Aligning Aerials

[RJ Thorpe <thorpe@xxxxxxxx>]

KWKelly wrote:

> I have some aerial images which are what I call "unintentional or
serendipity 3D."

KW,

I used to take handheld aerial 3D shots all the time when I was the
City of Cedar Rapids' photograper. There are two basic things to watch
out for. The first is the alignment factor that you mention. The second
is extreme parallax because there is too much distance between the two 
shots.

Alignment differences
You can correct this quite easily. Take a look on my page about how to
fix it. The page was intended for stereocards, but MF transparencies 
are so darn close to the same size that all the principles still apply.
The URL is:

     http://www.skep.com/3D/line-up.htm

Be sure to click the Holmes Stereo Mounting page link at the bottom
because it has some other useful information that you can get by 
reading between the lines.

Extreme Parallax
This topic is not on my web page but I have experienced exactly what
you are talking about and can offer a few suggestions. When you are
flying along, it is very easy to let too much ground go by you between
pictures. This makes the forground image irreconcilable. Sometimes the
mountain in the background is still there but the foreground is 
completely different. For the most part these cannot be used. There is
too much to do to fix them. If the same features are in both shots,
but the angle between them is great, you can overlap the nearest
objects (once they are aligned and trimmed) and trim off the outside
edges [See Holmes Stereocard page]. This usually results in a much
narrower final image but it makes it much easier on the eyes to view
it. It will be extremely hyper. Another alternative is to trim off the
bottoms of the shots till you have the same features in both slides,
then overlap and trim the sides. With MF slide mounts, you will 
probably have to use the 645 aperture models. Talk to Joel about that.

-- 
RJ Thorpe
Cedar Rapids, IA
mailto:thorpe@xxxxxxxx
http://www.skep.com