Re: Aerial hyperstereos

[P3D <CJMCE@xxxxxxxxxxxxxxxx>]

George Themelis wrote:

>1. What is the justification of the 60 overlap?  Does it come for
>experience for good topographical relief or is it related to the way the
>pairs are viewed & analyzed?  Is it independent of the distance from the
>ground?

It's independent of the distance from the ground.  60% gives continuous stereo
with a 9.999% safety factor.  Variations in the overlap within that 10% can 
allow for slight adjustments in the "base-height ratio".  This is intended for
vertical aerial photography, but works also for obliques (out the window).

>2. Given that 60 overlap will force the slide film user to mount full frame
>slides in 5p or even 4p mounts, do you recommend convergence?  How slight
>is the resulting keystoning? 

I usually shoot print film for this, and I have found convergence to work
adequately for viewing with a stereoscope or freeviewing.  The keystoning is
negligible in my experience (for prints).  However, I prefer to shoot what is
called "low obliques" which do NOT include the horizon ("high obliques").
Perhaps that is the subtle difference that Gabriel refers to.  Anyway, it
works for me.  I still think it's simple this way.


Clifford J. Mugnier  (cjmce@xxxxxxx)
Topographic Engineering Laboratory
Department of Civil & Environmental Engineering
University of New Orleans
New Orleans, Louisiana  70148
Voice: (504) 280-7095
FAX:         280-7095


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