Pillow: Interactive Flattening of a 3D Modelfor Plush Toy Design
Yuki Igarashi1 and Takeo Igarashi21

The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, 153-8904, Japanyukim@acm.org
http://www.den.rcast.u-tokyo.ac.jp/∼yuki
2
The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan

Abstract. Pillow is an interactive pattern-design system for creatingplush toys. The user imports a 3D surface model into the system andspeciﬁes the segmentation boundaries interactively by drawing seam lines
on the model surface. Based on this segmentation, the system generates
a 2D pattern by ﬂattening each outlined region, and then visualizes theshape of the resulting plush toy by applying a simple physics simulation.
If the result is not satisfactory, the user can make diﬀerent seam lines.
This closed-loop framework allows users to experiment with various seam
patterns before actually working on real fabric to obtain the best-looking
result. The system also estimates total sewing time based on the total
length of the seam lines. We implemented the system to produce plush
toys and a balloon.

1Introduction

To design an original plush toy, one needs to construct an appropriate 2D patternwhich is very diﬃcult. For this reason, all existing patterns have been developedby professional designers. To enable people to design their own original plush
toys and similar products, we developed an interactive pattern-design system.
Called Pillow, the system allows users to import a 3D model and interactively
specify segmentation boundaries by drawing seam lines on the model surface.
The system generates 2D patterns by ﬂattening the user-deﬁned segments andthen simulates the shape of the plush toy. If the simulation is not satisfactory,
the user can try another set of seam lines. This closed-loop interaction allows one
to experiment with various seam line designs without actually sewing real fabric.
The system makes it easier to construct 2D patterns, and allows users to design
their own original plush toys and other products. The system also estimatessewing time based on the total length of seam lines. We produced some plush
toys and a balloon using the system, and discuss the results below.
Mori and Igarashi [1] presented an interactive system that allows nonprofessional designers to develop their own original plush toys. The user interactively
designs a 3D model by a sketching tool, and then the system generates a corresponding 2D pattern. However, the system is not useful when the user alreadyhas a 3D model. Julius et al. [2] presented an automatic segmentation algorithm
A. Butz et al. (Eds.): SG 2008, LNCS 5166, pp. 1–7, 2008.
c Springer-Verlag Berlin Heidelberg 2008
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Y. Igarashi and T. Igarashi

for plush toys and demonstrated its viability by creating real toys using themachine-generated pattern. However, their method relies on purely geometriccriteria, and it is diﬃcult to capture the perceptually important features of theoriginal shape. As a result, seams can appear in undesirable areas, such as acrossthe face of a toy, or in ways that ignore the symmetry of the model. Our approach focuses on the user’s artistic process of pattern design and provides tools
to support the exploration process.

2User Interface

Figure 2 shows a snapshot of the system. The left window shows the original 3D
model, the center window shows the ﬂattened 2D pattern, and the right windowshows the reconstruction. Users import a 3D surface model (Fig. 1(a)), uponwhich they draw free-form lines to mark segmentation boundaries (Fig. 1(b)).
These can be erased if necessary, Once all the segments are outlined, the system

(a)

(b)

(c)

(d)

(e)

Fig. 1. Illustration of the Pillow system. (a) Input 3D model, (b) seam lines drawn
by the user, (c) 2D sewing pattern generated by ﬂattening the digitized regions, (d)reconstruction generated by applying a physics simulation to the pattern. The user
repeats (b) through (d) until obtaining a satisfactory result. (e)The ﬁnal product.

(a)

(b)

(c)

Fig. 2. A screen snapshot of the Pillow system

Pillow: Interactive Flattening of a 3D Model for Plush Toy Design

(a)

(b)

3(c)

Fig. 3. Segments joined using connectors (b) and numbers (c)Fig. 4. Example of pattern designs

automatically ﬂattens them (Fig. 1(c)) and reconstructs the 3D geometry by
virtually sewing all of the ﬂattened pieces together and applying a simple physics
simulation (Fig. 1(d)). This view represents how the stuﬀed toy might look whena real toy is created using the current segmentation. If the user dislikes the result,
he can quickly change the segmentation by erasing and redrawing the seam lines.
The system displays how patches are joined by showing connectors or paired
numbers (Fig. 3). Connectors are useful for understanding the relationship on thescreen and numbers are useful as a printed reference on each patch. The systemprovides an automatic layout and manual arrangement interface for preparing
the ﬁnal pattern to be printed.
Figure 4 shows examples of pattern designs. Users can quickly experimentwith various segmentation strategies using the system, and the simulation results
successfully capture the overall shape of the ﬁnal sewing results.

43Y. Igarashi and T. Igarashi

Estimation of Total Sewing Time

Total sewing time diﬀers depending on the design as shown in Table 1, and it isvery helpful to know how long it will take to create a plush toy during the designphase. To achieve this goal, our system automatically estimates total sewing timeand presents this information to the user during seam design. It is assumed thatthe user will sew the pattern by hand.
Table 1. Geometric values of the 2D patternFig. 4(top)Fig. 4(bottom)

3.1

Time(min) Lseam Nseam
402756.5 16683706.3 38

Classification of Time Costs

Four main factors, or costs, determine the time required to create a plush toy:
cutting a printed pattern (Ccut ), tracing the pattern boundary on the cloth(Ctrace ), cutting the cloth (Ccut cloth ), and sewing the cloth (Csew ). The cost ofstuﬃng is ignored because it is negligible compared to the sewing time. Therefore,
the total cost (Ctotal ) to create a real plush toy is deﬁned as:
Ctotal = Ccut + Ctrace + Ccut cloth + Csew .

(1)

The cost of cutting a pattern (Ccut ) has already been explored by Mitani[3]. We approximate Ctrace and Ccut cloth by using Ccut because all operations
essentially trace the same seam lines on the 2D pattern. The total cost is written
as follows:(2)
Ctotal = 3Ccut + Csew .
Cutting Cost: Mitani [3] computed the cost of cutting a pattern as follows:
Ccut = Wcut Lseam + Wcut stoit Ncut stoit ,(3)where Lseam is the length of the seam line, Wcut is the weight per unit Lseam ,Ncut stoit is the number of stoit points where the scissors turn, and Wcut stoit is
the weight per stoit point. We use the weights Wcut = 1.1s/cm and Wcut stoit =3.2s/stoit, following [3]. The number of start and endpoints of the seams are
Ncut stoit , and therefore Ncut stoit = Nseam .
Sewing Cost: The cost of sewing (Csew ) increases proportionally to total seamlength, which is the sum of the circumference of each piece. The cost of sewing
all seam lines is represented as Wsew Lseam , where Wsew is the weight per unit
Lseam . The cost of knotting at seam endpoints also aﬀects sewing time. The costof knotting is represented as Wknot Nknot , where Nknot is the total number ofknots and Wknot is the cost per knot. Nknot equals Nseam (= 2Nseam /2) because

Pillow: Interactive Flattening of a 3D Model for Plush Toy Design5Fig. 5. Seam length and sewing time of a subject

the user knots at the start and endpoints of a seam. Therefore, the cost of sewing(Csew ) is represented as follows:
Csew = Wsew Lseam + Wknot Nknot .
3.2

(4)

Estimation of Weights

We ran an experiment to estimate the two weights Wsew and Wknot . Five users
sewed three lines (5, 10, and 15cm) by reverse-stitching, and we recorded theirsewing times. According to the result, we set Wsew to 22s/cm and Wknot to80s/knot.
3.3

Discussion

The experiment revealed that sewing time diﬀers markedly between individuals.
In addition, it is diﬃcult to estimate the exact sewing time because of several
unpredictable factors such as the physical interference between cloth and string.
However, the study did reveal that for each individual, sewing time was wellapproximated as a linear function of the total seam length (correlation coeﬃcients: 0.8-0.9 (Fig.5)). The prediction result provides valuable information to
avoid excessively complicated seam designs.

4Implementation

Pillow, our prototype system, is implemented as a JavaTM program. Flattening
and reconstruction run in real-time on a standard PC. We use ABF++ as theﬂattening algorithm [4]. It changes a 3D surface segment to a 2D pattern byminimizing the distortion in the angle space. For the physics simulation, wecurrently use a very simple mass-spring model. First, each vertex is moved in anormal direction to mimic outward pressure (Fig. 6(a)). Then, the system adjustsedge length (Fig. 6(b)). We plan to combine our system with more sophisticatedsimulation methods [5] in the future.

6Y. Igarashi and T. Igarashi

(a)

(b)

Fig. 6. Our simple model to mimic the eﬀect of stuﬃng. (a) First, the system moves
each face to its normal direction to simulate the eﬀect of internal pressure; (b) thenthe system adjusts the length of each edge to preserve the integrity of the cloth.

5Results

We created 2D patterns for a teddy bear model using our system and then created real plush toys using the resulting patterns. We used Teddy [6] for creating
the input 3D model, and a standard polygonal mesh representation, so thatusers can use any polygonal model available on the Internet. It is also possible
to create one’s own model using a standard modeling program. Figure 1 shows
an example of a seam design, simulation, and the ﬁnal product. The simulation
successfully captured the overall shape of the real plush toy. We also applied ourmethod to design a balloon (Fig. 7). Figure 2 shows the pattern used to create
this balloon. According to a professional balloon designer, the construction of aFig. 7. A balloon created from the pattern shown in Figure 2Pillow: Interactive Flattening of a 3D Model for Plush Toy Design

7

balloon can be roughly divided into ﬁve steps: creating a 3D model using standard 3D modeling software, manually designing a 2D pattern by cutting andpasting paper sections representing the 3D model (our model was a 1/10 scaleversion of the ﬁnal balloon), scanning the 2D pattern and tracing the contours
using a commercial drawing program, scaling the traced 2D patterns to actual
size and printing it using a plotter, and cutting and sewing the 2D pattern.
The required time from request to delivery is typically 1 month. Using Pillow,
steps 1-3 can be signiﬁcantly shortened (to about 2 weeks), thereby halving total
production time.

6Conclusion and Future WorkWe developed Pillow, an interactive pattern-design system for creating plush
toys and other products. Using the system, users can create 2D patterns easily,and experiment with various segmentations before actually sewing real fabric. In
the future, we plan to improve the ﬂattening algorithm to take cloth properties
into account because existing algorithms (e.g., [7], [4]) for 2D parameterization
do not consider cloth property. We also plan to incorporate more sophisticatedsimulation methods.

References
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Transactions on Graphics (Proceedings of SIGGRAPH 2007) 23(3), Article No.45(2007)
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Computer Graphics Forum (Proc. Eurographics 2004) 24(3), 981–990 (2004)
3. Mitani, J.: Research for a design support system for three-dimensional paper models
using computer. The University of Tokyo Ph.D. dissertation (in Japanese) (2004)
4. Sheﬀer, A., Levy, B., Mogilnitsky, M., Bogomyakov, A.: ABF++: Fast and robust
angle based ﬂattening. ACM Transactions on Graphics 24(2), 311–330 (2005)
5. Grinspun, E., Krysl, P., Schroder, P.: CHARMS: A simple framework for adaptive
simulation. ACM Transactions on Graphics 21(3), 281–290 (2002)
6. Igarashi, T., Matsuoka, S., Tanaka, H.: Teddy: A sketching interface for 3D freeform
design. In: Proc. SIGGRAPH 1999, pp. 409–416 (1999)
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