Re: Stereo to photogrammetry

[P3D <CJMCE@xxxxxxxxxxxxxxxx>]

Colin Moyer said:

>        My reason for asking is that I am an archaeologist and am
>interested in creating a visual and metrical database of Neanderthal stone
>tools while I am excavating at a site in France this summer.  I will likely
>be using an SLR with a sliding rail for the close-ups of the artefacts,
>this will give me good control over the stereo-base (which is necessary for
>photogrammetry), 

Not true.

>and it will give me a good sized (full-frame)
>negative/slide.  The principal is essentially the same as going from aerial
>photography --> elevation maps, which is done all the time.  But I will not
>be using fancy aerial cameras (which have build in index marks for
>measurement, and corrected lenses), nor can I afford "terrestrial
>photogrammetric" systems.

"index marks" are called fiducials.

"Terrestrial Photogrammetric Systems" nowadays consists of a Nikon 35mm camera
with a Nikon "Micro-Nikkor" 55mm or 60mm lens.

>Questions:

>Is there an easy way to put index marks on your negative/slide without
>wrecking my camera?  Do ready made attachments for such things exist?

There's easier ways to do this with software (mainly my software).
Ready-made attachments exist, but (pardon my Copyright infringement; they
are Micky-Mouse).
                  (Inside joke for Photo-3D).

>Will a standard 50mm or other standard lense cause distortion, making
>measurement impossible? or can such distortion, if it exists, be corrected
>for?

If the distortion is KNOWN, it can be corrected for... That's the nature of
systematic error - if you know what the "system" is, then change the sign of
the coefficients and you can then correct (cancel out) the distortion.  That,
however, implies that you calibrate your lens for radial lens distortion.
My software does that with remarkably simple tools if you have a scanner or
a digital camera.  Without either, you need a photogrammetric instrument called
a "comparator" to measure the negative.  "Standard" 50mm lenses do have
measurable distortion, but if you use a special low-distortion lens made for
copying - you can usually ignore a lens calibration for many low-precision
purposes (such as yours).  In the photographic trade, that kind of lens is
known as a "Macro" or "Micro" lens.  They usually cost less than $500.00, and
for photogrammetric applications they are well worth the expense.  Second-hand
versions are perfectly acceptable if they have not been dropped.  (Look for
dents in the lens barrel.)

>Is there relatively cheap software to make digital elevation models from
>stereo-pairs? (The only one I have seen cost over 10,000 dollars and
>required a Silicon Graphics workstation, which I have no real access to at
>the moment).

Yep, my stuff is $1,995.00 and I offer a 20% discount if the Purchase Order is
from a University.  It works on a PC; needs at least 640K memory.

>In general, does anyone on the list do photogrammetry?

You betcha.

>Does anyone do archaeology?

Most everybody with a stereo camera.

Furthermore;

George Themelis said:

>It is not clear to me why you will be recording these pictures.  At first,
>it sounds as if you are doing stereo photography for documentation.  The
>use of the word "photogrammetry" implies that you want to do measurements
>on the pictures to recreate true sizes of objects.  Since you are looking
>and can handle the ojects (unlike aerial or SEM photogrammetry) why don't
>you measure them directly with a ruler???

I agree; why don't you use a ruler?

If you want more information on software, etc.; e-mail me directly & I'll
send you a free working demo to play with.  Current academic research with
my software includes:

Bio-photogrammetric work on Human Cadaver Heads under impact crashes 
(High Speed photography @ 500-1000 frames/second)
                                               2 Universities in Wisconsin

Wave-pattern analysis of shallow water/slope interaction

                                                 Oregon Graduate School

Industrial Photogrammetry
                                                 University of New Orleans &
                                                 Ryerson Universiy, Montreal

Aerial Photogrammetry                            King Saud University,
                                                 Riyadh, Saudi Arabia

                                                 Royal Melbourne Institute
                                                 of Technology, Australia

                                                 et cetera ...

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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