🚀 go-pugleaf

dchapman@ncsa.uiuc.edu (Dee A. Chapman) writes:

>I've noticed some "distortion" in viewing 3D graphics objects which
>were rendered using an SGI SkyWriter (GL Library).  For example, if I 
>create two divergent rectangular boxes, and view them on the flat screen
>of the computer console, they will appear to converge or be parallel:
>
>I believe this effect is due to the use of the "perspective" GL
>library call.  (void perspective(Angle fovy,aspect, znear, zfar)) I
>realize that the objects should appear to converge as they get farther
>away from the viewer, however the effect I'm referring to is that
>them seem to converge excessively. I can lessen this "converging" effect 
>>by varying the fovy parameter.  However, this can introduce other 
>inaccuracies. 

The effect is caused by an excesive FOV for your viewing situation.
The FOV csnnot be too wide: the angle should be 2*atan(w/2/d), where d
is the distance from your eye to the monitor, and w is the width of
the monitor screen (or window).  You can often go up to twice this FOV
without adding excessive distortion.  Still, it's restrictive.

>>From a simulation point of view, I'd like to make this graphics 
>representation 
>as close to "real" life representation as possible.


>
>In addition, I've noticed when I view the 3D graphics objects using
>a Flight Helmet head mounted display, the "converging" effect is
>lessened.  I'm thinking that is probably due to the lensing in the

No, this is because the FOV of the HMD matches the FOV parameter in
your software better.  I see this all the time with wide-angle
displays for REND386--it's not a bug, it's a feature! (B-{))


--------------------------------------------------------------------------
| My life is Hardware,                    |         Dave Stampe          | 
| my destiny is Software,                 | dstampe@psych.toronto.edu    |
| my CPU is Wetware...                    | dstampe@sunee.uwaterloo.ca   | 
| Am I a techno-psychologist, or just an engineer dabbling in psychology?|
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In article <1jvlreINNcu5@shelley.u.washington.edu>,
dchapman@ncsa.uiuc.edu (Dee A. Chapman) writes:

|> I've noticed some "distortion" in viewing 3D graphics objects which
|> were rendered using an SGI SkyWriter (GL Library).  For example, if I 
|> create two divergent rectangular boxes, and view them on the flat screen
|> of the computer console, they will appear to converge or be parallel:
|> etc

I have an article dealing with this and if I remember it correctly it
has to do with the viewer's inter pupillary distance. Ill have to
reread it to be sure though.  The article does, however, give some
explaination for it.

        "A Computational Model for the Stereoscopic 
                Optics of a Head Mounted Display"

                Warren Robinett
                Jannick P. Rolland
                UNC - CS dept

                SPIE vol 1457
                Stereoscopic Displays and Applications II (1991)