Objective

2

CAD(Computer Aided Design) is widely applied in many areas; however

rapidly rendering a large-scale CAD model on a commodity personal computer remains a challenge. Many researchers have been working on general-purpose rendering methods for large-scale models

and some have evaluated special-purpose rendering methods by utilizing the features of target models. The presented method belongs to special-purpose rendering methods. The method is designed to render a large-scale repeated-structure model

which is constructed by arranging several basic objects according to certain rules.

Method

2

Tree is often used to represent hierarchical CAD models. Two special nodes are defined to represent repeated-structure CAD models. One is used to represent basic objects

and the other is used for the "arrangement rule" of basic objects. A large-scale repeated-structure CAD model can thus be represented with a small-scale tree. CAD models cannot usually be rendered directly; they are to be converted into facets for rendering. However

the corresponding facet models for large-scale CAD models are extremely large to be stored and processed

which is a significant problem for large CAD model rendering. Repeated-structure CAD models are constructed by arranging few basic objects according to some rules. Therefore

the presented method solves the problem by generating and storing only the facets of basic objects

and the facets of all other objects are generated during the rendering process according to arrangement rules. Basic objects are less than the total objects in CAD models

and facets of basic objects are thus easy to generate and store. The running time of the view-frustum culling algorithm is proportional to facet number. For a large number of facets involved in large-scale CAD model rendering

the efficiency of the view-frustum culling algorithm is necessary to improve. Instead of processing facets directly

the presented method culls objects layer by layer by utilizing the hierarchical structure of repeated-structure CAD models. Accordingly

most objects can be processed in a high level

and only small part of objects is left to be processed in the facet level. The presented view-frustum culling algorithm is implemented by combining hierarchical structure features of the repeated structure CAD model and the render-to-texture functions of a modern GPU. The algorithm can select target objects rapidly

which is another contribution to rapid rendering.

Result

2

The presented method is implemented on the basis of ACIS

OpenGL

and HOOPS in Visual Studio 2010

and all testing is performed on a computer equipped with 3.20 GHz CPU

4.0 GB RAM

NIVIDIA GeForce GT740 GPU

and Windows 7 operating system. The presented method is integrated into SuperMC (Multi-physics Coupling Analysis Modeling program)

which is a self-developed nuclear simulation program. SuperMC is often used in processing full reactor core models

which are typical repeated-structure CAD models. Thus

three full reactor core CAD models

namely

HM

ADS

and DCA

are selected for testing

which consist of 1 114 384

113 952

and 20 808 entities

respectively. For the three full reactor core models

the presented method performs best on the HM model and performs worst on the DCA model. HM is considerably larger than DCA. The presented method is designed for large-scale models. In comparison with the traditional rendering method

the presented method exhibits better performances on all the three models

it can achieve about three times rendering speed increase for far-view rendering. Although the presented method and the traditional method can achieve similar rendering qualities

the presented method can achieve a higher rendering rate

especially for far-view rendering. The test result demonstrates the effectiveness of the presented method.

Conclusion

2

The development of general-purpose rendering methods for large-scale CAD models remains a challenge. This paper presents a special-purpose rapid rendering method

which can render a large repeated-structure CAD model

according to the features of repeated-structure CAD models. The developed method is integrated into self-developed software SuperMC for application. Three full reactor core models based on SuperMC are used for testing. The presented method can achieve a good rendering quality and a high rendering rate than those of the traditional rendering method

which demonstrates the effectiveness of the presented method. Only "array-arrangement rule" is currently supported by the presented method; thus

to support more "arrangement rules" is our future work.