P3D Re: Projection and mounting, terminology

[Bruce Springsteen <bsspringsteen@xxxxxxxxx>]

Abram Klooswyk wrote:

> In my opinion studying a stereoglossary before studying the 
> technical papers would be better :-) The only problem is that 
> no real authoritative glossary exists :-(.

Ah, we need a real authority to create a real authoritative glossary.  The
first term we must define is "authority". :-)  Of course, an authoritative
stereoglossary cannot exist if it does not emerge from and make reference
to an authoritative stereophilosophy! :-(

> 1. Separation 
> I would recommend the term "separation" to indicate _all_ left 
> to right distances of "items" in stereoscopy. This includes 
> lens separation of stereocameras, camera separation in 
> hyperstereo, separation of homologues on stereoslides and 
> printed stereoviews, (also infinity-, far- and nearpoint 
> separation), separation of image apertures in stereocameras, 
> and of mask apertures of 41 x 101 masks, separation of viewer 
> lenses and eventually projection lenses.

This is very good, and follows Ferwerda, and I vote "yes".  Another way to
say it is:  Separation refers to distance between a "left" item and its
corresponding "right" item.

> It is a good thing to have different terms for X-direction 
> distances ("separation") and Z-direction distances ("distance" 
> in a narrower sense).

Is there any need to reserve a term for Y-direction measurements? 
"Elevation"?  Maybe not.

> A lot of confusion is avoided by being able to use these 
> different terms for different concepts.

Indeed!  And the corollary of this is that much confusion is caused by
using a single term for many different things.  Or many terms for the same
thing.

> 2. Deviation
> By strict definition this should be the difference between
> on slide infinity separation and any smaller on slide 
> separation. In this way we get near point deviation and window
deviation, 
> the latter being the difference between infinity separation 
> and mask aperture separation.

Perhaps "absolute deviation" for deviation from infinity?.  Is this a
linear measurement, or an angular one?

> Less strictly applied deviation 
> could also mean the difference between far point separation 
> and any smaller on slide separation, as in many scenes no 
> infinity is included.

Perhaps "local deviation"?  So "deviation" is the difference between any
horizontal measurement *within* a left item, and the corresponding
measurement in a right item.  Expressible as an angular or a linear value.

> 3. Convergence 
> In stereoscopy the term convergence applies to lines or 
> directions, like lines of sight or optical axes. These lines 
> or directions converge if they meet at a common point closer 
> than infinity. 

Always expressed aas an angle.  Zero convergence is when the eyes fixate
on an object at infinity in reality.  Positive values of convergence are
for fixating on a nearer object.  Divergence would have a *negative*
convergence value? 
 
Is there a good term for the direction of the deviation in a single stereo
image in a pair?  This must be found before mounting a print, for
instance. I'm trying to think of a simple term for this.

Bruce
__________________________________________________
Do You Yahoo!?
Talk to your friends online with Yahoo! Messenger.
http://im.yahoo.com