The Existence Of Computer Aided Design

Published Date: 02 Nov 2017

Among all this technologies, Internet-based collaborative CAD has not received much attention from the research community. Internet based collaboration can be organized as either a horizontal or a hierarchical systems. Horizontal collaborative CAD technologies are mostly focused on synchronous integration of heterogeneous design data, processes, and software systems over the Internet. They either apply sophisticated interfacing technologies to connect multiple CAD systems [4], or develop proprietary framework for networked CAD [5]. On the other hand, most the work concerning CAD integration in the hierarchical category was based on improving the diverse systems of data design among different kinds of activities in a product life cycle. However, most of the technology developed for horizontal and hierarchical systems did not fully addressed the issues of CAD data transfer, especially large files transfer across the networks with limited bandwidth, which is a problem that needs attention. Also, most of the collaborative CAD systems employs File Transport Protocol (FTP) functions with the addition of some security features for data exchange and some sellers claim that their systems uses 3D streaming for distribution of CAD models, meanwhile they are using the streaming method originally built in computer graphics, which transmits triangular meshes from simplified to complex level, this is also known as progressive meshing [4].

The problems encountered among designers is that CAD models are always too lag and are not easily transfer in collaborative environments. The following problems were encountered with CAD transfer over the network: The size of data file CAD models to be transmitted is generally quite larger than that of the other data file over the internet; The CAD model data are progressively modified and updated until the final design is finally fixed and due to the large size of model data, there is a significant delay during the transmission over the network (Rong et al, 2005). In addition, security in collaborative product design security is another important issue, since the important technologies of a company could be stolen whistling exchanging design data. Using Virtual Reality Modelling Language (VRML) and X3D, only the information for the mesh is received, leaving out the information of the assembly and design features. However, most company would not let out any part of the product data [8].

According to the approaches discussed in this paper for 3D streaming technology, the Multi LOD method is compared with the progressive mesh system to show a well-argued discussion on why one method is better than the other. The rest of this paper is organized as follows. The second section will discuss the literature review of the recent computing technology for CAD and there approaches/methods. The third section will particularly talk about 3D streaming technology based on multi LOD and mesh simplification methods for visualizing 3D objects in the Web. Section four will present the discussion on both methods, which will lead to the conclusion.

2.0 literature review

2.1 3DCAD Mesh Simplification

In the last decade, there has been an active research and developments carried out on mesh simplification problems. The simplest simplification method called the vertex decimation was proposed by Schroeder et al. the approximation error was estimated many times using the distance between the vertex and average planes. A majority of the vertex decimation methods use more precise error metric, i.e. the localized Housdorff error. However, these methods delete all associated triangle of vertex, so we need to perform additional re-triangulation. A relatively stable iterative contraction algorithm has become the most popular method developed, compared to vertex decimation. The vertex pairs (vi, vj) were continuously collapsed and generates new vertices at each iteration until a satisfied error is created [13].

PM [Hoope 1996, 1998] proposed the first progressive compression technique. The operations carried out on edge collapse, simplified the initial mesh to the base mesh. An edge collapse operation removes a vertex at a time, the information relating to the connectivity and geometry of the removed vertex are stored in the refinement [3]. A more detailed research was developed by many researchers, but there are two issues that need to be addressed in the edge collapse simplification method. An important error metric Cv that is used to prioritise the collapse need to be determined. In addition, the location of the newly generated vertex Vnew needs to be calculated. Various mesh simplification methods were developed, but the methods did not satisfy some needs in the mesh simplification applications. The desired methods must be capable of handling multiple features contained within the mesh model. A reasonable error level specified must be preserved within a reasonable time limit even in highly approximated models [13].

Recently, an improved mesh simplification method was proposed, these uses curvature values as an added features and also minimises the accumulated error by locally optimizing the position of new vertices during edge collapse [13]. This method for mesh simplification will be discussed further in section three.

2.1 3DCAD Level of Details (LOD)

Recent research work [9] has shown that users’ requirements should be used to define configurable product view.

Different types of established product views need to be presented to them, depending on where they are active in the

organization [8]. This idea is applicable throughout most stages of a product lifecycle. In collaborative product

development, not only designers geographically dispersed are likely involved, but other stakeholders such as customer,

suppliers, and technology providers may also participate the development process at different phases. The findings. I stop

It is to the manufacturer’s advantage that the supplier can only

gain access to the part model being outsourced and possibly some others interfacing with it. Sensitive design

information or critical components need to be hidden from the supplier. The product owner should be able to freely

choose the design content to be obscured. Intellectual properties can be well protected in this manner. In addition, the

size of data transmission over the network is reduced during design collaboration if the models can be simplified as a

result of eliminating the unnecessary or hidden information.

Therefore, this research argues that a product model should be categorized into variants rendered for different

stakeholders considering their individual role and the time they join the collaboration. Fig. 1 illustrates such an idea

about level of detail (LOD) for 3D model. LOD in this regard indicates assess control of design features at different

levels. In contrast, the previous LOD methods that are derived from mesh refinement treat CAD model as a whole in

geometry categorization. As a result, they cannot control display/hiding of design features in an explicit manner. Our

empirical studies show that protection of information sharing in distributed collaborative product development should

be put into the context of design semantics. Certain design features must be completely obfuscated in order to avoid

leak of company intellectual properties. The mesh model only visually in a coarse resolution, cannot serve the purpose

well [15].

Fig. 1. Levels of detail (LODs) in 3D product model [15].