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GIS Data for Atmosphere Environmental Simulation
TSINGHUA SCIENCE AND TECHNOLOGY ISSN 1007-0214 66/67 pp412-417 Volume 13, Number S1, October 2008
Development of an Accurate Urban Modeling System Using CAD/GIS Data for Atmosphere Environmental Simulation Tomosato Takada, Kazuo Kashiyama** Department of Civil Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan Abstract: This paper presents an urban modeling system using CAD/GIS data for atmosphere environmental simulation, such as wind flow and contaminant spread in urban area. The CAD data is used for the shape modeling for the high-storied buildings and civil structures with complicated shape since the data for that is not included in the 3D-GIS data accurately. The unstructured mesh based on the tetrahedron element is employed in order to express the urban structures with complicated shape accurately. It is difficult to understand the quality of shape model and mesh by the conventional visualization technique. In this paper, the stereoscopic visualization using virtual reality (VR) technology is employed for the verification of the quality of shape model and mesh. The present system is applied to the atmosphere environmental simulation in urban area and is shown to be an useful planning and design tool to investigate the atmosphere environmental problem. Key words: CAD/GIS; urban modeling; mesh generation; atmosphere environmental simulation; stereoscopic visualization; virtual reality
Introduction Recently, the atmosphere environment in urban area, such as strong wind flows around high-storied buildings, air pollution and heat island, is becoming serious problems. In order to investigate those problems, it is important to develop the method to evaluate the atmosphere environment accurately. The numerical simulation is a becoming powerful tool to evaluate that in accordance with the development of computer hardware and simulation technology. In the practical computation of this simulation, it is very important to prepare the accurate shape model and good finite element mesh in order to obtain the accurate numerical results. The finite element method is a suitable method for this type of simulation, since the finite element Received: 2008-05-28
** To whom correspondence should be addressed. E-mail: [email protected]
method can deal with the arbitrary shape of structures. This paper presents an urban modeling system using CAD/GIS data for atmosphere environmental simulation. Several CAD/GIS data are used for the preparation of shape modeling and an automatic mesh generation method based on the tetrahedron element in order to express the urban structures with complicated shape accurately. It is difficult to evaluate the quality of the mesh generated for the complicated computational domain by the ordinal visualization technique. In this paper, the stereoscopic visualization using virtual reality (VR) technology[1] is employed for the evaluation of that for urban structures with complicated shape in order to solve this problem. The immersive projection technology (IPT)[2] is employed for VR technology and the active stereo method is employed for stereoscopic view. The present system is applied to the atmosphere environmental simulation around Nihonbashi, Tokyo, and is shown to be a useful and powerful tool to investigate
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
413
the atmosphere environmental problem.
1 Modeling for Urban Area Figure 1 shows the flow chart of the modeling system for urban area. Modeling for landform Modeling for structures
Fig. 2 Grid surface and building polygon
Conversion to DXF file Combination of each model Fix the computational domain Surface mesh generation Visualization of surface mesh using virtual reality technology Verification of mesh quality 3-dimensional Delaunay method Solid mesh generation Fig. 1
1.1
Flow chart for modeling for urban area
Surface mesh generation for urban area
1.1.1 Modeling for landform For the modeling for the landform, two kinds of GIS data, the digital elevation maps (DEM) issued by Japanese geographical survey institute and 2D house maps (MAPPLE2500) are employed. For the DEM, grid interval is 5 m. Using the data of DEM, a more fine grid which is called as grid surface is created and the elevation at node is interpolated by the cubic spline interpolation method. Figure 2 shows the elevation and the polygon for the buildings obtained from 2D GIS data for buildings. Nodal points are generated on the boundary of building polygon at 2 m intervals and the nodal elevation is given by the interpolation using the nodal elevation data of the grid surface. Using the nodes on the ground surface, the ground surface mesh based on the triangular element is generated by the modified Delaunay triangular method[3]. Figure 3 shows the surface mesh on the ground for urban area.
Fig. 3
Mesh on the ground for urban area
1.1.2 Modeling for structures The urban structures are classified into two types: the simple shape model and complicated shape model. The different modeling methods are employed in this system. (a) Modeling for structures with simple shape The three dimensional shape for structures with simple shape is created by the extension of 2D horizontal shape to the vertical direction (see Fig. 4). The Building height is determined by the data of story of building. The height of one story is assumed to be 4m. The surface mesh is created to the side and top of the building. The structured triangular mesh is prepared for the side wall by the algebraic grid generation method based on Lagrange interpolation. For the top surface, the unstructured triangular mesh is created by the A structure with simple shape
Top part
Classification into two parts Mesh generation 2D boudaryof the building Side part Fig.4 Concept of the mesh generationmethod for structures with simple shape
Tsinghua Science and Technology, October 2008, 13(S1): 412-417
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Delaunay triangular method because the shape of top is arbitrary in most cases. The shape modeling and mesh generation for the structures with simple are performed automatically by using the structure ID number, which is a unique number to discriminate each structure. (b) Modeling for structures with complicated shape For the mesh generation for urban structures with complicated shape, at first, the shape model is created using the CAD system accurately. Next, the surface mesh is generated by the Delaunay method (for top roof) and Lagrange interpolation method (for side wall). Figure 5 shows the surface mesh around the bridge and expressway and Fig. 6 shows the buildings with complicated shape.
structure model. Figure 8 shows the shape model of urban area without the expressway. In Figs. 7 and 8, the color structures indicate the shape model created by the CAD system. The red part denotes the expressway and the blue part shows the river. Figures 7 and 8 show the difference of landscape view by presence of the expressway. From these figures, the finite element model created by this method can be applied not only for numerical simulation but also for landscape simulation. Figures 9 and 10 show the landscape view. The purpose of numerical simulation is to understand the effect of the expressway to wind flow field.
Fig. 7
Fig. 5
Shape model of urban area
Surface mesh around the bridge and expressway
Fig. 8 Shape model of urban area not including the expressway
Fig. 6
Surface mesh around the building Fig. 9 Landscape view with the expressway
1.1.3 Data conversion to DXF file and combination of each model The data format of surface mesh for ground and building is converted to the drawing interchange file (DXF) data format. This conversion enables to combine the both mesh data by using the CAD system. Figure 7 shows the shape model of urban area after combination of the ground surface model and urban
Fig. 10 Landscape view without the expressway
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
415
1.2 3D computational domain In order to simulate for the atmosphere environment in urban area, the computational domain is fixed. Figure 11 shows the computational domain as numerical wind tunnel. In Fig. 11, the circle domain can rotate and it is possible to change the inflow wind direction same as experimental wind tunnel. The shear slip method is employed at the connecting domain to turntable. Figure 12 shows the mesh around the connecting domain. Figures 13 and 14 show exterior and interior view of computational domain. It can be seen that the fine mesh is employed near the turn table. 2 km
1 km
4 km
Fig. 11 Numerical wind tunnel
Fig. 14 Interior of computational domain
1.3
The mesh generation in interior domain is performed using the surface mesh data. The unstructured tetrahedral mesh is generated for the 3D domain by the Delaunay method.
2
Mesh around the connecting domain
Fig. 13 Exterior of computational domain
Virtual Reality System
Virtual reality (VR) is an important technology for the visualization in computer simulation. The quality of VR image is improved rapidly in accordance with the development of VR technology. Observers can see objects or physical phenomena 3-dimensionally by the stereoscopic view created by VR device. 2.1
Fig. 12
Finite element discretization in 3D domain
VR projector and display system
Immersive projection technology (IPT) is employed for VR technology and the immersive display is employed for VR display. Figure 15 shows the VR system “HoloStage” of Chuo University. Figure 16 shows the VR projector and display system. This system is composed of three large and flat screens and highperformance projectors corresponding to the screen. The luminance of the projector is 5000 lumen. The front and side screens are transmissive ones and the bottom screen is reflective one. VR space is created by projecting the image on the front and side screens, and the bottom screen as shown in Fig. 16.
Fig. 15 Immersive VR system HoloStage
Tsinghua Science and Technology, October 2008, 13(S1): 412-417
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tracking system. The positions of makers fitted to the liquid crystal shutter glasses and controller are tracked by the tracker device. Figure 18 shows a VICON tracker device. The 6 VICON trackers are provided in the 3D VR space surrounded by the three screens. Figures 19 and 20 show the liquid crystal shutter glasses and controller used by observer. In these figures, the white small ball denotes the marker. Fig. 16 VR space
2.3
Computer hardware and network
The HoloStage has a PC cluster system consists of one master-PC and four slave-PCs. The specifications of the PC cluster are shown in Table 1. The Giga-bit Ethernet is employed for the network of PC cluster. Figure 17 shows the network configurations. A slavePC computes the coordinates of location of viewpoint sequentially. Other three slave-PCs create the stereoscopic image from the view point rapidly.
Fig. 18
VICON tracker
Table 1 Specifications of PC cluster system Master-PC Machine
HP xw9300 Workstation
CPU
Dual Core AMD Opteron (tm) 2.4GHz
Memory
8GB Nvidia Quadro Fx4500 h2
Graphics card
Slave-PC h4 Machine
HP xw9300 Workstation
CPU
Dual Core AMD Opteron (tm) 2.4GHz
Memory
8GB Nvidia Quadro FX4500 h2
Graphics card
Fig. 17 Network Configuration
2.4 Tracking system Observer’s motion is captured by a system called VICON tracking system, which is the optics type motion
Fig. 19 Liquid crystal shutter glasses
Fig. 20 Controller
2.5 Method of stereoscopic view The binocular parallax is employed for the stereoscopic view. The stereoscopic view is realized in VR space by creating the image that corresponds to binocular retinal images, and projecting it to screen. In this system, the active stereo method employed for the method of the stereoscopic view. The liquid crystal shutter glasses weared by an observer is shown in Fig.19, which are synchronized to the computer display through infrared emitters alternating the left and right eye viewpoints at 120 Hz. The observer’s brain, as it does in the real world, combines the two views into a 3D stereoscopic image.
3 Visualization Using VR Technology It is difficult to understand the quality of shape model and mesh by the ordinal visualization technique. For this problem, The VR technology is applied to the visualization in pre-process. Figure 21 shows a
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
situation of verifying the quality of the mesh in VR space. Observer can see the stereoscopic image from the arbitrary view point by wearing the liquid crystal shutter glasses and operating the controller. Visualization using IPT has three merits. The first merit is that observer can see objects in multi scale from the entire to detail by using the large sized screen. The second merit is that observer can see in arbitrary view point by head tracking system. The third merit is that several observers can share the same image in VR space at the same time by only wearing the liquid crystal shutter glasses. From Fig. 21, observer can verify the quality of the shape and mesh for micro space by the visualization in VR space.
4
417
Conclusions
An urban modeling system using CAD/GIS data for the atmosphere environmental simulation was presented. The accurate shape model for landform and buildings can be prepared by the integration of several CAD and GIS data. The automatic mesh generation based on Delaunay method was employed. In order to verify the quality of shape model and mesh, the visualization using virtual reality technology, in particular IPT was introduced. The present method was applied to the actual urban area with complicated shape. From the results obtained in this paper, it can be concluded that the present system provides a useful planning and design tool to investigate the atmosphere environmental problem. References [1] Symanzik J, Cook D, Kohlmeyer B D, et al. In: Dynamic Statistical Graphics Workshop. Sydney, Australia, 1996. [2] Wegman E J, Symanzik J. Immersive projection technology for visual data mining. Journal of Computational & Graphical Statistics, 2002, 11(1): 163-188. [3] Taniguchi T. Automatic Mesh Generation Method for FEM. Morikita, 1992.
Fig. 21 A situation of verifying the quality of shape model and mesh in VR space
Development of an Accurate Urban Modeling System Using CAD/GIS Data for Atmosphere Environmental Simulation Tomosato Takada, Kazuo Kashiyama** Department of Civil Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan Abstract: This paper presents an urban modeling system using CAD/GIS data for atmosphere environmental simulation, such as wind flow and contaminant spread in urban area. The CAD data is used for the shape modeling for the high-storied buildings and civil structures with complicated shape since the data for that is not included in the 3D-GIS data accurately. The unstructured mesh based on the tetrahedron element is employed in order to express the urban structures with complicated shape accurately. It is difficult to understand the quality of shape model and mesh by the conventional visualization technique. In this paper, the stereoscopic visualization using virtual reality (VR) technology is employed for the verification of the quality of shape model and mesh. The present system is applied to the atmosphere environmental simulation in urban area and is shown to be an useful planning and design tool to investigate the atmosphere environmental problem. Key words: CAD/GIS; urban modeling; mesh generation; atmosphere environmental simulation; stereoscopic visualization; virtual reality
Introduction Recently, the atmosphere environment in urban area, such as strong wind flows around high-storied buildings, air pollution and heat island, is becoming serious problems. In order to investigate those problems, it is important to develop the method to evaluate the atmosphere environment accurately. The numerical simulation is a becoming powerful tool to evaluate that in accordance with the development of computer hardware and simulation technology. In the practical computation of this simulation, it is very important to prepare the accurate shape model and good finite element mesh in order to obtain the accurate numerical results. The finite element method is a suitable method for this type of simulation, since the finite element Received: 2008-05-28
** To whom correspondence should be addressed. E-mail: [email protected]
method can deal with the arbitrary shape of structures. This paper presents an urban modeling system using CAD/GIS data for atmosphere environmental simulation. Several CAD/GIS data are used for the preparation of shape modeling and an automatic mesh generation method based on the tetrahedron element in order to express the urban structures with complicated shape accurately. It is difficult to evaluate the quality of the mesh generated for the complicated computational domain by the ordinal visualization technique. In this paper, the stereoscopic visualization using virtual reality (VR) technology[1] is employed for the evaluation of that for urban structures with complicated shape in order to solve this problem. The immersive projection technology (IPT)[2] is employed for VR technology and the active stereo method is employed for stereoscopic view. The present system is applied to the atmosphere environmental simulation around Nihonbashi, Tokyo, and is shown to be a useful and powerful tool to investigate
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
413
the atmosphere environmental problem.
1 Modeling for Urban Area Figure 1 shows the flow chart of the modeling system for urban area. Modeling for landform Modeling for structures
Fig. 2 Grid surface and building polygon
Conversion to DXF file Combination of each model Fix the computational domain Surface mesh generation Visualization of surface mesh using virtual reality technology Verification of mesh quality 3-dimensional Delaunay method Solid mesh generation Fig. 1
1.1
Flow chart for modeling for urban area
Surface mesh generation for urban area
1.1.1 Modeling for landform For the modeling for the landform, two kinds of GIS data, the digital elevation maps (DEM) issued by Japanese geographical survey institute and 2D house maps (MAPPLE2500) are employed. For the DEM, grid interval is 5 m. Using the data of DEM, a more fine grid which is called as grid surface is created and the elevation at node is interpolated by the cubic spline interpolation method. Figure 2 shows the elevation and the polygon for the buildings obtained from 2D GIS data for buildings. Nodal points are generated on the boundary of building polygon at 2 m intervals and the nodal elevation is given by the interpolation using the nodal elevation data of the grid surface. Using the nodes on the ground surface, the ground surface mesh based on the triangular element is generated by the modified Delaunay triangular method[3]. Figure 3 shows the surface mesh on the ground for urban area.
Fig. 3
Mesh on the ground for urban area
1.1.2 Modeling for structures The urban structures are classified into two types: the simple shape model and complicated shape model. The different modeling methods are employed in this system. (a) Modeling for structures with simple shape The three dimensional shape for structures with simple shape is created by the extension of 2D horizontal shape to the vertical direction (see Fig. 4). The Building height is determined by the data of story of building. The height of one story is assumed to be 4m. The surface mesh is created to the side and top of the building. The structured triangular mesh is prepared for the side wall by the algebraic grid generation method based on Lagrange interpolation. For the top surface, the unstructured triangular mesh is created by the A structure with simple shape
Top part
Classification into two parts Mesh generation 2D boudaryof the building Side part Fig.4 Concept of the mesh generationmethod for structures with simple shape
Tsinghua Science and Technology, October 2008, 13(S1): 412-417
414
Delaunay triangular method because the shape of top is arbitrary in most cases. The shape modeling and mesh generation for the structures with simple are performed automatically by using the structure ID number, which is a unique number to discriminate each structure. (b) Modeling for structures with complicated shape For the mesh generation for urban structures with complicated shape, at first, the shape model is created using the CAD system accurately. Next, the surface mesh is generated by the Delaunay method (for top roof) and Lagrange interpolation method (for side wall). Figure 5 shows the surface mesh around the bridge and expressway and Fig. 6 shows the buildings with complicated shape.
structure model. Figure 8 shows the shape model of urban area without the expressway. In Figs. 7 and 8, the color structures indicate the shape model created by the CAD system. The red part denotes the expressway and the blue part shows the river. Figures 7 and 8 show the difference of landscape view by presence of the expressway. From these figures, the finite element model created by this method can be applied not only for numerical simulation but also for landscape simulation. Figures 9 and 10 show the landscape view. The purpose of numerical simulation is to understand the effect of the expressway to wind flow field.
Fig. 7
Fig. 5
Shape model of urban area
Surface mesh around the bridge and expressway
Fig. 8 Shape model of urban area not including the expressway
Fig. 6
Surface mesh around the building Fig. 9 Landscape view with the expressway
1.1.3 Data conversion to DXF file and combination of each model The data format of surface mesh for ground and building is converted to the drawing interchange file (DXF) data format. This conversion enables to combine the both mesh data by using the CAD system. Figure 7 shows the shape model of urban area after combination of the ground surface model and urban
Fig. 10 Landscape view without the expressway
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
415
1.2 3D computational domain In order to simulate for the atmosphere environment in urban area, the computational domain is fixed. Figure 11 shows the computational domain as numerical wind tunnel. In Fig. 11, the circle domain can rotate and it is possible to change the inflow wind direction same as experimental wind tunnel. The shear slip method is employed at the connecting domain to turntable. Figure 12 shows the mesh around the connecting domain. Figures 13 and 14 show exterior and interior view of computational domain. It can be seen that the fine mesh is employed near the turn table. 2 km
1 km
4 km
Fig. 11 Numerical wind tunnel
Fig. 14 Interior of computational domain
1.3
The mesh generation in interior domain is performed using the surface mesh data. The unstructured tetrahedral mesh is generated for the 3D domain by the Delaunay method.
2
Mesh around the connecting domain
Fig. 13 Exterior of computational domain
Virtual Reality System
Virtual reality (VR) is an important technology for the visualization in computer simulation. The quality of VR image is improved rapidly in accordance with the development of VR technology. Observers can see objects or physical phenomena 3-dimensionally by the stereoscopic view created by VR device. 2.1
Fig. 12
Finite element discretization in 3D domain
VR projector and display system
Immersive projection technology (IPT) is employed for VR technology and the immersive display is employed for VR display. Figure 15 shows the VR system “HoloStage” of Chuo University. Figure 16 shows the VR projector and display system. This system is composed of three large and flat screens and highperformance projectors corresponding to the screen. The luminance of the projector is 5000 lumen. The front and side screens are transmissive ones and the bottom screen is reflective one. VR space is created by projecting the image on the front and side screens, and the bottom screen as shown in Fig. 16.
Fig. 15 Immersive VR system HoloStage
Tsinghua Science and Technology, October 2008, 13(S1): 412-417
416
tracking system. The positions of makers fitted to the liquid crystal shutter glasses and controller are tracked by the tracker device. Figure 18 shows a VICON tracker device. The 6 VICON trackers are provided in the 3D VR space surrounded by the three screens. Figures 19 and 20 show the liquid crystal shutter glasses and controller used by observer. In these figures, the white small ball denotes the marker. Fig. 16 VR space
2.3
Computer hardware and network
The HoloStage has a PC cluster system consists of one master-PC and four slave-PCs. The specifications of the PC cluster are shown in Table 1. The Giga-bit Ethernet is employed for the network of PC cluster. Figure 17 shows the network configurations. A slavePC computes the coordinates of location of viewpoint sequentially. Other three slave-PCs create the stereoscopic image from the view point rapidly.
Fig. 18
VICON tracker
Table 1 Specifications of PC cluster system Master-PC Machine
HP xw9300 Workstation
CPU
Dual Core AMD Opteron (tm) 2.4GHz
Memory
8GB Nvidia Quadro Fx4500 h2
Graphics card
Slave-PC h4 Machine
HP xw9300 Workstation
CPU
Dual Core AMD Opteron (tm) 2.4GHz
Memory
8GB Nvidia Quadro FX4500 h2
Graphics card
Fig. 17 Network Configuration
2.4 Tracking system Observer’s motion is captured by a system called VICON tracking system, which is the optics type motion
Fig. 19 Liquid crystal shutter glasses
Fig. 20 Controller
2.5 Method of stereoscopic view The binocular parallax is employed for the stereoscopic view. The stereoscopic view is realized in VR space by creating the image that corresponds to binocular retinal images, and projecting it to screen. In this system, the active stereo method employed for the method of the stereoscopic view. The liquid crystal shutter glasses weared by an observer is shown in Fig.19, which are synchronized to the computer display through infrared emitters alternating the left and right eye viewpoints at 120 Hz. The observer’s brain, as it does in the real world, combines the two views into a 3D stereoscopic image.
3 Visualization Using VR Technology It is difficult to understand the quality of shape model and mesh by the ordinal visualization technique. For this problem, The VR technology is applied to the visualization in pre-process. Figure 21 shows a
Tomosato Takada et alġDevelopment of an Accurate Urban Modeling System Using CAD/GIS ...
situation of verifying the quality of the mesh in VR space. Observer can see the stereoscopic image from the arbitrary view point by wearing the liquid crystal shutter glasses and operating the controller. Visualization using IPT has three merits. The first merit is that observer can see objects in multi scale from the entire to detail by using the large sized screen. The second merit is that observer can see in arbitrary view point by head tracking system. The third merit is that several observers can share the same image in VR space at the same time by only wearing the liquid crystal shutter glasses. From Fig. 21, observer can verify the quality of the shape and mesh for micro space by the visualization in VR space.
4
417
Conclusions
An urban modeling system using CAD/GIS data for the atmosphere environmental simulation was presented. The accurate shape model for landform and buildings can be prepared by the integration of several CAD and GIS data. The automatic mesh generation based on Delaunay method was employed. In order to verify the quality of shape model and mesh, the visualization using virtual reality technology, in particular IPT was introduced. The present method was applied to the actual urban area with complicated shape. From the results obtained in this paper, it can be concluded that the present system provides a useful planning and design tool to investigate the atmosphere environmental problem. References [1] Symanzik J, Cook D, Kohlmeyer B D, et al. In: Dynamic Statistical Graphics Workshop. Sydney, Australia, 1996. [2] Wegman E J, Symanzik J. Immersive projection technology for visual data mining. Journal of Computational & Graphical Statistics, 2002, 11(1): 163-188. [3] Taniguchi T. Automatic Mesh Generation Method for FEM. Morikita, 1992.
Fig. 21 A situation of verifying the quality of shape model and mesh in VR space