Biology Reference
In-Depth Information
One method for superimposing semilandmarks, suggested by
Sampson and colleagues
(1996)
, slides semilandmarks to the position that minimizes the summed squared deviations
between each individual and the reference form. The semilandmarks are not free to move in
any direction; each is confined to slide along the line tangent to the curve at that semiland-
mark (
Figure 3.10
). The shape of the curve is not actually known, so the tangent is estimated
as the line parallel to the segment connecting a series of adjacent landmarks
or semilandmarks. Each semilandmark of the target slides along its tangent to align with
the perpendicular at the corresponding semilandmark of the reference. Using this method,
FIGURE 3.10
Semilandmark superimposition. (A)
Landmarks (black) and semilandmarks (white) on a squirrel
scapula; (B) finding tangents to the curve and sliding
semilandmarks.
FIGURE 3.11
Semilandmark superimposition
result. (A) Landmarks (black) and semilandmarks (hol-
low) on a squirrel scapula; (B) slid semilandmarks.
