New VR technologies have been developed,
which form the basis for a realistic, three dimensional, (real-time)
simulations and visualisation of individualised garments put on by virtual
counterparts of real customers, reveals O L Shanmugasundaram.
Clothing manufacturers require systems
with the capacity to deal with garment design process as a whole, including
possibilities to work directly within a 3D graphic environment. In such a
context, the aim of the author's research work has been the development of a
graphic and interactive environment to design men garments and simulate
their behaviour according to fabric properties and manufacturing processes.
The system should permit to predict the real garment
behaviour acting on the parameters characterising its physical model in
order to reduce the number and the role of the physical prototype.
This kind of tool is not to be confused
with other research prototypes or systems currently available on the market
(eg, MAYA? Alias/Wave front), since they are mainly oriented to animation
and applications, such as movies, cartoons, or virtual catwalks. Figure 1
shows the reference architecture of a 3D system for garment design and
simulation. One can distinguish two modi operandi according to garment
types, design process, and strategies adopted within manufacturing
The first one involves drawing 2D
patterns by using 2D CAD systems. Modules have to be developed to generate,
starting from 2D patterns, data necessary to define the 3D physical model of
the garment and execute the simulation. The latter, more innovative,
consists of the design of 3D garments around a digital mannequin. This
technique is more natural and creative, because it allows direct
transference of the garment concept.
The mode list uses 3D graphic tools, the
3D Modeler and the 3D Simulator, to both design and simulate the garment.
The 2D patterns are automatically generated as well as data for assembling
and positioning 2D patterns around the mannequin to define the physical
model. The author followed the second approach, even if different solutions
have to be adopted for men and women garments.
In the course of the project Virtual
Try-On, innovative VR technologies have been developed, which form the basis
for a realistic,
three-dimensional, (real-time) simulation and visualisation
of individual customers and garments. Utilising these VR techniques, an
integrated virtual shop infrastructure is provided, which facilitates the
presentation and trade of individualised garments at the point-of-sales and
soon over the Internet. Instead of replacing the current shopping experience
(eg, really touching garments and materials), Virtual Try-On, in fact, aims
at enhancing customer support and decision making through extending
corresponding customer services.
The following scenario describes a
typical way a customer will experience the VTO shopping environment at the
point of sales.
There are basically two methods for the
simulation of cloth: Geometrical models and physically-based models.
Physically-based Cloth Simulation in
Virtual Reality (WSI/GRIS)
The physically-based cloth simulation is
responsible for sewing the pre-positioned garments along the seam lines and
for computing the drape of the clothes on the avatar. For Physical Model and
Numerical Solution to compute realistic animations of clothes, the author
developed an efficient model based on finite elements for viscoelastic,
highly flexible surfaces. It is particularly designed for numerically stiff
materials such as textiles because it yields linear equations in each time
step and allows fast time stepping in an implicit integration method. This
is achieved by reducing the nonlinear elasticity problem to the planar,
linear case in each step.
With this model, one can assemble
garments from CAD cloth patterns, seam these together, and animate the cloth
in dynamic scenes with any
chosen material properties (see Figure 10). This
results in a physically accurate and also fast simulation. The basic idea in
this approach is to use a linear strain formulation and to construct a
rotated rest state for each element. The arising ordinary differential
equations time are solved by an implicit Euler method.
Textiles show very different physical
behaviour in weft and warp directions, so we model elastic and viscous
material parameters for the two directions independently. Material
measurements are carried out with the Kawabata evaluation system for the two
Young moduli, the shear modulus and the Poisson number, which controls the
transverse contraction. Additionally, the bending moduli describe the
curvature elasticity in the weft and warp directions. In order to model the
exact hysteresis effects of the corresponding tissue, dynamic material
parameters are measured with the Kawabata and Zwick systems.
Geometric modeling of garments
As pointed out, the standard way of
designing realistic virtual simulations begins with the definition of all
the necessary 2D fabric patterns, thus requiring knowledge of tailoring that
is not necessarily possessed by most computer artists. The users then need
to specify sewing constrains for the patterns. This tedious process is made
even more complex by the need to set adequate values for a set of physical
parameters and run a simulation to obtain the final shape for the garment,
even then the character is at rest.
The alternative is to model the garments
directly in 3D, as proposed by, who developed a sketch based garment
modeling tool. However, using direct modeling in 3D, the generated shape is
typically not piecewise developable, and thus depicts a garment, which is
not physically plausible. Moreover, the modeled garment is unlikely to
depict fold patterns specific to real garments in any rest position. The
author's work enhances this alternative approach by making it usable as a
starting point for modeling the static shape of realistic garment. In
particular this method approximates the garment surface mesh obtained from
mask etch by a piecewise developable surface.
The developed system
1. The 3D Modeler that possesses all the
necessary functionality to edit (Editor Module) men garment according to
traditional designer's working method and to automatically generate (Export
Module) data for 2D patterns representation, necessary for garment
simulation and manufacturing.
2. The 2D CAD system used to produce,
using above mentioned data, the 2D patterns of the 3D designed garment.
3. The 3D Simulator that consists of
three main modules: The Module to generate physical model for defining the
particle model of 2D panels according to fabric properties, the Module to
assemble patterns for sewing and assembling 2D patterns over the mannequin (ie,
the initial 3D configuration), and, finally the Solver for executing the
4. The User Interface that proposes a
unique environment for both the Modeler and the Simulator. It has been
designed to be as close as possible to traditional design process and based
upon the designer's knowledge.
The design process, currently followed
within companies, has been analysed in order to extrapolate functionalities
of the Modeler. As reference
garment, we selected a jacket since it is
considered the most representative men cloth. Typically, the designer
creates a new style by modifying the shape of a physical prototype, eg,
changing sleeves length or tightening the waist, according to fashion trends
and stylist's sketches. To do this, the designer uses reference elements:
Sewing lines, significant and structural elements, such as waist or
Therefore, the Modeler had to permit the
designer to operate in the same way using a digital prototype instead of a
physical one. This required the acquisition of the mannequin and jacket
geometry to be used as reference shape from which derives new ones by
interactive changes. The Editor Module has been implemented using and
combining MAYA Deformers [Maya00], which enable the user to change the shape
of a geometric model. From the analysis of modelist's modus operandi, the
author have identified and implemented a set of modifiers that permits the
designer to perform traditional modifications. Some examples are:
Shorten/lengthen sleeves, tighten/enlarge shoulders, tighten/enlarge waist,
shorten/lengthen jacket. For each type of modifier, we have identified the
interaction style and allowable range of values.
As already said the 3D simulator is
based upon the particle-based approach. As shown in Figure 2, it possesses
all the necessary functionality to: ?
Import the mannequin used by the
modelist to design the 3D garment.
Automatically generate the particle
model of 2D panels according to material properties.
Position and assemble 2D patterns
over the mannequin using data generated by the 3D Modeler and acquired
Execute the simulation.
The prototype proceeds according to the
1. 2D garment patterns are discretised
according to the particle-based approach and warp-weft directions.
2. Forces among particles and
corresponding parameters value are established on the basis of fabric
3. 2D patterns are sewed using reference
lines and assembled over the mannequin in order to reach an initial
4. Garment's behaviour is simulated.
Real-time animation of garments
The real-time animation has been
integrated into the garment design tool to provide a preview of the clothes.
Imated body and a garment whose rest shape has been computed with the
garment design tool, this module provides the real-time visualisation of the
garments on the animated body. This module can be used at anytime during the
making of the clothes helping the designers to judge the quality of their
Simulating garments in real-time
requires drastic simplifications of the simulation process to be carried
out, possibly at the expense of mechanical
and geometrical accuracy. The
approach, described by Cordier et al, is based on a hybrid method where the
cloth is segmented into various sections where different algorithms are
When observing a garment worn on a
moving character, the authors notice that the movement of the garment can be
classified into several categories depending on how the garment is laid on,
whether it sticks to, or flows on, the body surface. For instance, a tight
pair of trousers will mainly follow the movement of the legs, whilst a skirt
will flow around the legs. Thus the authors segment the cloth into three
layers that we define as follows (Figure 11):
Layer 1 (Stretch cloth): Garment
regions that stick to the body with a constant offset. In this case, the
cloth follows exactly the movement of the underlying skin surface.
Layer 2 (Loose cloth): Garment
regions that move within a certain distance to the body surface are
placed in another category. The best examples are shirtsleeves. The
assumption in this case is that the cloth surface always collides with
the same skin surface and its movement is mainly perpendicular to the
Layer 3 (Floating cloth): Garment
regions that flow around the body. The movement of the cloth does not
follow exactly the movement of the body. Collisions are not predictable;
For a long skirt, for instance, the left side of the skirt may collide
with the right leg during animation.
These three categories are animated
using three different cloth layers. The idea behind the proposed method is
to avoid the heavy calculation of physical deformation and of collision
detection wherever possible, ie, where collision detection is not necessary.
The main interest of the approach is to pre-process the target cloth and
body model so that they are efficiently computable during runtime. The
garments are divided into a set of segments and the associated simulation
method is defined for each.
The segmentation process dispatches each
garment region to its adequate layer. From the garment in its rest shape on
the initial body, the distance between the garment and the skin surface is
used to determine to which category the cloth triangles belong. Associated
with each segment are distances from the skin surface that are used to
determine the category. Each segment falls into one of three categories:
Tight, loose and floating clothes. Cloth vertices that are located closely
to the skin surface belong to the first or the second layer. Cloth vertices
that do not collide with any skin surface belong to the third layer.
The techniques for real-time clothes
simulation are proposed. Garment vertices are animated with three different
methods, depending on which layer they belong that is defined during the
pre-processing stage. Tight clothes in Layer 1 follow the deformation of the
underlying skin. These deformations are calculated thanks to the mapping of
the attachment data of the skin to the garment surface.
For Layer 2 that is composed of loose
clothes, the relative movements of clothes to the skin remain relatively
small, keeping a certain distance from the skin surface. Consider the
movement of sleeve in relation with the arm: For a certain region of the
garment, the collision area falls within a fixed region of the skin surface
during simulation. With this in mind, the scope of the collision detection
can be severely limited.
A basic assumption made is that the
movement of the garment largely depends on that of the underlying skin and
yet it should not follow the skin surface rigidly. It is necessary to
simulate the local displacement of the garment from the skin surface. Two
different methods have been developed; One for cloth deformation on the
limbs (trousers and sleeves), and the other one for the deformation of cloth
on the trunk.
Cloth vertices on the limbs are enclosed
in half spheres that are attached to the skin surface. Vertices inside these
spheres are displaced with the equation of the rigid body motion. A function
defines the diameter of the spheres depending on the relative position of
the cloth vertex to the normal of the skin surface. Cloth vertices located
on the trunk are animated with a rough mesh. This rough mesh is animated
with a physic-based method. The cloth mesh is deformed with the FFD method
using the position of the vertices on the rough mesh (Figure 13).
Layer 3 is composed of vertices that
freely float around the body. This will take care of cases, such as a large
skirt floating around the legs. Any part on this skirt can collide with any
part of the leg. Downloaded from the Web server, the Web Client application
contains the body/garment sizing module and the real-time garment simulation
module. The body/garment sizing module provides functionalities to deform
the 3D mannequin from the customer's input body size and resize the selected
garment accordingly. Once the garments and the mannequin have been adapted
to the customer's measurements, the animation of the dressed mannequin is
taken care of by the real-time garment simulation module. The simulation of
this layer uses a classical approach with particle system and collision
Some visual results obtained using the
system are presented in this section. Figure 6.1 shows a woven cloth
emphasising the difference between the front and back sides. Figure 6.2
shows the deformation of the loops of a knitted cloth. Limitations and
Dynamic animation of garments was
outside the scope of this paper. However, Virtual Garments: A Full Method
could be used in two different ways toward this goal. The 2D patterns that
is generated can be used by a cloth animation system to compute the rest
lengths of the springs that model the cloth material. Thus, the garments
designed can be animated using standard techniques.
Another option would be to take
advantage of the procedural modeling of fabric folds during animation. Then,
only the control mesh would need to be animated using physically-based
simulation, while fine details such as folds, are costly to simulate. They
are caused by stiff, buckling phenomena would be added procedurally at no
cost prior to rendering. The author plan To explore this approach in the
Another possible application of the work
is the prototyping of real garments. A fashion designer could use the
sketching system to quickly sketch some clothing, automatically get
different 3D views of the garment, edit the model as necessary, and finally
print the corresponding 2D patterns. This would require a number of
enhancements to the method, such as introducing gussets and enabling axial
An efficient technique for cloth
simulation has been presented. It uses a mass-spring model with velocity and
force modification methods for coping with the super-elasticity and for
resolving responses to collisions. As a result, the speed is good enough for
almost real time simulation of draping virtual garments on animated virtual
humans. The body surface is acquired through a 3D scanner, which makes the
approach very accurate and allows users to try on different sizes of
clothing and see how they fit them. So far the author conducted experiments
on static and very crudely animated human bodies. Future plans are to
implement dynamic simulation of garments on naturally animated virtual
actors using the presented approach. Animation will be done by applying
motion tracker data and skin deformation techniques to the static body. The
author will evaluate the efficiency and compare it to existing techniques.
O L Shanmugasundaram. Lecturer with
the Department of Textile Technology, K S R College of Technology,
Tiruchengode, Tamil Nadu 637 215.