## 3 High-Fidelity Digital Twin Construction Methods
### Digital Twin Data Mapping Methods  
The ultimate goal of the digital twin is to provide real-time, efficient, and intelligent services such as monitoring, diagnosis, and decision-making, which require a large amount of data. In addition, the digital twin model is also a dynamic rather than static model and requires data access to update the model dynamically. That is, twin data is the key to the digital twin system. In the process of constructing a digital twin system, due to the diversity of devices in hardware, software, connection mode, and communication protocols, i.e., data acquisition mode, the data has the characteristics of multi-source heterogeneity, which is eventually manifested in the phenomenon of data silo including the physical level and the logical level. The so-called physical data silos, that is, in the data at different stages, different departments independent of each other store and maintain the formation  
Figure 5: The workflow of the behavioural model. of the physical sense of the island. The logical data silo refers to the same data in the definition, and the understanding will be different because of different stages, equipment, departments etc., that is, the data in the logical semantics can not interact. [PERSON] et al. [25] proposed a method to map the digital threads in shipbuilding and use them for the digital twins to create a consistent data model and optimise the process control. To solve the data silo problem of industrial equipment, this paper is based on the OPC UA information model [26] and proposes to instantiate the information model of centring turning processing according to specific application scenarios, represent the events and data of the processing process as an object, and give the object variables, events, and methods, and realise the interconnection between these things through the referencing, and ultimately form a set of standard data parsing and organisation models to learn the semantic interoperability of multi-source and heterogeneous data. Semantic interoperability of heterogeneous data. OPC UA technology is used to map the information objects to the address space, the description and access to process data is realised through OPC DA, the report and access to vertical data is learned through OPC HAD, and OPC A&E provides the information interface of running events and alarms. 1. Centring process information model  
In this paper, the standard machine tool manufacturing information model is modified and extended to propose the information model of the centring turning machining process, and the tree structure is used to describe it, as shown in Figure 6. The information model has three elements: information object, attribute, and attribute set. Among them, information objects are conceptualised descriptions of real or abstract entities of the machining process, such as spindles, chucks, and process documents. Attributes are textualised or digitised reports of the nature and characteristics of the information objects. An attribute set is a collection of features. The information model is instantiated according to the above definition to obtain the centring machining system information model with practical significance, as shown in Figure 6.  
2. Data communication scheme based on OPC UA  
OPC UA is a new generation of service-oriented cross-platform transmission and transmission process security communication solution in the manufacturing field developed based on OPC Classic, which supports a variety of data semantics and information models and can unify the communication mechanisms and data interaction modes of different industrial devices to solve the data transmission and communication problems of  
Figure 6: The information model of a digital twin for the high-precision lens centring process. processing. C/S structure, i.e., client/server structure, is adopted to realise the OPC UA system. The OPC client we built includes application programs, communication stacks, and client APIs to send and receive OPC UA service requests to and from the OPC UA server.