Biology Reference
In-Depth Information
2.3.4 Landmarks from images
The collection of two-dimensional landmarks from projections of forms
onto film or paper has a long and rich history in biological research.
Camera Lucida drawings of objects viewed under a microscope, clinical
x-rays taken using a roentgenographic cephalometer, and simple pho-
tographs taken with attention paid to scale can all be used as a source
from which to collect landmarks. All that is required is that a grid of
known scale be superimposed over the stationary image, and points
located on the biological form and their coordinates be noted for later
analysis. Although collection of these coordinates can be done with
pencil and paper, two-dimensional digitizing tablets that attach to a
computer increase the speed and precision of data collection. These
digitizing tablets are inexpensive and ubiquitous (see Digitizers,
above).
Stereophotogrammetry has been used to collect three-dimensional
coordinate data in biological analysis (e.g., Creel, 1978; Hartman,
1986). This method requires a specialized camera system. Two expo-
sures, a stereo pair, are made of a single object. The pair represents the
object from two slightly different perspectives. A specialized stereo-
plotter, of the sort used in cartography to construct contour maps from
aerial photos, is then used to project a dot onto a landmark location.
The position of the dot in X, Y, and Z space is measured by the
stereophotogrammetric system. The usual stereophotogrammetric sys-
tems (including cameras and plotters) are expensive. Simplified short
base stereophotogrammetry instruments were developed for clinical
applications in the 1960s (Beard, 1967; Burke and Beard, 1967) and
have been used to measure change in facial morphology due to growth.
Biostereometrics is an expansive field with a rich history and a vast
literature, which we will not attempt to document here.
Diagnostic medical imaging in the form of computed tomography
(CT) and magnetic resonance imaging (MRI) has become routine in
medical practice and fairly common in biological research. The avail-
ability of large data sets at little or no cost and public domain imaging
software for viewing images makes this type of data a practical
research alternative for most laboratories. For example, anatomical
data are available via the Internet from the Visible Human Project
index.en.html
) and the Visible Embryo project. Software tools that are
available free of charge via the Internet include
NIH image,
available
via the Research Services branch of the National Institute of Mental
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