From: decwrl!fernwood!well.sf.ca.us!well!nagle@uunet.UU.NET (John Nagle)
Subject: Re: frame rates (was: We need a new language)
Date: 6 Feb 91 08:28:15 GMT



     Much confusion here.

     Existing VR systems of the head-mounted display class (VPL, Autodesk)
tend to have serious problems with a lag between head movement and display
update.  Most of this lag is not due to the rendering system, even though
the rendering updates are well below the 30Hz rate of ordinary TV, but
due to the very slow and noisy Polyhemus position sensor.  Not only is
this device only good for a few data points per second, due to noise
problems, it is necessary to pass the data through a low-pass filter
before using it.  This has the annoying result that when you turn your
head, the rendered image takes a substantial fraction of a second
to catch up.  Not only that, when it finally does catch up, it
settles slowly, rather than matching your head's deceleration rate.
This makes fast head motion at least counterproductive, and at
worst may interfere with one's sense of balance.  Whether it will
cause nausea is unclear.  But it definitely discourages rapid
head rotation.  

     Some people think this is a psychedelic experience.  Some
of these people took too many drugs in the 1960s.


                                        John Nagle