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Paolo De Leva
07-31-2008, 04:55 AM
Dear subscribers,

as you know, "stereophotogrammetric system" (SPM system) has a generic
meaning (see etymology below). SPM systems include systems which measure
static objects:
- Based on film photography
- Based on digital photography
- Roentgen SPM systems (3-D radiography or fluoroscopy)
(radiographies or fluoroscopic images are a special kind of "photograms")
And also systems which measure "motion" (a time sequence of positions):
- Cinematographic systems
- Analog-video-based optical SPM systems
- Digital-video-based optical SPM systems
- (3-D video-fluoroscopy? I am not sure if this is used to analyze motion)

These systems are quite different from each other, as far as their accuracy,
applications, drawbacks and advantages are concerned. Indeed, we often use
the expression "optoelectronic SPM system", to distinguish systems based on
analog video, digital video or digital photography from those which are not
optical (radiographic or fluoroscopic systems) or not electronic (systems
which require image recording on photographic film).

But sometimes we need a greater specificity. For instance, one of the most
specific expressions I have ever read was used by Chiari et al. (2005). They
wrote "video-based optoelectronic stereophotogrammetric system". I shortly
discussed this terminology with one of the authors (A. Leardini), and he
explained their rationale: "optoelectronic" was necessary to exclude the
above mentioned non-optoelectronic systems, but it was not enough to
uniquely identify systems for motion analysis: digital photographic cameras
are optoelectronic. These distinctions were relevant in the context of their
article, which was about instrumental errors. Thus, both the words "video"
and "opto" (or "optical") were necessary. However, the expression is
redundant because "video-based" implies "electronic", and implies the use of
a sequence of "photograms" (see etymology below).

In sum, in biomechanics there is a need for expressions to indicate
particular kinds of SPM systems, for instance those which can be used for
human motion analysys (HMA), and are based on electronic technology (as
opposed to cinematographic technology). Since the term "video" refers to
electronic motion recording (see etymology below), let's call these systems
"stereovideometric systems" (SVM systems). In sum:

- "SPM system" is too generic to uniquely identify a system for HMA
(it includes
- "Optoelectronic SPM system" is more specific, but not enough to specify a
system for HMA.
- "SVM system" is specific enough.
- "Video-based optoelectronic SPM system" is even more specific, but
redundant.
- "Video-based optical SPM system" is equivalent to the previous expression,
but shorter.
- "Optical SVM system" is equivalent to the previous expression, but even
shorter.

The term "videometry" and the expression "digital videometry" are frequently
used in the scientific literature; a search with http://www.google.com
confirms this). Notice that "video" implies "electronic", but neither
implies "optical" nor "digital" (video-fluoroscopes are not optical, and
analog video cameras are not digital). If you need to be more specific, you
can use "digital optical SVM system", and you can add other specifications
such as "passive-marker", "active-marker", or "markerless".

CONCLUSION
I conclude that the term "stereophotogrammetric" (SPM) is too generic in
many circumstances, and "stereovideometric" (SVM) is useful whenever SPM is
too generic. Thus, I propose to include this term in our vocabulary.

ETIMOLOGY
Stereophotogrammetric =
[stereo, from Greek stereos = solid] +
[photogram = 2-D image recorded by capturing light photons or X-ray
photons,
from Greek fos (genitive: fotÚs) = light and grafŤin = to
write] +
[metric = related to a measure or used to measure, form Greek metron =
measure].

Stereovideometric =
[stereo, from Greek stereos = solid] +
[video = electronic (not necessarily optoelectronic) technology, to
record
motion with a sequence of 2-D images, from Latin video = I see]
+
[metric = related to a measure or used to measure, form Greek metron =
measure].

Optical = related to vision or to optics, the science that describes the
behavior and properties of light and its interaction with matter (from Greek
optikÚs = related to vision, in turn from Úps = eye).

REFERENCE
Chiari L, Della Croce U, Leardini A, Cappozzo A. (2005). Human movement
analysis using stereophotogrammetry. Part 2: instrumental errors. Gait &
Posture 21(2):197-211. (Review)

With kind regards,

Paolo de Leva
Laboratory of Locomotor Apparatus Bioengineering
Department of Human Movement and Sport Sciences
University of Rome - Foro Italico
Italy