[tech-3d] Subject: Re: Stereo Base Calculation With a $20.00 Handheld

["Michael K. Davis" <zilch0@xxxxxxxxxxxx>]

Andres,

I've been away for a week...

>Date: Thu, 23 Nov 2000 08:04:25 -0500
>From: Andres Posada O <aposadao@xxxxxxxxxx>
>Subject: Re: Re: Stereo Base Calculation with a $20.00 Handheld
>
[snip]
>
>Michael:
>   In my HP48G+ I can solve for what ever I want (anybody with the
>formulas in a computer or the like may obviopusly do it). Doing 3D video
>I am usually stuck to minimum camera separations, dictated by the camera
>sizes, that require that I solve for near point, sometimes I need to
>solve for far point. 

I acknowledge the usefulness of solving for parameters other than base and
appreciate your comment for its testimony of the usefulness of the General
Solution.  

The abilities of the HP 48G+ aside, I've never seen the General Solution
expressed as a solution for d (deviation), in print or online.  The point I
was making in the article to which you are responding was that no newbie is
likely to find himself in the quandary described by Abram:

>>Date: Mon, 20 Nov 2000 15:52:01 -0000
>>From: "Abram Klooswyk"
[snip]
>>Michael Davis wonders why I call the so-called "General Solution" 
>>paradoxical.
>>The formula is for base calculation, to get a base which results in 
>>a viewable deviation. Many newbies like such a rule. However, the 
>>formula next asks for an _input_ of the deviation which it should 
>>provide as _outcome_ on film, after _using_ the calculated base. 
>>Newbies will ask: what deviation?
>>You can calculate it from the base, and than get in an endless 
>>regression. In discussions many different values for deviation are 
>>mentioned, which isn't particular helpful for newbies.

Again, given that 99% (?) of documentation on the General Solution solves
for base, the point of my article was: 

>>   Date: Wed, 22 Nov 2000 23:31:39 -0600
>>   From: "Michael K. Davis" <zilch0@xxxxxxxxxxxx>
>>
[snip]
>>I can't imagine any newbies actually doing the math to rearrange the
>>General Solution in the first place, much less finding themselves in an
>>endless regression, solving for deviation, then for base, then for
>>deviation, then for base, etc.  

Lastly,

Although you wrote that you almost never solve for base, I noticed that the
examples you gave had you solving for parameters other than deviation:

>For example: if I have a minumum camera separation
>due to camera size of say 165mm, and the nearest object is going to be
>at 3000mm, then how far may the farthest object be, all this subjected
>to a MOFD choosen according to CCD size, lens focal length and TASTE.
>What happens to the near point if I change the focal length position in
>the cameras zoom lenses? Everything changes if I use 1/3", 1/2", or 3/4"
>CCDs cameras. MOFD numbers I change according obviously to CCD size, but
>also I use more "liberal" numbers if all subjects are inside the window,
>be more conservative with subjects way out of the window and near to the
>camera. My point is I almost never solve for base.

In these examples, you are choosing a value for deviation, not solving for
it.  I'm willing to concede that someone out there has a use for an
equation that solves for deviation, but contrary to Abram's contention, I
suspect the greenest of newcomers would understand that an equation that
solves for base uses variables that are supplied by the user, not
calculated by rearranging the equation!  

Mike


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