Morphometric Data - An Invariant Approach to Statistical Analysis of Shapes - page 31

cation. Reflex Measurement Ltd. has developed an auto-focusing facility
device that automates measurement along the Z-axis. We have not yet
published our repeatability studies using this device.

Surface scanners

Surface scanners are devices that make use of a variety of digital 3D
sensing techniques to produce a high resolution image of the surface of
objects. The surface is recorded as a series of closely spaced points in
3D space. For example, Coward and McConathy's (1995) facial images
each consist of 256,000 points. Landmarks can be identified on imaged
surfaces, and coordinate data can be collected from those surfaces. A
large number of surface scanners are available for use in the study of
biological morphology. If a laser scanner is readily available, this is a
reliable way to collect landmark data (Kohn and Cheverud, 1992).
Moreover, if specimens are of a difficult size, scanning an entire speci-
men enables one to either scale the specimen up (as in the case of
Eocene primates) or down (as in the case of Neoceratopsian dinosaurs)
for digitization. This enables data collection from an organism that
would be difficult or impossible to digitize in its natural state.

2.3.2 Digitizing whole specimens in multiple phases

When collecting coordinate data from whole specimens, it is essential
that the specimen remain stable. If the specimen is jostled or moved
during the digitization process, the integrity of the relative location of
landmarks is lost and the digitization procedure needs to be restarted.
To ensure stability, it is necessary to secure the specimen in place.
Pressing a specimen into a mound of clay is a common practice. When
this is done, a portion of the specimen is hidden from view while the
remainder is being digitized. After digitizing one side of the specimen,
it must be repositioned in order to collect landmark data from the
other side, yielding two (or more) subsets of data for each specimen. In
order to join the two landmark subsets into a common coordinate sys-
tem, it is necessary that a specific group of landmarks, visible from
both views, be collected from the specimen in both orientations along
with the set that can only be seen from one side. Once the data collec-
tion is complete, two subsets of data exist for every specimen, and each
subset includes a group (N 3) of shared or common points that are

recorded from both views. The two subsets are joined into a single,