Interactive Manipulation Model of Group of
Individual Bodies for VR Cooking System
Atsushi Morii, Daisuke Yamamoto, and Kenji Funahashi
Nagoya Institute of Technology,
Cokiso-cho, Showa-ku, Nagoya, 466-8555, Japan
morii@center.nitech.ac.jp
yamamoto.daisuke@nitech.ac.jp
kenji@nitech.ac.jp
http://www.center.nitech.ac.jp/

Abstract. A new high-speed manipulation model for a group of individual bodies (GIB) such as sand and lava is proposed in this paper.
One of the goals of this research is to use it for applications such ashome VR cooking systems for representing eg. a mass of fried rice. In
this model, GIB is represented as a height ﬁeld. Variation in the heightﬁeld represents movement of the GIB. Transformation of GIB in wide
spaces which is beyond adjacent grids is considered. GIB is treated as oneobject, which means that calculation is done eﬃciently on one object.
Transformation of GIB is calculated quickly. Interactivity has a priority
over correct movement of GIB in this model.
Keywords: a group of individual bodies, VR cooking system, home use

1Introduction

In recent years, research about interactive manipulation for sand and lava has
been performed [1] [2]. In these researches, transformation of a group of individual bodies (GIB) such as lava and sand in a wide spaces which is beyond
adjacent grids needs multiple calculations over a timeframe. For example, in asand manipulation model [2], the collapse of the GIB is calculated by searching
adjacent grids on every timeframe. The transformation of the GIB surface isconducted by sequences of calculations. In this paper, we propose a high-speed
GIB model which only needs a few calculations for a certain point of time. Inthis model, we consider transformation of GIB in wide spaces which is beyond
adjacent grids. GIB is treated as one object, which is calculated quickly.

2

Manipulation Model of GIB

Transformation Surface. In this model, GIB is deﬁned as a height ﬁeld which
is ﬁxed on a container. Transformation of the GIB is calculated from a curved
surface. When the GIB exists in the center of a container, for example (Fig.11), transformation surface (TS) is generated around place where the GIB seem2

Manipulation of a Group of Individual Bodies

to slide down to (Fig.1-2 the black part), and the volume is added to the GIB(Fig.1-3). Then the GIB volume is corrected (Fig.1-4), and as a result the GIB ismoved. A TS is generated as a half of elliptic cylinder for simpliﬁed calculation[3]. For example, when the container is tilted, a TS is generated in Fig.2. Whenan acceleration is applied to the container, the GIB receives a reaction force.
The TS is calculated from the gravity and the reaction force.

Fig. 1. Vertical section of GIB and container

Fig. 2. TS of a half of elliptic cylinder

Fig. 3. Process of GIB movement

Expression Based on Existence Probability. Though TS model is quick
because of its simple method, this model is insuﬃcient in expressing the GIB’smovement. To represent the process of GIB movement, we conduct an expression
based on existence probability. When TS is generated on the place where TS isisolated from GIB in Fig.3 (left), we suppose that GIB are sliding down on thecontainer. In this case, the GIB spreads both at the top of container and TS.
Each grid of height ﬁeld in the container are added random values based on
existence probability (Fig.3 right). This expression is continued as long as morethan a threshold volume exists between the center and the top of the container.
Particle System. We also implement a particle system [4] in this model. In
order to implement the system, we locate the particles in height ﬁeld values.
Particle collision is detected on the surface of the height ﬁeld. They also fall
down when the container is tilted, and then the total volume of the GIB in thecontainer is decreased. Only a few particles are used for maintaining a level ofrealism.

Manipulation of a Group of Individual Bodies

33Experiment and Conclusion

The experiment was constructed on a system with a WiiRemote using a Intel
Pentium Dual Core E5200 2.5GHz CPU, 1024MB RAM. In this system, the GIB
is supposed as fried rice (not traditional Chinese fried rice but Japanese) and thecontainer as a skillet (Fig.4). Through this system, subjects were able to movefried rice by moving the container. 8 subjects evaluated the GIB movement’s
realism by classifying the score into seven grades. 1st grade is “This model
doesn’t feel real enough for a cooking system”. 7th grade is “It is as natural as areal one”. 3 subjects evaluated it as 4. 4 subjects evaluated it as 5. One subject
evaluated it as 6. The results of the performance test is shown in the Table 1.
We got some positive evaluations such as that GIB movement seems natural
with 331 vertices and 670 particles. Good results were obtained but there aresome points that need improvement. We have to improve upward movement of
the GIB without the particle system. We are also developing a model for using
cooking tools e.g. a spatula in this model.

Fig. 4. System appearance

References
1. Stora, D., Agliati, P. O., Cani, M. P., Neyret, F., andGascuel, J. D.: Animating lava ﬂows. In: Proc. of theGraphics Interface, pp.203–210 (1999)
2. Onoue, K., and Nishita, T.: Virtual Sandbox. In:
Proc. of the 11th Paciﬁc Graphics, pp.252–259 (2003)
3. Morii, A., Yamamoto, D., and Funahashi, K.: Gridand particle based model of group of individual bodies
for VR cooking system. In: Proc. of the 14th VirtualReality Society of Japan Annual Conference (DVD,in Japanese) (2009)
4. Harada, T., Tanaka, M., Koshizuka, S., andKawaguchi, Y.: Real-time Coupling of Fluids andRigid Bodies. In: Proc. of the APCOM’07-EPMESC
XI (2007)

Table 1. Performance results(sorry; this table is correctedfrom the proceedings)
Vertices Particles FPS
331

630

68

631

1210

33

817

1560

22