# Spatial Data-Based Automatic and Quantitative Approach in Analyzing Maintenance Reachability
## 2 Literature Review  
Recent publications that are relevant to the proposed method are concerned with three research streams: maintenance and maintainability, virtual maintenance technology, and maintenance reachability analysis. In this section, relevant studies were summarized. For maintenance and maintainability, these two closely related concepts influence each other in practical engineering. Maintenance is a kind of work undertaken by maintenance personnel to maintain or restore the product to serviceable condition, and maintainability is a design character taken by designers in the development process to combine the features of improving the convenience of maintenance into the product design [14]. In order to facilitate maintenance, the maintainability design should start from the early stage and emphasize early intervention. Generally, maintainability requirements cover qualitative and quantitative sections. Specifically, qualitative design and analysis are conducted by maintainability check, and quantitative design and analysis are conducted by allocation  
Figure 1: Overall Structure. and prediction. In recent years, advanced maintenance technology has been introduced, for instance, the intelligent predictive maintenance is more in line with the industrial development trend, such as condition-based maintenance, prognostics and health management, and remaining useful life estimation [15], and this maintenance policy has been adopted by many industries in various domains. In this advanced maintenance method, intelligent sensors are extremely essential for the realization of predictive maintenance [16; 17; 18]. For virtual maintenance technology, a variety of studies have been conducted since the late 1990s. The advent of virtual reality technology provides better support for maintainability. The current research on virtual maintenance technology focuses on the following aspects: virtual maintenance prototype modeling [19; 20; 21; 22; 23], virtual simulation action process generation [24; 25; 26], maintenance training [27; 28], product design [29; 30], and maintainability evaluation under virtual simulation [31; 32; 33]. For virtual maintenance prototype modeling, an approach to the network-centric virtual prototyping in a distributed design environment was presented by [PERSON] [21]. The approach has combined the virtual assembly modeling and analysis technique with distributed computing and communication technology for supporting the virtual prototyping activities over a network. A virtual maintenance system was developed and the flowchart of the model transformation technology was designed by [PERSON] et al. [22]. Moreover, a virtual reality environment prototype of a building management system for maintenance activities was implemented by [PERSON] et al. [19]. For example, a low-cost VR application for maintenance training, which is an object-oriented prototype desktop VR-enabled system for maintenance (V-REALISM), is presented by [PERSON] et al. [28]. A low-complexity method is proposed to author an interactive virtual maintenance training system of hydroelectricity-generating equipment [27]. For instance, on the maintainability evaluation under virtual simulation, Lockheed Martin eliminated the metal models that had been used for design research and used virtual maintenance technology based on the CAD model to conduct an analysis on the maintainability evaluation, verification, and human factor when designing the fighter system of the F-16 [33]. A systematic approach for human factor automatic evaluation for the entire maintenance processes in the virtual environment was proposed by [PERSON] et al. [32]. A time prediction method of the assembly and disassembly of the product maintenance process was proposed by [PERSON] et al. on the basis of virtual maintenance [31]. Recently, augmented reality technology has been widely used in maintainability evaluation and verification.