3d Garment

3D GARMENT DESIGN AND ANIMATION –– A New Design Tool For The Garment Industry

Ying Yang, Nadia Magnenat Thalmann MIRALab, CUI Université de Genève 12 rue du Lac CH 1207 Genève Switzerland

Daniel Thalmann Computer Graphics Lab Swiss Federal Institute of Technology Lausanne Switzerland ABSTRACT Garment design is traditionally carried out in two dimensions, and some software has been developed and applied in the garment industry in the design of garment panels. In this paper, a new tool for the interactive design of garments in three dimensions is introduced. Making use of an elastic surface model, animation allows us to examine the garment design in three dimensions dynamically. The designer can use this tool to visualize his original ideas and changes interactively, and to see the garment vividly portrayed including texture mapping on the final design, before the real cloth panels are cut. Application of this tool in the garment industry could potentially reduce design time and costs substantially.

Keywords: cloth animation, garment panels, deformable models

2 1. INTRODUCTION As in many other industries, computers are being considered for use in the garment industry for both design and manufacturing. The traditional approach to garment making is first to take measurements of the human body, second to draw panel patterns on rectangular fabrics in two dimensions according to the style and fashion desired, then to cut the panels out, and finally to sew them together by hand or by sewing machines. Before the dress is sewn the tailor cannot know for sure what the dress will look like, and what the effect will be of wearing it on the human body. For a new fashion design, the tailor can only imagine the results, depending on his experience and talent. In recent years, computer technologies have begun to be used in the garment industry. Software has been developed and applied to the interactive design of 2D garment panels and to optimizing the layout of garment panels on the fabric. In Hinds and McCartney's work [2], a static trunk of a mannequin's body is represented by bicubic B-spline surfaces. Garment panels are considered to be surfaces of complex shapes in 3D. The garment panels are designed around the static mannequin body, and then are reduced to 2D cutting patterns. This approach is contrary to the traditional approach to garment design. The garment is modelled by geometric methods. To visualize the folds and drapes, harmonic functions and sinusoidal functions are superimposed on the garment panels. In Mangen and Lasudry's work [8], an algorithm is proposed for finding the intersection polygon of any two polygons. This is applied to the automatic optimization of the layout of polygonal garment panels in 2D rectangular fabrics. Both of these projects concern stages of garment design and manufacturing in real industrial contexts. Computer techniques of graphics offer many other possibilities for the development of high-tech tools for garment design and manufacturing. Not only can the interactive design of 2D garment panels be achieved by general computer graphics, but the sewing of garment panels and the examination of garment movement on the human body can also be visualized through cloth animation based on dynamic surface models. Terzopoulos et al. [9] and Aono [1] both proposed elastically deformable surface models to simulate and animate the movement of cloth in various physical environments. Another interesting approach by Kunii

3 and Gotoda [4] incorporates both the kinetic and geometric properties for generating garment wrinkles. Magnenat Thalmann et al. used a modified elastic model to create and animate various articles of clothing, such as a skirt, underwear, T-shirt and trousers, on a synthesized actor's body [6][7]. Based on the above techniques, we are developing a new design tool for use in the garment industry. This tool interactively designs the garment panels in 2D by computer, sews the garment panels in 3D on the computer screen, and dynamically simulates the garment's shape on the moving body of a synthesized actor. Texture patterns of various fabrics can be mapped onto the garment to make it look more realistic. The designer can modify the 2D panels if the 3D garment is not satisfactory. After all the examinations and changes, the final design is drawn by a plotter or is directly sent to a cutting machine which cuts the garment panels out of the fabric. A pattern library of garment templates can be connected to this tool. Adding A.I. techniques, it would be possible for the tool to automatically design garments for the public. In the following sections, the strategy and tactics of the tool are sketched out. 2.

A SYSTEM FOR INTERACTIVE GARMENT DESIGN The system for the interactive garment design tool consists of following five parts:

1) Interactive Graphic Interface for the 2D Design of Panels. 2) Deformable Cloth Model. 3) Pattern Library of Garment Templates. 4) Movable Human Body Model. 5) Output Interface.

The structure and the relationships of the system are as Fig.1

The interactive graphic design of the garment panels is carried out within the 2D design interface. With cursor movements of the mouse, the designer can draw and modify the patterns for the garment panels on the coordinate grid on the computer screen in two dimensions. The garment templates in the library can be loaded into the 2D design interface, so that they can be used or modified. The 3D human body model provides the movable

4 mannequin bodies and the motion sequences. Different sequences of human movements, such as walking, running, dancing, fashion modelling, and so on can be

generated. The 3D

deformable cloth model is used to create the garment from the fabric panels in three dimensions, and to simulate the changing shape of the garment on the mannequin as the body moves. Various properties of the cloth fabric, such as its mass, stretching and bending factor coefficients, damping density as well as characteristics of the physical environment, such as gravity and wind forces, are used to simulate the movements of the garment. In the template library, there are patterns of many different ruled or traditional garments. These templates can be used directly in the design or modified for the particular individuals. After the design is finally decided upon, the patterns for the panels in the final design are saved in the library. The patterns can be drawn on papers by a plotter or sent to the cutting machine to produce garment templates and the cloth panels.

3. 2D PANEL DESIGN The functions of the 2D panel design interface include mainly interactive drawing of the panel polygons, digitizing existing templates, and optimal placement of garment panels on rectangular fabrics of various sizes. Button positions, seam lines, and the sizes of the panels and garment, are also indicated on the patterns.

3.1. DIGITIZATION OF TEMPLATES Many templates already exist for various fashion styles of different peoples, for different body shapes, in different countries. They are the most valuable resources for the garment designer. Putting them in the template library is helpful in that the designer can easily access them and modify them slightly to make new garments. This requires digitalization of the existing templates. Only the tablet and mouse need be used to digitize the templates is polygonal sometimes with some curvilinear arc edges. The arc edges can be simplified to several terminal lines, so that all templates can be regarded as simply polygonals. With the tablet and mouse, starting at one vertex of the polygon, the shape of the garment can be

5 digitized into the library vertex by vertex. For curvilinear edges, additional points are chosen to be vertices.

3.2. INTERACTIVE PANEL DESIGN Less complicated than other CAD systems in mechanics or architecture, the interactive garment panel design is carried out in only two dimensions. Because all the panels can be simplified to polygons, the designer can easily create and modify their shape using general 2D interactive graphics. With the mouse and keyboard, the designer fixes vertex positions and inputs sizes, this creating the polygon. Buttons positions and seam lines are indicated within the panel polygons. If the designer is not satisfied with his work, he can modify his design in the same way.

3.3. LAYOUT OF GARMENT PANELS In the garment industry, most garment panels are not ruled polygons, the cloth fabric usually is rectangular and it comes in certain sizes only. It is important that the panels be laid out correctly on the rectangular fabric, otherwise much fabric will be wasted in the large-batch manufacturing of the garment. To optimize the layout of the panels, a simulated annealing algorithm [8] is used. First, all the panels are placed on the rectangular fabric arbitrarily, and the intersections of panel polygons are tested. If some polygons are overlap, they are moved apart; if the gaps between polygons are too large, they are moved closer. The testing and moving continues until the necessary length of fabric is obtained, without any superposition of panels is minimized. At this point, we also decide which panel edges will be seamed together , and which edges will be attached to the actor's body. For example, consider the geometric design of a T-shirt (Fig.2) and pants (Fig.3). The T-shirt and pants are very simple so each of them could be regarded as a single panel. As shown by Fig.2, the T-shirt is designed in a 2D rectangular mesh cloth ABCD by specifying the polygon's vertices v1,v2,v3, ...,v28. It is also specified that the edge v1v28 will be attached to the waist of the actor, and the edge v5v6 will be seamed with the edge v24v23, the edge

6 v11v12 will be seamed to v18v17, and the edge v5v6 seamed to v28v27. All the information, such as edge numbers of the polygon, the coordinates of vertices, which edge will be seamed and attached, etc. are stored in the data structure of the panel. The 2D polygonal cloth panel will be transferred into 3D polygonal panel in ruled surfaces. 4. THE DEFORMABLE CLOTH MODEL AND ITS PARAMETERS To simulate the sewing and animation of the garment, deformable cloth models must be used. Physically-based models are preferable in the hopes of increased realism. This should take into account such physical properties as mass, stiffness, damping factors, inhomogeneity, anisotropy and viscoelasticity. The model should be deformable under external forces and its own internal elastic energy, should detect collisions of the cloth with itself and with external objects, and should be able to create constraint forces when collisions occur. With this model, diverse kinds of clothing can be created and animated by defining and adjusting the geometric sizes, the physical properties of cloth and the external forces applied to it. After some comparisons [7], Terzopoulos' elastic surface model [9] was chosen for our system. In this model, the main parameters are as follows: • • • • • • • •

mass density of the nodal point of the fabric. damping density of the fabric. stretching coefficients of the fabric. bending coefficients of the fabric. gravity. external forces, including wind force, collision forces, etc. time step for calculating the deformation. number of relaxation steps.

These parameters are determined by the physical properties of the fabric. Different fabrics have different physical properties. For example, silk is hard to stretch but easy to bend, woolen cloth is more massive and rigid. When worn on the human body, garments with the same polygonal panels but different fabrics will take on different shapes. The environmental factors, such as gravity, wind forces, and collision forces also affect the shapes of the garments, and they can be changed dynamically to examine the environments.

garment under various

7 The most useful parameters for modifying the appearance of the motion are the density, the damping factor, resistance coefficients, the wind and the time interval.

5. SEWING GARMENT PANELS IN THREE DIMENSIONS Once the desired panels are designed, they are sewn along the indicated seam lines around the mannequin's body in 3D making use of deformable cloth model. At this stage, the mannequin's body is static in a standing posture, and gravity is the single environmental factor. The garment panels are first placed around the mannequin's body, then external sewing forces are applied to the indicated seam lines shown on the panels.

These sewing forces gradually

deform relaxation step and time step. Collisions among the different parts of the garment are detected and repulsive forces are applied between any two parts of the garment in contact. When the panels are close enough to the mannequin's body, a collision between the garment and the body will occur. The body creates the repulsive forces to beep the garment outside the body [5]. Spring forces are used to simulate the repulsive force. When the seam lines are all sewn up and the deformation of the garment is complete, the 3D garment has been created (Fig.4). Some special features of garment, such as wrinkles (Fig.5), folds, and drapes, are automatically calculated and formed by the deformable cloth model. Texture mapping can also be applied to the garment, so that it will look more realistic as shown in Fig.6.

For example, as shown in Figure 7, we create a T-shirt and pants in the 2D plane and transfer them into 3D space around Elvis' body. During the seaming and attachment procedure, the edges of both the T-shirt and the pants near the body's waist are attached to the waist, the four edges of the T-shirt near the shoulders are seamed together, and the two bottom edges of the pants are seamed to each other. As the result, a suit of clothes including article 1, the Tshirt, and article 2, the pants, has been designed and fabricated. Fig.8 and Fig.9 shows examples. In the same way, Fig. 10 shows a dress and Fig. 11 shows a view of Marilyn wearing this dress.

8 6. GARMENT ANIMATION WITH HUMAN BODY MOVEMENT Garment animation during human body movement is performed by the deformable cloth model and the human body model. First, a series of sequences of human body movement, such as walking (Fig.12), running, dancing, jumping, fashion modelling etc. are generated by the human body model. When the mannequin is moving, collisions between different parts of the garment itself, and between the garment and the body are tested and repulsive forces are automatically calculated and applied. Environmental factors, such as gravity, variable wind forces, air viscosity, are added to deformable cloth model. The sewing forces assure that the panels remain joined together. With the movement of the body, the shape of the garment, including wrinkles, folds, drapes, is changed automatically. The parameters of both the fabric and the environment, can be adjusted flexibly.

7. GARMENT EXAMINATION AND CHANGE During the procedures of sewing and animation of the garment, the designer checks the appearance of the garment in three dimensions. If the result is not satisfactory,

he can

interactively modify the shapes of panels, or the parameters corresponding to the fabric's properties, as well as the factors of the environment. The animation is repeated and the whole process is iterated until the desired effect is obtained.

8. IMPLEMENTATION 8.1 Data structures At the present stage of development of the garment design tool system, the human body model and deformable cloth model have both been completed. The 2D interactive design interface for the garment panel and the template library are still under development.

The clothes on the actor's body may include several articles, such as T-shirts, pants, jackets and trousers, and each article may consist of several cloth panels, so the data structure of clothes in the software is hierarchical, as shown in Figure 13.

9 In this cloth data structure, the seaming information between panels or within the panel itself, and the information about attaching each article to actor's body is also included. The panel is the elementary unit treated by the elastic surface model. In a panel data structure, there are geometric data and physical data, seaming information and attaching information, as shown in Figure 14. The geometric data about a panel include the polygons' edge numbers, the polygons' vertices, the number of points in the mesh panel, the center of the panel and its rotating angle, etc. From the geometric data on a panel, we can derive its shape, size, position, normal, and so on. The physical data on a panel include its mass, the damping factor, speed, forces on it, the stretch factor, the curvature factor, elastic energies (the stretch energy and curvature energy), etc.. The seaming information for one panel concerns which edges of the panel should be seamed together. It includes the number of nodes on the edges and the coordinates of the nodes in the 2D mesh plane, and indicates which node is seamed to which. The attachment information indicates which edges of the panel are attached to specific points on the actor's body. It includes the number of nodes on the edges and the coordinates of the nodes in the 2D mesh plane, and indication of which one node is seamed with which point on the actor's body. An article of clothing consists of several panels seamed together, so its data structure contains the panel data and the information about seaming the panels, together, shown in Figure 15. The texture mapping approach is also being worked out. For the moment, WAVEFRONT software is used to put the texture pattern on the garment.

8.2 Collision detection When we consider collisions between the cloth and the body, we have a situation of actorenvironment interface using a physical motion control method. Collision detection adds extra

10 constraints and requires a specific algorithm. For very flexible objects like clothes, it is necessary to introduce a self-detection. In our method [5], collision avoidance consists of creating a very thin force field around the obstacle surface to avoid collisions. This force field acts like a shield rejecting the points. The collision detection process is almost automatic. The animator has only to provide the list of obstacles to the system and indicate whether they are moving or not. For a walking synthetic actor, moving legs are of course considered as a moving obstacle. A number of parameters have been planned in order to modify the behavior of the collision detection method: shield depth, shield force and damping factor. As the algorithm speed depends on the number of obstacle polygons, it is prudent to take into account only polygons which are likely to intersect the cloth. For the example of Marilyn's skirt, only the pelvis and the legs are considered (Figure 16-17). With this method, we created and animated flags in the wind and a skirt (Fig.18) in the computer-generated film Flashback (Fig.19-20).

8.3 Methodology of use To use this new tool in garment design, the procedure consists of the following steps: 1. Take the measurements of the human body. 2. Interactively draw the polygonal patterns of the garment panels or select the templates from the garment template library. 3. Modify the shapes of the garment panels. 4. With the deformable cloth model and the human body model, create the garment on the mannequin body in three dimensions. 5. Simulate and animate the changing shape of the garment with moving sequences of the mannequin's body. 6. Examine the changing shape of the garment to see if it is satisfactory or not. 7. If the garment is not satisfactory, do (3) to (6) again. 8. Save the patterns in the garment template library.

11 9. Draw the patterns of the garment panels on paper. The above steps illustrate the superiority of this tool over the traditional design approach. The designer can dynamically visualize his design before the garment is actually made. Much time and cloth can therefore be saved.

9. CONCLUSION Using new animation techniques, we are developing a high-tech CAD tool for garment design. This tool not only designs garment panels in 2D, but it also allows the visual examination of the garment in 3D on a moving human body with cloth animation, before the garment is actually manufactured. This improves on traditional garment design which is only carried out in two dimensions, and makes the design process more convenient and economical.

Acknowledgements The research is partly supported by the Fonds National Suisse de la Recherche Scientifique, le fonds FCAR du Québec and the Natural Sciences and Engineering Research of Canada. The authors would like to thank Arghyro Paouri for the design of several pictures. References 1. Aono M (1990), A Winkle propagation Model for Cloth, Computer Graphics Interface, springer 90, Singapore, pp.96-115 2. Hinds BK, McCartney J (1990) Interactive garment design, The Visual Computer, 6, pp.53-61 3. Platt JC, Barr AH(1988) Constraints Methods for

Flexible Models, Proc.

SIGGRAPH'88, Computer Graphics, Vol.23, No.3, pp.21-30 4. Kunii TL, Gotoda H (1990) Modeling and Animation of Garment Wrinkle Formation Processes, Proc. Computer Animation'90, Springer, Tokyo, pp.131-147 5. Lafleur B, Magnenat Thalmann N, Thalmann D (1991) Cloth Animation with SelfCollision Detection, in: Modeling in Computer Graphics, edited by TL Kunii, SpringerVerlag, Tokyo, pp.179-188

12 6. Magnenat Thalmann N, Yang Y (1991) Techniques for Cloth Animation, in: New Trends in Animation and Visualization, edited by N. Thalmann and D. Thalmann, by John Wiley & Sons Ltd., pp.243-256. 7. Magnenat Thalmann N, Yang Y, Thalmann D (1991) The Problematics of Cloth Animation", Proc. of 2nd Conference on CAD/CG, International Academic Publishers, Beijing, China, pp.1-7. 8. Mangen A, Lasudry N (1991) Search for the Intersection Polygon of any Two Polygons: Application to the Garment Industry, Computer Graphics Forum 10, pp.19-208 9. Terzopoulos D, Platt J, Barr A, Fleischer K (1987) Elastically Deformation Models, Proc. SIGGRAPH'87, Computer Graphics, Vol. 21, No.4, pp.205-214

13 2D Design Interface

Garment Template library

Output Interface of Design

3D Examination

3D Deformable Cloth Model

3D Human Body Model

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A suit of clothes article 2 article 1

... article m panel 1 ... panel n2 panel 2

panel 1 ... panel n1 panel 2 point 1

... point k1

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panel 2 ... panel n3 panel 1

15 panel

geometric data: polygon's edge numbers, polygon's vertices, mesh nodes' positions,...

physical data: mass, damping factor, speeds, forces, stretch factor, curvature factor,...

seaming information: edge x1 seamed with edge x2, edge x3 seamed with edge x4,...

attaching information: edge y1 attached to edge z1 on the body, edge y2 attached to points z2 on the body,....

article panel data: number of panels, series of panels

seaming: edge x1 of y1 seamed with edge x2 of panel y2, edge x3 of panel y3 seamed with edge x4 of panel y4, ...

16 Figure captions Fig.1. Structure and relationships of the system Fig.2. Geometric Design of T-shirt Fig.3. Geometric Design of Pants Fig.4 An example of 3D cloth Fig.5 Cloth with wrinkles Fig.6 Texture mapping Fig.7 Seaming clothes and putting them on Elvis Fig.8 Putting a pant on Marilyn Fig.9 Marilyn wearing a T-shirt and a pant Fig.10 A dress for Marilyn Fig.11 Marilyn wearing a dress Fig.12 Clothes animation in Marilyn's walking sequence Fig.13. The hierarchical data structure of clothes Fig.14. The data structure of a panel Fig.15. The data structure of an article Fig.16 a-b Skirt animation Fig.17. A scene from the film Flashback Fig.18. A scene from the film Flashback Fig.19. A scene from the film Flashback

17 Ying Yang is a PhD student at MIRALab, University of Geneva. He received his MSc in CAD/CAM from Beijing University of Aeronautics and Astronautics. His research interests include three-dimensional computer animation and geometric modeling. E-mail: [email protected] Nadia Magnenat Thalmann is currently full Professor of Computer Science at the University of Geneva, Switzerland and Adjunct Professor at HEC Montreal, Canada. She has served on a variety of government advisory boards and program committees in Canada. She has received several awards, including the 1985 Communications Award from the Government of Quebec. In May 1987, she was nominated woman of the year in sciences by the Montreal community. Dr. Magnenat Thalmann received a BS in psychology, an MS in biochemistry, and a Ph.D in quantum chemistry and computer graphics from the University of Geneva. She has written and edited several books and research papers in image synthesis and computer animation and was codirector of the computer-generated films Dream Flight, Eglantine, Rendez-vous à Montréal, Galaxy Sweetheart, IAD and Flashback. She served as chairperson of Graphics Interface '85, CGI '88, Computer Animation '89 and Computer Animation '90. E-mail: [email protected] Daniel Thalmann is currently full Professor and Director of the Computer Graphics Laboratory at the Swiss Federal Institute of Technology in Lausanne, Switzerland. Since 1977, he was Professor at the University of Montreal and codirector of the MIRALab research laboratory. He received his diploma in nuclear physics and Ph.D in Computer Science from the University of Geneva. He is coeditor-in-chief of the Journal of Visualization and Computer Animation, member of the editorial board of the Visual Computer and cochairs the EUROGRAPHICS Working Group on Computer Simulation and Animation. Daniel Thalmann's research interests include 3D computer animation, image synthesis, and scientific visualization. He has published more than 100 papers in these areas and is coauthor of several books including: Computer Animation: Theory and Practice and Image Synthesis: Theory and Practice. He is also codirector of several computer-generated films. E-mail: [email protected]