Page 367 - Anthropometry, Apparel Sizing and Design

Sizing and fit for pressure garments 359

(1) an inclusion of special procedures in a flattening algorithm;
(2) a transformation of pattern blocks taken from an avatar on the 2D surface after flattening
(Ziegert and Keil, 1988; Watkins, 2011);
(3) flattening of the 3D surface which has “negative ease” compared to the surface of
the avatar.
The existing implementations of the first approach don’t consider the anisotropic
properties of textile materials and require special software.
The second approach, as a kind of traditional method to design the basic blocks, is
not appropriate for 3D design.
The third approach is based on the creation of a compression garment surface in a
form appropriate for 3D-to-2D flattening of its parts. For its implementation, it is nec-
essary to build a 3D model of the compression garment in a “relaxed state” (when the
shell of the garment is not elongated and locates inside the avatar), and then to gen-
erate its flattened pattern blocks. The technical capability of constructing and flatten-
ing the parts of a 3D garment with “negative ease” exists in CAD LooksTailorX.
However, the body measurements taken from the typical solid avatar that presents
the standard body might be not enough to create a more complex and realistic pressure
profile. Besides, there is no opportunity to calculate an ease based on the requirements
of pressure comfort. The 3D shape of the compression garment based on the cross-
sections of the human head and pressure comfortable data can be calculated
(Balandina, 2007).
The most convenient and common way of representing the surface of 3D virtual
garments is a polygonal mesh. It allows reproduction of complex surface topography
and achieving of a high accuracy level of the shape. There are two main methods for
flattening of 3D polygonal mesh objects: physical and geometrical. The physical
method is based on the calculation of minimal tension energy of the deformable ele-
ments of the polygonal net; the advantages of deformable elements are an isomor-
phism and an allowance for the anisotropic properties, but elements are iterative
and may be unstable (Hsiao, 2014; Liang and Bin, 2004; Wang et al., 2002; Li
et al., 2005; Zhang and Luo, 2003).
The geometrical method is based on geometrical values of deformable elements,
such as edge lengths, angles, areas of faces, etc. (Wang and Tang, 2010; Sheffer
et al., 2005; Azariadis and Aspragathos, 2001). Geometrical constraints help to deter-
mine proper positions of mesh vertexes.
Usually, the methods for calculating the pattern blocks of garments made of knitted
materials are physical or combined and give an opportunity to directly use the equa-
tions for tensile force and strain of real materials.
Most CAD applications allow 2D-to-3D virtual try-on, so the generated pattern
blocks could be used for virtual simulation, such as stitching of the parts and dressing
the garment on the avatar (Browswear, n.d.; Lectra Modaris 3DFit, n.d.; Optitex 3D
Runway, n.d.).
According to Eq. (13.1), the tensile force determines the pressure on the body, at
the same time, the extensibility of the textile material must correspond to the garment
pressure. The appropriate range of knitted fabric deformation can be calculated by the
function σ ¼f(ε)(Ibrahim, 1968). Since the materials for compression garments