Method for Creating Nighttime Textures that Considers the Uses of Buildings

Transcription

1 Method for Creating Nighttime Textures that Considers the Uses of Buildings Toru Isohata Kouki Itoh Tsukasa Kikuchi Takushoku University graduate school, Takushoku University k-itoh, Abstract Nightscapes are defined here as scenery based on artificial light sources in nighttime cityscapes. This paper proposes a method for effectively expressing light flooding out of buildings as the main light source for creating nightscapes. In the proposed method, nightscape textures are created by considering the way that lighting in office or residential buildings, the color of illumination, differences in types, and so on. Then, the textures that were created for the buildings in a cityscape model are automatically mapped to express the nightscape. In other words, a nightscape texture database is created by considering differences in building uses to conduct mapping in the building model. Furthermore, by applying building uses in combination with temporal changes in window brightness, it is possible to create animated nighttime scenes that change over time. Textures for use in mapping in building models for nighttime scenes are selected by considering whether the building is an office, residential, or other type of building, the areal ratio of each side of the building model, the elements that face the various sides of the building, and the compass direction. With the proposed method, it is not necessary to do rendering and allocate many light sources to reproduce nighttime scenes. Instead, it is possible to create animations not only from static images, but also in conjunction with temporal changes without incurring calculation costs. Keywords: Nightscape, Cityscape, Building use, Texture mapping 1. Introduction Rendering (Photo realistic Rendering) realistic technique in Computer Graphics (CG) has been proposed various the one so far, built into an application on the market, and supplied to practical use. A still limited calculation cost is needed even so though the speed-up algorithm is proposed as for the realistic photo rendering because there are a lot of one of the approach of calculating the behavior of light in optics. Therefore, the number of light sources included in the scene that tries to be made has not exceeded it to few. When the outdoor scenery is reproduced with CG, the nightscape is enumerated in one of the scenery where a lot of light sources are needed. Nightscape is not a natural light sources of moonlight etc. but the scenery by source of artificial light is indicated. Especially, the scenery that seems to be overcrowded of light, a searchlight, and an advertising lighting, etc. that leak from the building and go out in view is indicated, and there are a lot of nightscape. In this paper, it pays attention to " light flooding out of buildings " that is the main light source in the cityscape of the night. And it is build to database of texture for nightscape that considers building uses. And it proposes the generation method of an efficient nightscape by the texture mapping to building model. The calculation cost becomes huge in having faithfully arranged the light source in these when there are a lot of numbers and kinds (signboard etc. of the lamp of the light in the window and the car, streetlights, and illumination) of the light source, and it reproduces it with CG in the cityscape where the population and the density of the building are high. Then, the building model of the unit that gives the writing is generated and the large-scale city nightscape that suppresses the calculation cost is generated with the prior assumption of the rendering doing and it and a texture doing the mapping to the building model in the cityscape in this paper (Fig.1). The animation of the nightscape with a time change is enabled to be generated in addition by constructing the data base of the texture that considers the time change. Fig.1 Result image by technique for proposing it with this paper When the texture of the building is made, it is necessary to decide

2 ON/OFF of the window light of the building. When the window of the building is caught as a lattice arrangement of two dimensions, the algorithm that decides ON/OFF of the window light includes Conway's Game of Life [1]. It is a simulation where a simple model reproduces the processes of the birth of the life, evolution, and the selection, etc., and life and death is expressed by ON/OFF of the cell arranged on the lattice two dimensions. Each cell includes the cell near eight that is called Moore neighborhood, and the state of the next step of a certain cell (generation) is decided by the state in a generation in the Moore neighborhood today. The uses of the building, the direction of the building wall, and it is necessary to consider the distance with the adjacent building etc., and Conway's Game of Life cannot be applied to the ON/OFF judgment of the window light of the building in this paper as it is. L-System[2] by Prusinkiewicz, P. is one of the typical algorithm that describes the structure of the natural product like the growth process etc. of the plant based on the reflexive. The time series variation that can be applied to the reproduction of the time change of the nightscape is not considered though the reflexive can be applied to the ON/OFF judgment of the light. Building automatic modeling of the procedural by Pascal Mueller is enumerated for the modeling of the cityscape in CG [3]. ON/OFF of the window light of an architectural model is not considered the techniques of Pascal Mueller are to generate an architectural model with the automatic operation by applying L-System, and the generation of the nightscape is not possible. Moreover, because the effort and the calculation cost of the creator are needed when the space is composed, it is not possible to apply it to the generation of the texture that does the mapping to the building model in this paper. Moreover, the element not to be able to lack because of the generation of the nightscape includes the rendering method by the global lighting model [4]. A global lighting is an image synthesis method that simulates all scattering light in the model based on laws of physics. To calculate indirect light, the cost of some computing time and the memory consumption is not avoided though high-speed photon mapping method that uses hierarchical grid structure (Radiance Grid Pyramid) by Youg-Hao Yue [5] is enumerated in an effective technique for decreasing the computing time of a global lighting. The texture for the nightscape is generated in consideration of how of the light in the window to light up, the color of the lighting in the building for the office building and the dwelling, and unlike the kind of, it proposes the texture generated to the building in the cityscape model, and it proposes the technique for reproducing the nightscape by automatically doing the mapping in such and this paper. That is, the database of the texture for the nightscape is constructed in consideration of the building uses, and the building model is done the mapping. Moreover, the generation of the animation of the nightscape with a time change is enabled by combining the building uses with the temporal variation of the light in the window. Nightscape for texture building model mapping do the building office for building dwelling for building additionally building model side area ratio direction in consideration of texture select. It becomes possible not only the still picture of the nightscape but also to generate animation with a time change without need not being necessary to do rendering by arranging a lot of light source to reproduce the scene of the nightscape by the proper move method, and putting the calculation cost. In this paper is composed as follows. Chapter 2 describes the outline of the building model by whom the texture for the nightscape proposes with this paper is done in the mapping. Chapter 3 describes the outline of the texture for the nightscape, and Chapter 4 describes the generation method of the texture of the building for the characteristic element and the nightscape. Chapter 5 describes the texture mapping of the building model. Chapter 6 describes the example of simulating the visual of the nightscape that uses the texture for the nightscape. Finally, the summary and the problem in the future of this paper are referred in Chapter Urban model and outline of building model This chapter describes the generation method of the building model by whom the texture for the nightscape proposes with this paper is done in the mapping. It uses as the of procedural design rule is recurrent, and a detailed building is made from the geometrical model who combines it (Fig.2). In addition, L-System is applied in building automatic modeling of the procedural by Pascal Mueller [3] for the generation method of a large-scale cityscape and the building model. Various large-scale city model is generated with a little calculation cost (Fig.3). Concretely, the set grammar proposed by Wonka and L-systems are applied CGA (Computer Graphics Architecture) Shape method, and the building model is generated with the repetition division algorithm. The range of the building model is set on the premises, basic geometrical models are combined, and the large-scale city model is composed as shown in Fig.2. In this paper, the technique by Pascal Mueller is applied, and the building model and the large-scale cityscape model are generated. In that case, the building model is assumed to be the one generated with the polygon, and each wall of the building model and the polygon that composes it are memorized to be possible to distinguish. That is, to number and to distinguish the polygon that composes the wall in addition in each wall where the building model is composed for one model of the building, the flag is set up and memorized. As a result, it only has to calculate the total of the area of each polygon that composes the wall when automatic texture mapping to the building wall is enabled, and the area of each wall of the building model is calculated in addition, and it becomes easy to calculate the ratio of the area of the wall.

3 Fig.2 Combined mass model Fig.4 Characteristic element of building and hierarchy of priority level Fig.3 The large-scale city model's generation 3. Outline of texture for nightscape This chapter describes the outline of the texture for the nightscape proposes with this paper. In this paper, it pays attention to "light flooding out of buildings" that is the main light source in the cityscape of the night, and the data base of the texture for the nightscape that considers the building uses is constructed. When the data base of the texture for the nightscape is constructed, the texture is generated in consideration of the time zone that the area ratio of the characteristic of the building, that is, the building uses and the direction and each wall for which the building wall is suitable and generated the nightscape scenes assume. The characteristic element of the building in the texture generation that should be considered and the hierarchy (priority level of the texture selection) in the data base are as shown in Fig.4. When the building model is done the texture in the mapping, it decides from a high-ranking element of the hierarchy by which the characteristic of the building in the mapping is shown in Fig.4, and the texture that does the mapping is derived from the data base. They are made to correspond to the floor space of the building model based on Chapter 2 Article 28 the Construction Standard Act [7] (It is described clearly in this paper as follows as construction Article 28) and the number and the size of the window in the building model in this paper are set. Room (Limit it to the room for the residence, the classroom at the school, and the one decided by the government ordinance to belong to these,sickroom. Additionally of the hospital), window for the lighting though provided in these by the government ordinance additionally in the belonging building. The house, the school, the hospital, the clinic, the dormitory, and the lodging house, it is necessary to install other opening, and up to 1/7 or more between from 1/5 to the tenth in the house to the floor space of the room more than the ratio provided by the government ordinance the area of an effective part for the lighting in other buildings. That is, the number of windows of the one floor is assumed to be 9 pieces in the proper move method, and it divides into three blocks of three pieces in the office building. Because the floor space of an average building in Japan is assumed to be 80 tsubo in this paper. The number of windows of the one floor was assumed to be 9 pieces so that the size of the window may generate the texture in the window in the office building whose 1/7 or less of the floor spaces is other buildings in the building for the dwelling based on the relation between the floor space of construction Article 28 and the size of the window so as not to become small more between from 1/5 to 1/10. In addition, the purpose of dividing the number of windows of the office building into the block of 3 pieces is to enable texture mapping with an elevator, an escape stairway often located at the ON/OFF control and the center of the block unit of the building wall by assuming the number of windows to be 3 pieces to enable the change of the color of the light locally in addition to ON/OFF of the window

4 light, and connecting the three blocks of three pieces, and a different kind of light. The kind of a necessary texture is assumed to be "Window", "Escape stairway", "Elevator", and "Door" by the data base making. The characteristic element of the building shown in Fig.4 and the generation method of the texture are described in Chapter 4. The link structure of Fig.4 describes only the main line clearly in consideration of the easiness of figure to see. 4. Characteristic element of building and generation method of texture This chapter describes the generation method of the texture for the characteristic element of the building and the nightscape that reflects it. 4.1 Texture generation for nightscape that considers uses of building The building uses in this paper indicates how of the light in the window in the building for the office building and the dwelling to light up and the color of the lighting and the kind of difference. It is an office building or the texture for the nightscape that considers whether it is a building for the dwelling is generated with various variations, it links as a layered structure according to the priority level shown in Fig.4, and the data base is constructed. And, the texture for the nightscape of the data base is generated and the scene of the nightscape is generated with doing the mapping to the building model automatically. The generation method of a concrete texture is as follows. When ON/OFF of the light is decided, the texture is generated by doing the building model of the unit that gives the writing only to the window of turning on (one floor) in rendering. Prepare several kinds of lights set up in that case. Even if it is a same building uses, the window that includes the window shade and the curtain, etc. becomes possible to enrich the variation of the texture by preparing several kinds of lights even if it is the same color window because the degree of light that overflows and goes out weakens, too it. The light decided at the start of the simulation assumes the one that the same kind is selected, and applies the simulation after time passes only to the window of turning on though is assumed to select the selection of the light at random from among the prepared light. When the cityscape of the night is reproduced, it is necessary to express how of the light in the window to light up, the color of the lighting, and the kind of difference in consideration of the building uses. Because behavior of light in window is different in building for office building and dwelling Characteristic of office building and generation method of texture It is often controlled for the office building in every not the ON/OFF of one in the window light control but the entire one floor or the block in the one floor (Fig.5). When one in the window one is made a cell, it is necessary to control ON/OFF of the cell as sets of the number that is. It has often lit it since daytime, and moreover, it is characterized also that a lot of lights have already lit up at time to begin to see the light as a nightscape and is enumerated the office. The office building is turned off because everyone ends and is gone to the floor or the block. That is, the probability that the light continues as turning off until the start of work time of the next day is very high when turning it off once. There are a lot of white fluorescent lamps of the kind and the color of the light. Fig.5 Photograph in office building In this paper, the texture for the office building is generated according to the following procedures. (1) The number of window cells on the one floor is assumed 9 pieces, and divided into the three blocks of three pieces as described in Chapter 3. (2) ON/OFF of three blocks function value Y' is decided by the comparison about probability value Y in which 1/f β noise is added to the function shown in expression (1). Y ' = e Y = Y ' + a( t) = bt + c t 2 f 1 β ( 0 t) + a( t) (1)

5 Here, b and c are the arbitrary constants in t at the simulation time. Refer to document [8] for details for 1/f β noise. When expression (1) is shown in the graph, it becomes as shown in Fig.6. When probability value Y is smaller than function value Y' When it is larger, the light of the block is assumed turning on, and probability value Y is function value Y', the light of the block is assumed turning off from expression (1). However, probability value Y function value Y' sets the constant from the simulation start time to the midnight of the nightscape as shown in Fig.6 like being strong the tendency to grow more. (3) The time change concerning how of the light to light up is as for step (2). It expresses it by repeating it. However, never turn on the block that became one degree turning off for the texture of the office building. Therefore, the simulation comes to continue only to the block that is turning on. In addition, there is a possibility of becoming turning on afterwards even when becoming it turning off the light in the window by going to bed because life is led in the building for the dwelling after it closing time. As for the kind and the color of the light, a lot of lamp color in addition to white fluorescent lamp orange etc. are seen. Fig.6 Graph chart of expression (1) Therefore, a necessary texture is as follows in the office building (Fig.7). Fig.7 Texture of office building Characteristic of building for dwelling and generation method of texture It is possible for the building for the dwelling and the office building to differ, to control the light in each cell in the floor or the window it is not every a block (Fig.8). And to have lit it in consideration of commuting and power saving since daytime that time when the light is inevitably turned on from the office building slows because it is few, too. Fig.8 Photograph in dwelling building (1) In this paper, the texture for the building for the dwelling is generated according to the following procedures. (2) ON/OFF of the window cell function value Y' is decided by the comparison about probability value Y in which 1/f β noise is added to the function shown in expression (2). Y Y ' ' = mt = e t Y = Y ' + 2 f 2 1 β + n ( 0 t < L) ( L t) (2) Here, it is simulation time, and L is threshold time (arbitrariness) in m and n in t to switch the function value as for the arbitrary constant. Refer to document 8 for details for 1/f β noise. When expression (2) is shown in the graph, it becomes as shown in Fig.9. When probability value Y is smaller than function value Y' When it is larger, the window cell is assumed turning on, and probability

6 value Y is function value Y', the window cell is assumed turning off from expression (2). (3) The time change concerning how of the light to light up is expressed by repeating step (2). an internal appearance. Therefore, the mapping of the texture that arranges the window cell is done. The side where the area is small must not do the mapping to the texture of the window cell considering the elevator and the escape stairway. Fig.9 Graph chart of expression (2) Therefore, a necessary texture is as follows in the dwelling building (Fig.10). Fig.10 Texture of dwelling building 4.2 Direction and area ratio of building model wall As for the building, the number, shape, and the size of the window might be different according to the direction. A different point is a little because there are a lot of buildings of comparatively as the rectangle simple shape the office building. Each element of the window by the direction on the other hand, the building for the dwelling includes buildings of shape other than the rectangle, and the component such as windows and doors is different in each direction. Moreover, it is also remarkable that there are often a lot of windows in the south in consideration of sunshine. Then, texture mapping that considers the direction is enabled by generating the texture of the building of each north, south, east, and west. The window is arranged on the south, the east, and the west side, and not arranging the window so much becomes possible by considering the direction on the north side in the building for the dwelling in the apartment house etc. Moreover, the selection of the texture changes depending on the area ratio of the building model each wall. There are a lot of numbers of windows because the side where the area is large sees a lighting and 5. Texture mapping of building model This chapter describes the mapping of the texture for the nightscape to the building model. When the building model is done the texture for the nightscape in the mapping, the basis of selection of the number and the size of the window that enters the one floor is as follows. 1. The wall where the area is the largest is calculated. It follows the gross area and the construction Article 28 of the polygon, and the number and the size of the window that enters the one floor are decided. 2. It corresponds to the mapping to a small building by decreasing the number of windows that reduce the size of the window small of the floor space and enter the one floor by applying providing the size of the window to the floor space of the room by construction Article 28 based on the wall where the area is the largest for the window of a small building. Concretely, the outside frame of the texture for the nightscape is prepared and a binary image of which it is white the black, and the window is prepared. The texture is cut in the place in which it installs on the width of the building so that the window may tune off when it reduces so as not to become small more than the size of the window that white provides by construction Article 28, and the window is displayed to the building model. And, the fitting does the size of the texture according to the area of the building. A binary image is prepared because of the texture and the pair for one nightscape. The texture for the nightscape is done in the building model after the number and the size of the window that enters the one floor are decided and the mapping is done as stated above by doing the tiling in each one floor. The tiling is a technique when the building model is done the texture in the mapping. In one respect, the expression that repeats the same pattern continuously becomes possible by doing the mapping not one piece of the texture in respect of the building model but two or more pieces of the tile. This paper tiling do kind building uses suitable data base several kinds of nightscape for texture one floor mapping do window light turn on turn off express. In addition building two or more color light assume usually tiling contingency in consideration of differ kind of data base texture key point mapping do window light same become have become. The tiling is done from the undermost layer of the building model who is the smallest coordinates on as a procedure of texture mapping in each one floor (Fig.11).

7 Fig.11 Example of tiling 6. Example of simulating visual of nightscape The result of simulating the visual of the nightscape is shown in Fig.12 by paying attention to the light flooding out of buildings from the generation method of the texture for the nightscape proposes with this paper, that is, the building and occurs, and using the texture for the nightscape generated in consideration of the building uses. 6.1 Simulation environment The environment used for the simulation is as follows. Use computer:hp Z400 Workstation CPU:Intel Xeon 3.19GHz Memory:8GB Use OS:Windows7(64bit) Graphics card:nvidia Quadro FX 1800 Number of building models:361 Parameter numerical value:(1) β=1.5,b=10,c=90, (2) β=1.5,m=20,n=25,l=21 This simulation is mounted as a plug-in using MaxScript of Autodesk 3ds Max 2009, and V-Ray is used for rendering. Fig.12 Example of simulating nightscape that uses texture for nightscape 6.2 Consideration concerning simulation result In the simulation, the scene of the nightscape that considered the building uses was able to be generated to the large-scale city model presented in precedence study [3] by doing the texture for the nightscape by the technique for proposing it with this paper in the mapping. As for the technique for expressing the window light by the mapping to the building model, it has been understood that the time required for the simulation can be decreased, and this simulation procedure is effective from the simulation result in Fig.12. Moreover, the building's for the office building and the dwelling existing together on average in the scene for the animation of the nightscape scene by having combined the time changes is not seen so much in the real world, and can simulate such a scene arbitrarily. However, it is thought that it is necessary to consider light source other than the window light and indirect light by it in reproducing the cityscape of the night. Especially, the streetlight is very important as indirect light to the building. Because the streetlight is a role to shine on surroundings and exists, strength of the light cannot be disregarded. Moreover, it is future tasks to express the interference with the light source of the building model who is mutually adjacent by whom texture mapping is done etc.

8 7. Summary and problem in the future In this paper, it paid attention to "light flooding out of buildings" that was the main light source in the cityscape of the night, and it proposed the generation method of an efficient nightscape to the database architecture of the texture for the nightscape that considered the building uses and the building model by the mapping. It became possible to generate the large-scale city nightscape that suppressed the calculation cost because it did the mapping to the building model in the cityscape beforehand as the rendering doing and its texture the building model of the unit that had given the writing. In addition, the animation of the nightscape with a time change was able to be generated by constructing the data base of the texture that considered the time change. The element of the building uses includes the data base making of the texture that generates the building for the commerce not taken up the texture, and considers LOD etc. in this paper the production of the texture that considers indirect light such as the skies to the wall by the height of time zone and the building and streetlights future tasks. References [1] John Horton Conway, Conway's Game of Life, [2] Prusinkiewicz, P., and Lindenmayer, A., The Algorithmic Beauty of Plants, Springer Verlag. [3] Pascal Mueller, Peter Wonka, Simon Haegler, Andreas Ulmer, Luc Van Gool, Procedural Modeling of Buildings, Proceedings of ACM SIGGRAPH 2006 / ACM Transactions on Graphics. [4] Henrik Wann Jensen, Takeshi Naemura (translation), Realistic Image Synthesis Using Photon Mapping, Ohmsha Corporation, 2002, ISBN [5] Yong-Hao Yue, Kei Iwasaki and Tomoyuki Nishita : Radiance Grid Pyramid : A Fast Photon Mapping Suited for Final Gathering, Corporate juridical person, Information Processing Society of Japan Technical Report, [6] Wonka, P.,Wimmer, M.,Sillion,F.,And Ribarsky, W Instant architecture. ACM Transactions on Graphics 22, 3, [7] Chapter 2 Article 28 the Construction Standard Act, [8] Mamat, A., Fujimoto, T., Mamtimin, G., And Chiba, N., An Efficient Hybrid Method for Animating the Growth of Large-Scale Cumulus-Type Cloud., The Journal of the Society for Art and Science, Vol.6, No.4, , 2007.