Re: Aerial hyperstereos

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Clifford J. Mugnier writes

>>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.

>Cliff Responds:
>Best spacing for hyper out of a plane's window?  Take one, watch the 
>>overlap overage 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 ...

Your comments on aerial photography mapping are correct for taking vertical
aerial photos, but the constants when taking vertical shots are fixed thus
the stereo base is constant. In oblique aerial 3d photography that was
being discussed the focal lengths were variable. If the pictures are taken
at 40% displacement as you suggest what will happen is that at higher focal
lengths the stereo base will be quite short and thus very little 3d effect.
At shorter focal lengths the opposite effect will result and a much wider
stereo base with corresponding hyper stereo. Thus the stereo base will be
effected by the focal length if a constant 40% horizontal displacement is
kept when taking consecutive shots. This is not due to the focal length but
rather to keeping the horizontal displacement constant at 40% with
different F.L.. Now if instead of taking the shots at 40% displacement, one
takes the pics after the plane has travelled a fixed distance of one mile
for example the result would be- Stereo pairs taken at hi F.L. or short F.L.
will have the same stereobase. There is a subtle reason for this and if you
read my original post you will find the explanation.
Thanks for making a simple concept complicated. ;;;-)

Gabriel

P.S. Picked up a very fine aerial 3d map viewer last week. 
Sturdy metal construction with front surface mirrors and
comes with binocular magnifiers. Wooden case and looks like
it was made in the 50's. Made in England. Much better than
my Australian green plastic version. :-)

P.S.S See my house in glorious anaglpyh mode. Sorry Dr.T you'll need to get
something better than those 25 cents cardboard types to view it. ;-)
http://generation.net/~jacob/myhouse.jpg


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