Hidekazu Hirayu, Japan | ISBN: | Submitted: Apr 30, 1999

Constructing the "Historic Villages of Shirakawa-go" in Virtual Reality

Constructing the “Historic Villages of Shirakawa-goEin Virtual Reality

Hidekazu HIRAYU*1, Takeo OJIKA*2, Ryugo KIJIMA*2, Takayuki*3 HASEGAWA, Munemoto HIRAKO*4

*1Gifu Prefectural Research Institute of Manufacturing Information Technology, 4-179- 1 Sue, Kakamigahara 509-0108, Japan, and Softopia Japan, 4-1-7 Kagano, Ogaki 503- 8569, Japan, hirayu@gifu-irtc.go.jp *2Faculty of Engineering, Gifu University, 1-1, Yanagido, Gifu 501-1193, Japan, Ojika@ojk.info.gifu-u.ac.jp, kijima@vsl.gifu-u.ac.jp *3Graduate School of Engineering, Gifu University, 1-1, Yanagido, Gifu 501-1193, Japan? hasegawa@vsl.gifu-ua.ac.jp *4Graduate School of Engineering, Gifu University, 1-1, Yanagido, Gifu 501-1193, Japan , and Aeroworkshop Inc., Techno Plaza 301, 4-179-1 Sue, Kakamigahara 509-0108, Japan, hirako@kakamigahara.com

Abstract: In Japan, there are nine sites that have been registered by UNESCO as World Heritage. Among them, Shirakawa-go and Gokayama in Gifu and Toyama Prefectures was the sixth registered site in our country. The special private houses in this region, called “Gasshyo-zukuri,E were isolated from the outside world influences, hence they developed a unique design built to endure the severe natural environment These houses are a great spectacle because of their construction and culture. Our research involves the development of a Virtual Reality version of the entire Shirakawa-go region in Gifu Prefecture to protect, preserve their original construction and educate people about this valuable world property. Our research has been divided into 3 sections. (1) The first section uses aerial photographs to make a 3D version of Shirakawa-go, which covers 45.6 hectares. To make the 3D model, we took aerial photographs from an altitude of 2000 meters. (2) The second is a 3D version of an area called “MinkaenE which covers 5.8 hectares in Shirakawa-go. This area has many “Gasshyo-zukuriEbuildings originally built (but later destroyed) from another region, and so restructured in this area. To make this 3D version, we took aerial photographs of the area from an altitude of 750 meters and photographs of “Gasshyo-zukuriEstyle house from all sides. (3) Finally, we modeled a typical Gasshyo-zukuri house within the Minkaen area from its original drawings. This model has enough structural detail to enable a virtual walk-through of the house.

1 Introduction

At present, there are 582 properties in 156 countries (December, 1998) all over the world that have been designated by the World Heritage Treaty of UNESCO. Of the nine properties in Japan we have focused upon the "Shirakawa-go and Gokayama" in Gifu and Toyama Prefectures, respectively [1]. In this region, the wind is strong due to its topography, and the region has one of the heaviest snowfall zones in Japan. In winter they have as deep as four meters of snowfall annually. The private houses in this region have a peculiar form called "Gasshyo-zukuki". The followings are the characteristics of "Gasshyo-zukuri"[2,3,4].

1. Steep roof pitch: for the shedding of heavy snowfall 2. Multi-layered roof (using an enlarged space, they raised silk and performed other activities inside the house) 3. A nail-less wooden infrastructure (a restorative structure, even if the roof is removed by the wind, the structure can be restored) 4. The windows are located north and south to prevent the wind damage (the structure enables the wind to blow through the house).

The country and the prefecture with the World Heritage sites, which are recognized as world valuable assets, should take important responsibility for preservation and protection of the properties, and maintenance and improvement of the environment. In order to utilize protection and education of World Heritage sites[5,6,7,8,9,10], digitization of them are in progress in many research institutes, etc.. In this case, it is necessary to preserve not only externals and shapes of the sites, but also various cultural aspects of the cultural assets. However, the World Heritage sites, where people are actually living now, like the "Shirakawa-go and Gokayama" are very few, and it is difficult to reserve its original forms and to keep privacies of the residents. Thus, preservation by Virtual Reality (VR) is becoming very important recently. From this viewpoint, we examined the necessary procedure and techniques for digitization of external views and cultural aspects of "Shirakawa-go" by using VR technology[11]. And, we also report the reconstruction of "Shirakawa-goEarea in “Shirakawa-go and GokayamaEin 3D.

2 The technique of the modeling

In this research, since it was difficult to make the three dimensions of entire Shirakawa-go at a time, we divided the all area into three parts ---(1) the panorama of Shirakawa-go and its surrounding area with approximately 45.6 ha, (2) the part “MinkaenEwith approximately 5.8 ha in Shirakawa-go, and (3) as a detail view, a typical Gasshyo-zukuri house with steep roof and eaves in the Minkaen. The flow of the processing of each technique is shown in Fig.1. (1) We made the overall view of VR Shirakawa-go by using an aerial photograph digital system (APDS in short, PHODIS of the ZEISE Co.) on the basis of the aerial photographs. For the texture data we used the full colored aerial photograph as it is. (2) As for Minkaen, we modeled it by using original architectural blueprints. We use the aerial photograph for its texture data. (3) Regarding many Gassyho-zukuki, we modeled them by two methods. One is a method of making the models on the software by using the architectural drawings. The other is a method of making models on the software by using photographs which were taken from surroundings of each Gassyho-zukuri. And for the texture data, we used the color photograph of the Gassyho-zukuri. To experience walking in virtualized Shirakawa-go, Minkaen and Gassyho-zukuri, we made the VR system which was written by C language and IRIS Performer Ver. 2.2.

Fig.1 On the method for three dimensions

2.1 The construction of the panorama of Shirakawa-go

To make the model of Shirakawa-go, we input the photograph taken from the high degree of 2,000 meters and then, we obtained the height information about the village. It then generated an enormous three-dimensional information and polygon model. Therefore, when such a huge dataset is loaded on the VR system, the frame rate becomes clumsily slow, and hence the user can’t comfortably experience the Shirakawa-go model. Therefore, we tried to reduce the polygon numbers. Here, the color images by the aerial photographs are used as the texture data.

2.1.1 Construction procedure of 3D Shirakawa-go

Basic policies and operational procedures of 3D Shirakawa-go are as follows (Fig. 2). ?Basic Policies? To make 3D Shirakawa-go, we executed the following basic policies. · The amount of data ( The number of polygons and the amount of textures ) should be restricted so that the VR system can manage. · By mapping the aerial photographs on VR Shirakawa-go, the realistic images are applied. ?Operational Procedure? 1. Scan many aerial photographs with the accuracy of 900dpi. 2. Specify the plane coordinates value of the targets and the signpost fixed points in the each aerial photograph. In our research, we specified six signpost fixed points in each aerial photograph which is in the range of 1.8 kilometers East and West, and 1.6 kilometers North and South, respectively. ) 3. Analyze digitally the plane coordinates and the altitude values, using the PDAS. The measurement using the photograph is basically the same principle as a triangular measurement. 4. Make the Geographical features model using many polygons. 5. Reduce the polygons in geographical features model. 6. Output the ortho-photo image. 7. Map the ortho-photo image as texture data on the geographical features model. 8. Output to the Open Inventor file format.

Fig.2 Outline of the system ( 3D Shirakawa-go )

2.1.2 Result of 3D Shirakawa-go As the result of making 3D Shirakawa-go modeled by the DXF format, the file size of the model and its polygons size with 5 meters mesh for the area 1.8km * 1.6km were about 56MB and 230,000, respectively, and ortho-photo as texture was about 260MB. The amount of data is too heavy to realize walk through in 3D Shirakawa-go. Thus, we did their reductions by uniting many polygons with the same heights into a larger one, and by decreasing the resolution of the texture data As its result, the file, polygon, and texture sizes of the model are reduced to about 2.4MB by the Open Inventor format, 28,000 polygons, and about 2.7MB, respectively. The example of the reduced result is shown in Fig.3. The example of the displayed result is shown in Fig.4.

Fig.3 The reduction of polygons ( wire frame ) .

Fig.4 The display of 3D Shirakawa-go modeled.

2.2 The construction of 3D Minkaen

Minkaen is an area where there are many Gasshyo-zukuri style houses which had to be moved because of a dam being constructed nearby. We made the geographical features data based on the drawings used to establish this area. And, the color images by the aerial photographs that were taken by helicopter from 750 meters height are used as the texture data.

2.2.1 Construction procedure of 3D Minkaen

Basic policies and operational procedure of 3D Minkaen are as follows (Fig. 5). ?Basic Policies? To experience walking in Virtualized Minkaen on VR system, we had to reproduce the accurate landform such as road, square, and hill in this area. Therefore, the enormous aerial photographs are required in order to make the model using aerial photographs. And we judged that it was difficult to extract the height of ground accurately using the digital analysis system to the aerial photographs, because a lot of trees were interrupted to see surface of the ground in Minkaen precisely. To make 3D Minkaen, we executed the following basic policy. · The amount of data ( the number of polygons and the amount of textures) should be restricted so that the VR system can manage.. · By mapping the aerial photograph on 3D Minkaen modeled, the realistic images are applied. · The geographical features data is made by using the topographical map of 1/500. ?Operational Procedure? 1. Scan the aerial photograph ( to use as the texture data, we scan the aerial photograph which was taken from the high degree 750 meters above Minkaen. ), and make the ortho-photo image. 2. Digitalize the topographical map( scan the drawings of Minkaen ) 3. Make the Geographical features model. 4. Map the ortho-photo image as texture data on the geographical features model. 5. Locate many Gasshyo-zukuri houses which only the outsides were modeled ( in Chapter 2.3 ) on the geographical features model. 6. Output to the Open Inventor file format.

Fig.5 Outline of 3D Minkaen.

2.2.2 Result of 3D Minkaen As the first result of making 3D Minkaen modeled by the Open Inventor format, the files of the model and ortho-photo as texture were about 5.3MB and about 550KB, respectively. Then, we tried to reduce them by the same technique as in the 3D Shirakawa-go case. Then the sizes of the model are reduced to 460KB by the Open Inventor format, 5,600 polygons, and 670KB for ortho-photo, respectively. Digitalization of topographical map, the example of the geographical features model, the example of the display result are shown in Figs.6-8, respectively.

Fig.6 Digitalization of topographical map.

Fig.7 The geographical features model of 3D Minkaen.

Fig.8 The display of 3D Minkaen model.

2.3 The construction of 3D Gasshyo-zukuri

To experience walking into Gasshyo-zukuri in Minkaen on VR system, we constructed two kinds of models. Eight of nine Gasshyo-zukuri houses only had the exterior modeled. The other is one 3D Gasshyo-dukuri whose details in the house such as many columns and beams are realized in detail.

2.3.1 Construction procedure of 3D Gasshyo-zukuri 1) For the Gasshyo-dukuri whose exterior are just modeled We took the photographs of about ten photographs per one Gasshyo-dukuri from all sides(four photographs from diagonal, four photographs from the front and side, two photographs from the other). And we modeled nine Gasshyo-zukuri houses by the software ED Builder Pro Ver. 2.0Eof 3D Construction Co.. We used front face and side photograph of nine Gasshyo-zukuri as the texture data. And preserved the 3D Gasshyo-dukuri models into the Open Inventor file format. To experience walking through Shirakawa-go, Minkaen and Gasshyo-zukuri on VR system, VR system can read all data by the Open Inventor file format.

2) For a Gasshyo-dukuri with detailed features The house was made on the basis of the drawings which had been written when the houses were being relocated. As a software for the 3D CG, we used ED Studio MAX ver. 2.5Eof Autodesk Co.. And, its texture data are taken from the actual photographs of the house.

2.3.2 Result of 3D Gasshyo-dukuri The file sizes of the resulting model of the 3D Gasshyo-dukuri were about 4.4MB, 130,000 polygons, and about 2.4MB for the texture data, respectively. And we can easily walk through inside of the VR Gasshyo-dukuri. The examples of the wire frame of the 3D Gasshyo-dukuri, the appearance of the house, and its inside are shown in Figs.9-11, respectively.

Fig.9 The wire frame of 3D Gasshyo-dukuri.

Fig.10 The appearance of 3D Gasshyo-dukuri.

Fig.11 The inside of 3D Gasshyo-dukuri.

3 Conclusion In this research, to protect and preserve the original constructions, and to educate people about a valuable world property, we made a virtual World Heritage sites “Shirakawa-goEby using the modeling methods which are reconstructed from the aerial photographs, the ground photographs, and the drawings. And we could realize the walk-through of Shirakawa-go, Minkaen, and Gasshyo-dukuri by using this system. And, when modeling a wide area like Shirakawa-go, we confirmed that our modeling methods using the landform digital analysis and ortho-photo mapping by the aerial photographs are effective for the following reasons. (1) The man-hours (the cost) for inputting the landform shape are fewer than the existing digitalization of topographical map. (2) Since the material used to make the geographical features model is the same as that of the ortho-photo data, it is easy to obtain the mapping material. (3) Since the same coordinates for ortho-photo and the geographical features model can be obtained at a time, it is possible to realize the accurate projection. (4) By mapping the aerial photographs, it is possible to reproduce the scene images realistically.

Acknowledgements The authors would like to thank Mr. Kenji Yajima, Dainichi-consultant Inc., for the digitalization of Shirakawa-go and Minkaen model, and Ibisoku Inc. for taking the aerial photographs of Minkaen. A part of this research was supported by Gifu University and Softopia Japan. We also would like to express our gratitude to them.

References [1] Hietsu-gasshyo cultural society ( Kadotake, Takada, Hasegawa ): Gassyou-zukuri villages as World Heritage, Gifu Newspaper Inc., (1996). [2] Gasshyo-dukuri villages as World Heritage commemoration business execution committee: Gasshyo-zukuri villages in Shirakawa-go and Gokayama, (1996). [3] Miyazawa,Kawamura: Restore Gasshyo-dukuri, The foundation outdoors museum of Minkaen, (1998). [4] Miyazawa: Gasshyo-zukuri is reasoned, Shirakawa village and Shirakawa Village Board of Education, (1995). [11] H.Hirayu et al., Construction of UNESCO World Heritage “Historic Villages of Shirakawa-go and GokayamaE, Proc. of the Second VRSJ Annual Conference, pp.83-84 (1997).

[more information]
http://www.virtualheritage.net/library/archive/37hirayu.htm

[other authors]
Takeo Ojika

[keywords]
Virtual World Heritage, World Heritage, UNESCO, virtual reality, shirakawa