappears 
  what's the explanation for it? </p>
  
  <p>The <code>aspect</code> value should always be the ratio? why would one change it?</p>
  
  <p><code>zNear, zFar</code> - once again the usual values are around 10 and 500+ what does it reflect?</p>