Re: Aerial hyperstereos

[P3D <CJMCE@xxxxxxxxxxxxxxxx>]

Gabriel said:

>You have a point that on the lower altitude shots they should be taken
>quicker but the focal length shouldn't be a concern regarding the stereo
>base. The focal length won't change the perspective of the view. Only the
>actual distance from the camera to the object accomplishes this.

Standard aerial photography is flown for a nominal 60% forward overlap.  That is
so that a continuous flight line will yield continuous stereo coverage without
any holidays (monoscopic coverage).  When the aerial photographer prepares to
set the intervalometer (timer) for the beginning of a flight line, he first 
waits for acknowledgement from the pilot that he is "on line".  With that done,
the photographer looks through a viewfinder and waits for the first photo point
to become visible in the viewfinder.  When that is viewed, he starts the timer.
The photographer then continues to monitor the viewfinder so that he can tell
when that point has traversed 40% of the way off of the viewfinder.  When that
instant occurs, he punches the intervalometer again, and the timer is now set 
for the approximate interval based on apparent ground speed.  That is monitored
from photo-to-photo to insure that cross-winds, etc. do not require any further
correction.

Best spacing for hyper out of a plane's window?  Take one, watch the overlap
coverage and punch another after 40%, and so on and so forth.  If you don't
want to take a whole series of continuous photos; only two, then after that
40% passes (which is based on the plane's speed and the focal length of the 
lens) - rotate the aim of the camera to get 100% coverage (slight keystone).

If I explained the above adequately, this should allow the K.I.S.S. principle
to prevail ...

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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