Envelopment Surface Rendering of Falling Water for ...kenji/Study/File/201106_nicoi.pdf ·...
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Envelopment Surface Rendering of Falling Water for Particle and Volume Based Virtual Liquid Manipulation Model Shunsuke Miyashita 1) , Kenji Funahashi 2) Nagoya Institute of Technology 1) [email protected], 2) [email protected] 1 Introduction This paper describes a method to render en- velopment surface of falling water in an in- teractive manipulation model of virtual liquid that we have proposed for virtual reality sys- tem. In the CG field, although researchers have developed the method to simulate the be- havior of fluid with particle method e.g. SPH method [1], it needs enormous computation time and usually needs parallel processing to realize real-time processing. Therefore, we have already proposed an interactive manipu- lation model of virtual liquid like water which focus on user impression and real-time pro- cessing rather than exact behavior simulation [2]. The model can make user feel realistic sen- sation from the water behavior occurred by user’s manipulation. However, free fall con- dition water is just simulated with particles and rendered as a particle simply. Although metaball and marching cubes method [3] are famous to render surface calculated with par- ticle system, these method are not appropriate for interactive manipulation system because of much calculation time and many times of data scan. In this paper, we propose an ef- ficient and effective rendering method of free fall condition water. To reduce data scanning frequency and searching pattern, it is classified into simple patterns to create process of envel- opment surface from particles in the method. Then envelopment surface is rendered in real- time without parallel processing. 2 Particle and Volume Based Model Our proposed model represents the water as following two conditions to simplify calcula- tion; the stay condition which exists in a con- tainer and the free fall condition which flows from/to container. The stay condition water is treated with the volume value, and the free fall condition one is treated as a simple parti- cle system that particles do not interfere each other. Using this model, total calculation time is reduced drastically, and an interactive water manipulation is realized in real-time. We have improved the stay condition water, that is, we developed the method to express wave, vor- tex and diffusion of color as surface effects of water [4]. The improved model can make user feel more realistic sensation. However, free fall condition water, or each particle is rendered as a simple square polygon, and every polygon is directed to the viewpoint. 3 Envelopment Surface Model The new model renders envelopment surface for free fall condition water that was rendered as a particle simply (Fig. 1). Although each process to make the surface is described and illustrated as two dimension in the following explanation, it is actually rendered in three dimensional space. At first, the 3D space is divided into grid (Fig. 2(a), (b)). Then the following steps are processed every drawing frame. Step 1: Set the grid value where any parti- cle exists to “1” (Fig. 2(c)). The calculation amount of this process is proportional to the number of particles that exist in virtual space. Step 2: Scan and draw each grid as one of the predefined patterns (Fig. 3 ）according to the 8-neighbor of it (Fig. 2(d)). The calculation amount is proportional to the grid size. The grid is often big size, but the number of times the grid is scanned is just one per a frame in our model. z z y x x y Fig. 1: Rendering outline
Transcript of Envelopment Surface Rendering of Falling Water for ...kenji/Study/File/201106_nicoi.pdf ·...
Envelopment Surface Rendering of Falling Waterfor Particle and Volume Based Virtual Liquid
Manipulation ModelShunsuke Miyashita 1), Kenji Funahashi 2)
Nagoya Institute of Technology
1) [email protected], 2) [email protected]
1 Introduction
This paper describes a method to render en-velopment surface of falling water in an in-teractive manipulation model of virtual liquidthat we have proposed for virtual reality sys-tem. In the CG field, although researchershave developed the method to simulate the be-havior of fluid with particle method e.g. SPHmethod [1], it needs enormous computationtime and usually needs parallel processing torealize real-time processing. Therefore, wehave already proposed an interactive manipu-lation model of virtual liquid like water whichfocus on user impression and real-time pro-cessing rather than exact behavior simulation[2]. The model can make user feel realistic sen-sation from the water behavior occurred byuser’s manipulation. However, free fall con-dition water is just simulated with particlesand rendered as a particle simply. Althoughmetaball and marching cubes method [3] arefamous to render surface calculated with par-ticle system, these method are not appropriatefor interactive manipulation system becauseof much calculation time and many times ofdata scan. In this paper, we propose an ef-ficient and effective rendering method of freefall condition water. To reduce data scanningfrequency and searching pattern, it is classifiedinto simple patterns to create process of envel-opment surface from particles in the method.Then envelopment surface is rendered in real-time without parallel processing.
2 Particle and Volume Based Model
Our proposed model represents the water asfollowing two conditions to simplify calcula-tion; the stay condition which exists in a con-tainer and the free fall condition which flowsfrom/to container. The stay condition wateris treated with the volume value, and the freefall condition one is treated as a simple parti-cle system that particles do not interfere eachother. Using this model, total calculation timeis reduced drastically, and an interactive watermanipulation is realized in real-time. We have
improved the stay condition water, that is, wedeveloped the method to express wave, vor-tex and diffusion of color as surface effects ofwater [4]. The improved model can make userfeel more realistic sensation. However, free fallcondition water, or each particle is rendered asa simple square polygon, and every polygon isdirected to the viewpoint.
3 Envelopment Surface Model
The new model renders envelopment surfacefor free fall condition water that was renderedas a particle simply (Fig. 1). Although eachprocess to make the surface is described andillustrated as two dimension in the followingexplanation, it is actually rendered in threedimensional space. At first, the 3D space isdivided into grid (Fig. 2(a), (b)). Then thefollowing steps are processed every drawingframe.Step 1: Set the grid value where any parti-cle exists to “1” (Fig. 2(c)). The calculationamount of this process is proportional to thenumber of particles that exist in virtual space.Step 2: Scan and draw each grid as one of thepredefined patterns (Fig. 3）according to the8-neighbor of it (Fig. 2(d)). The calculationamount is proportional to the grid size.The grid is often big size, but the number oftimes the grid is scanned is just one per aframe in our model.
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Fig. 3: Examples of 12 predefined parentpatterns, each pattern has 0–7 childpatterns in 2D
4 Experiment
Using the model mentioned above, we im-plemented a virtual liquid manipulation sys-tem (Fig. 4). User can move a container withPOLHEMUS 3SPACE ISOTRAK II. We com-pared this new model that renders envelop-ment surface (Fig. 5(left)) with previous modelthat renders particles directly (Fig. 5(right)).The envelopment surface is rendered and cov-ers particles which decide the behavior of freefall liquid, so user feel more realistic sensationat depth and spatial effect. The processingspeed is 29 fps with about 1500 number of par-ticles where the grid size is 120 × 120 × 60.It means interactive manipulation is realizedin real-time.
5 Conclusion
In this paper, we proposed an efficient andeffective rendering model of free fall water withenvelopment surface. It can make more real-
Fig. 4: Appearance of experimental system
Fig. 5: Envelopment surface and particles
istic sensation. As a future work, we shouldimprove visual effects of envelopment surface,e.g. at shading process, and rendering speednot only for experimental system but for ap-plication system. We are now promoting toapply this virtual water manipulation modelto new e-learning system based on VR tech-nique e.g. virtual experience system of chem-ical laboratory. Realistic sensation felt fromthe liquid manipulation and real-time process-ing on low-priced PC are important than theexact behavior of water for the system like de-scribed above.
References[1] F. Losasso, J.O Talton, N. Kwatra and R.
Fedkiw, “Two-Way Coupled SPH and Parti-cle Level Set Fluid Simulation”, IEEE Transac-tions on Visualization and Computer Graphics,Vol.14, No.4, pp.797–804, 2008.
[2] Kenji Funahashi, Yuji Iwahori, “Manipulationof Liquid Using Cases in Virtual Space”, Proc.IEEE ROMAN2000, pp.368–373, 2000.
[3] W.E. Lorensen and H.E. Cline, “Marchingcubes: A high resolution 3D surface construc-tion algorithm”, ACM SIGGRAPH ComputerGraphics, Vol.21, No.4, pp.163–169, 1987.
[4] Yuki Natsume, Andreas Lindroos, HirotakaItoh, Kenji Funahashi，“The Virtual Chem-ical Laboratory Using Particle and VolumeBased Liquid Model”, Proc. SCIS & ISIS 2010,pp.1354–1359, 2010.
