中国古建筑风格初探(英文)(2)

Figure 5 sampling

above four) and sampling frequence must be considered

cloud consisting of discrete vector distance points on the surface of the object. Points of set is joined in different ways can get different 3D model, so the main work for 3D model reconstruction is to extract characteristic points, based on which characteristic lines and surfaces are constructed, and finally three dimensional object is reconstructed. A lot of manual operation is in need since automation level is not that high at present.

2.2 Components Modeling

For the moment, there are several ways for 3D modeling, such as laser scanning and image-based approaches which means processing digital image by computer, 3D identification and measurement realized calculating all elements by computer and do rectification. Semi-automatically or manually finish the extraction of image geometry and physical information, and this method is widely applied in digital city modeling field. By collecting texture with digital camera, after texture projection, building looks next to the real landscape.

Those small-scale scenes, which are demanding in architectural detail and need to display special relationship between indoor and outdoor space, are often constructed through “true-3D”, such as CAD technology. Digital CAD Modeling can create visual geometric models that simulate the three dimensional form of a building or architectural detail. Once a digital model is constructed it can be used to generate elevations, sections, plans, and perspective views. It can also serve as a base for walkthroughs, flybys, and virtual reality tours

3D model in Cad system has two expressive ways: volume-based and surfaced-based. Volume-based model is expressed by so-called CSG tree, this method makes a hypothesis that the object to be expressed is constituted by some basic units, (such as sphere, cube and cylinder etc.), Namely, DIVIDE and CONQUER, constitute a complex 3-dimensional object through regularization BOOLEAN algorithm (parallel, intersection and subtraction).

Timber-structure buildings’ components are regular on the average, they can be constructed by simple edition and operation of basic units, and the difficulty of component modeling lies in curved-surface structure modeling. Construction of the curved-surface structure in computer is constructed by simulation through plane. Because CSG model doesn’t contain parameter-curved surface, it has difficulty in expressing details with curved surface, such as column. In consideration of structure, circle centers of the upper and low cross section are not in the same vertical line, its cross section is elliptical, and so it can’t be constructed through cone, a basic unit. The way out in this paper is: the ellipsis can be simulated through the convex polygon at first, then construct a curved-surface structure with straight texture through the up and bottom ellipses, along which then use a bounding volume to do SLICE operation. One column needs 3 to 5 sections; they are joined through BOOLEAN algorithm. The bigger the simulating segmentation parameter SURFTAB1 of convex polygon, the more the structure result approximating to the column itself, and

the bigger the amount of data. To meet the need of collision detection in late period, simulate parameter if all components should have the same standard in the process of modeling.

Other structures with curved surface can be obtained through Boolean algorithm of some basic units and cross-section EXTRUDE operation. The following methods can also be applied to construct other more irregular curved-surface structures so long as getting enough characteristic points.

Concave curved-surface structure modeling is more tough, like BaoZhuCi, the surface integrated with the pillar is not regular, its modeling can be obtained by Boolean algorithm of constructing convex curved-surface structure through

characteristic points.

Figure 6. component model

2.3 Hierarchical Model and Integrated Model

After the completion of components model construction, components location and component integrating into a building model in CAD. Its position is decided by its coincidence with the geometrical center location in building blueprint as well as bottom surface Parallel. Although timber-structure building is complicated in structure but discernible in hierarchy. Data organization can be done hierarchically, forming column basis layer, DouGong layer, frame layer, roof surface layer roof layer and decoration layer, then combine layer models into an integrated one.

Chinese timber-structure building is Centro-symmetric, components should follow certain modules, and modeling technology of utilizing block operation can significantly reduce workload and model’s data volume. The block technique was the driving method to construct the whole model. “Block” objects allow adjusting parameters of different dimensions of an element to compose variations of the same element. Similar components at various locations were constructed once, and then used many times.

Figure 7 hierarchical model

Figure 8 integrated model

2.4 Database of Buildings

Every component is given a special serial number and saved into a database system, table of database looks as followed (figure9-10). Geometry information will be collected automatically by system, and attribute information must be written by architects. In practice, the database includes also a lot of videos archives, all words which narrate functions and features of components can be made for commendatory of video archives. First components will be saved into database after sampling and modeling, if error happen during the process of simulating assembly, the component should be modified and

length width height vol. location …

X.Y.Z … renew the old one in the system.

Figure9 table 1

Figure 10 table 2

The important function of the database system mainly includes two factors: one is used to record, another is used to support exploitation again.

3. SIMULATING ASSEMBLY

Based on components acceptance by using cad software and construction of database, imitation assembly process by computer can begin. It aims at recording timber’s assembly order, examination 0f motise-tenon construction and DouGong’s complicated and tricky assembly process, so that it can provide real and detail data for renovation, reconstruction, study and protection of future timber-structure buildings. This process is achieved by the usage of 3DS MAX.

3.1 Making Texture

The main task of generating material texture is to determine the color, texture and light and shade pattern of the material.

Texture describes the natural characteristics of the surface of an object, it can be generated by a 2D random function f(u,v), and also can be from a scanned image or generated by a graphic package. The feeling of actually texture should require help of digital camera, all surfaces of objects will be sampled ,and all map which has been dealt with in the Photoshop attach to object orderly, this work can be completed by multi/sub-material in 3DS MAX.

In fact, kinds of rich effects video can be produced by varying material in 3DS MAX, such as wash-drawing-style (a light tint or hue) video with artistic sense through falloff material

mapping, industrial effect videos through final render material mapping ,etc. (Figure 12)

Figure 11 true texture Figure 12 industrial effect

3.2 Order of Assembly

Assembly order of timber-structure building has strict construction processing, although some components’ order can

be reversed mutually, but in general, most follow the order of first the internal then the external, first the bottom then the top.

In terms of form, timber-structure building’s simulating assembly is a dynamic visible process. In line with the assembly

order, that’s, from the bottom to the top, from the internal to external, component models are packed into integrated model along certain movement orbit. In the beginning, the integrated