Morphometric
analysis is a tool used by palaeontologists, archaeologists,
anthropologists and forensic pathologists to analyse and compare
specimens. It relies on taking numerous measurements of an object
such as a bone or shell, and comparing both these measurements and
ratios between measurements to those obtained from other specimens in
order to establish relationships between them. Traditionally these
measurements have been obtained using tape measures and callipers,
but modern scientists often use more sophisticated tools such as
structured light scanners, which are capable of building highly
detailed three dimensional models of specimens. Photogrammmetry has
been used as a tool in landscape analysis since the mid nineteenth
century. It relies on taking overlapping images of a landscape, from
a number of different vantages, in order to help cartographers and
geomorphologists build up a three dimensional model of the landscape.
The advent of digital photography has led to a far wider use of
photogrammetry in the archaeology and other fields in the past two
decades, with it becoming regularly used to build models of
archaeological sites or even individual buildings. Recently some
scientists have begun using photogrammetry to build models of smaller
items, including archaeological artefacts and Human remains.
In a
paper published in the Journal of Archaeological Science: Reports on 18 July 2016 a team of scientists led by Allowen Evin of the Institutdes Sciences de l'Evolution at Université de Montpellier, the
Department of Archaeology at the University of Aberdeen, and the
Department of Archaeology, Classics and Egyptology at the Universityof Liverpool, describe a process by which three dimensional computer
models were constructed using digital photographs, and the results
compared to the results of a morphometric model made to by structured
light analysis.
Evin et
al. examined a series of five
modern Wolf skulls from the collection of the Muséum Nationald'Histoire Naturelle in Paris, as part of a study into morphometric
changes to the cranium during the domestication of Dogs. In order to
do this they created two models, one using a Breuckmann StereoScan
structured light scanner and the other a model constructed from a
series of photographs taken with a an 8 mega-pixel digital
single-lens reflex (DSLR) Canon EOS 30D camera, mounted with a CanonEF 24–105mmf/4 L IS USM lens.
In order to take the photographs the specimens were placed on a rigid
cardboard sheet with a calibrated referential pattern, and
photograped from three different elevations (approximately 0°, 15°
and 40°) using a tripod mounted camera, which was moved around the
specimen taking images at 10° intervals (i.e. 36 sets of three
images in a circle). This was then repeated with the skull the other
way up, to give a model of the complete specimen. These images were
then turned into a three dimensional model using a VisualSFM software
package.
(A)
Schematic representation of the set-up and camera positions used for
the acquisition of the photographs. (B) Fixed dimensions reference
pattern used to scale the models and enhance the performance of
key-points detection/matching and camera calibration algorithms. Evin
et al. (2016).
The photogrammatic model was then compared to the model made using
the Breuckmann StereoScan structured light scanner (which rotates the
specimens on its own automated turntable, creating a model using its
own Optocat software package) using a computed mesh-to-mesh deviation
map to compare the topology of the two models. This found that the
two models matched to an average of 0.088 mm, with the only
significant differences occurring within the nasal cavity and
occipital foramen, areas which are generally considered extremely
difficult to measure accurately, and which are not usually included
in morphometric analyses.
Models obtained with photogrammetry (top) and the Breuckmann
structured light scanner (bottom) with the cloud-mesh distances
visualisation (middle). Differences are expressed using the colour
scale on the left. Evin et al. (2016).
Evin et al. note the total tine spent with each specimen while
capturing the images used to create the photogrammetric model was
about 15 minutes, while the Breuckmann scanner required about forty
five minutes to scan each specimen, although having scanned the
specimens the Breuckmann scanner was able to produce a model almost
instantaneously, while the camera method required considerable
further input from the users, so that the Breuckmann scanner method
took less time overall.
However since the Breuckmann scanner is not portable and is reliant
on specimens being brought to it, Evin et al. felt that on the
whole the advantages of the camera outweighed those of the scanner,
as it could potentially be used in situations where specimens could
not be moved, was considerably cheaper and captured additional
information about the colour and surface texture of the specimen that
were not recovered with the scanner.
See also...
X-ray Computed Tomography studies of two Woolly Mammoth calves from Russia. The Woolly Mammoth, Mammuthus
primigenius, is thought to have diverged from the earlier Steppe Mammoth Mammuthus trogontherii in northeast...
Using morphometric analysis to understand the nature of Canid remains from Plio-Pleistocene Hominid sites from East Africa. Morphometric analysis is a method used...
Reconstructing the Paluxy River Dinosaur Chase Sequence. In 1940 palaeontologist Roland Bird of the American Museum of Natural History in New York described and partially excavated a sequence of Dinosaur
footprints along the Paluxy River at Glen Rose in...
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