P3D Re: Hypo - Ortho - Hyper OR convergence angle?

[Larry Berlin <lberlin@xxxxxxxxx>]

At 10:13 AM 12/5/97, Dr.T  wrote:
>.................  I think that if you want to go into details,
>the interocular distance and the FL of the lenses should be recorded.

*****  Yes, that would be true. 

>
>If you only give the convergence angle then only by knowing the size of
>your object you can understand the situation involved.  Many tricks in
>stereo photography are derived by playing games with the interocular
>distance and size of objects (or lack of clue of size).

****  Many times the size of an object is well known. In cases where it
isn't known or the artist intends to create an illusion of some sort, you
would deliberately withold some information until the image has been
enjoyed, and then reveal the real situation.

My point wasn't about most of the issues raised here, it was about the heavy
importance seemingly attached to the terms Hypo, Hyper and Ortho, especially
to beginners, as if these terms had some real meaning in the process of
obtaining good stereo pictures. The terms themselves are useful, to a
degree, but not to the degree that they are used in numerous other
discussions. This discussion has gotten off track relative to the intention
of my first remarks. I basically agree with most of what George is saying,
but I can still logically point out how the use of Hypo, and Hyper are
relatively meaningless in many situations. 

>.................
>Similarly, in the case of hyperstereos, it is possible that a person cannot
>tell the difference between a hyperstereo of a real scene or an ortho
>stereo of a real model (same convergence in both cases).  Knowing that this
>is a hyper gives the answer.

****  This might be a good example to look at closer. The point about
helping beginners understand stereo photography is about helping them create
an image of the model or an image of the building itself without having a
problem. The convergence angle, or the ratio of base to distance is far more
useful than saying truthfully that one image is a Hypo and the other is a
Hyper. Which is which? Just how hyper is the hyper or how hypo is the hypo?
How would a beginner understand the taking geometry from those terms alone?
They couldn't. Yet the taking geometry as described by either a ratio of
base to distance or the convergence angle, would enable the beginner to
duplicate the images pretty closely and feel confident in the process. 

You get information from hypo and hyper by making certain educated
assumptions. However, if someone else does the photography and the H words
are the *only* description provided to you, you wouldn't be able to
precisely reconstruct the original relationships either.

>............................
>
>What good would be to know the convergence angle if there is no clue about
>the size of the objects pictured?

*****  More useful than knowing such a picture, assuming something pretty
abstract is the subject, is a hypo. In the case of SEMs, it might be useful
to know what the object is, but knowing it's a Hypo is relatively
meaningless since ALL SEMs are hypos. I guess it's relative to what
information is important in each instance. Why do you want to know the size
of the actual object? Suppose that wasn't the intent of the photographer?
Suppose the intent was to show the model building as if it were the real
thing. They wouldn't want the audience to know relative size. But that's
beside the point, when the point is about helping beginners understand
taking geometry and be able to obtain good pictures of their own. A suitable
convergence angle or a ratio of base to distance is far more useful since
it's universal to any situation.

I never said the terms shouldn't be used. They are good terms and can be
very useful, but all too frequently they are over used. Used by themselves
they *can't* describe an actual taking geometry. I use the terms myself and
I'm aware that to have meaning there has to be other information present.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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