3.4. 2D cross sections of each 3D image
The last step in our data preprocessing procedure is to obtain
the 2D cross sections of each 3D aligned shape. Six main cut points
which have been marked with arrows in Fig. 3 are determined
along the trunk of the women, which are arbitrarily numbered as:
1. crotch height (H1)
2. height of the lower waist markers (average of both sides) (H2)
3. height of the upper waist markers (average of both sides) (H3)
4. height of the section where the breasts are more prominent
(horizontal distance between chest and back is maximum) (H4)
5. armpit level (average of both sides) (H5)
6. height of the neck marker (H6)
To be able to compare different shapes in a meaningful way we
extracted 100 slices from the trunk section. These will be distributed
as follows:
Between points...
1–2 2–3 3–4 4–5 5–6
Number of extracted sections 35 5 20 5 35
The total number of slices (100) was taken so that they are close
enough to represent appropriately the details of the shapes still
keeping a reasonable computational cost. The number of slices in
each section is taken approximately proportional to the average
thickness of such section. This results in a real separation between
slices different for each women, but only slightly different for
women belonging to the same group of those we take for the study
(see Table 1). By doing this we can establish a correct homology
between shapes of different heights taking into account anatomical
information. From now on we will denote zij as the Z-coordinate of
section j of woman i, where j ¼ 1 ... 100.