# Seeking a Definition of Digital Twins for Construction and Infrastructure Management
## 4 Potential Benefits of DTs for Construction and Complex Infrastructure Management  
There are many definitions for DTs and each definition can be linked to different benefits. [PERSON] et al. [46] define a DT as a digital representation of the infrastructure [39]. [PERSON] [15] goes deeper and divides the DT concept into prototypes, instances, aggregates and environments. According to [PERSON], a Digital Twin Prototype details the main information of the real objects in the digital environment, such as 3D properties or detailed specifications. The Digital Twin Instance, second type, is always linked to the real management of the object or asset. One step beyond is the Digital Twin Aggregate, which all the data captured by the Digital Twin Instance is analysed and even linked to sensors. At last, [PERSON] details the Digital Twin Environment, which is the final step to achieve a complete DT concept with real time data, real time analysis, and even predictive maintenance. As indicated above, DTs have different implementation levels, starting as a 3D representation with data hosted in it, which could also be seen as a BIM model. The user of the DT will find different benefits for each level within the DT concept (prototypes, instances, aggregates, and environments). The infrastructure constructor or the final infrastructure manager must be considered to ensure the adequate level for the DT implementation. In this respect, each infrastructure has its own management needs, and not all of them demand IA or IoT for their daily usage. For instance, real time data of internal displacements are more important in tunnels than in conventional buildings. In this sense, the design and implementation of the DT must consider those differences. Considering different levels of a DT, Figure 1 details the information flow inside a complete digital environment. As detailed in previous DT definitions, basics levels could include (1) 3D representation, (2) data hosting, (3) real time information, and (4) predictive maintenance. It is important to highlight that the higher the DT implementation, the more technologies will be needed to achieve it. As shown in Figure 1, and considering most authors definitions of a DT, the base of the concept is a three-dimensional representation of the main geometric properties of the infrastructure; however, geometry visualisation is not a compulsory needed to create a DT. The most common technologies or methodologies used to archive geometry visualisation and initial data hosting are BIM and geographical information systems (GIS), but other technologies can be used depending on the nature of the infrastructure. While BIM is focused more on medium-small infrastructure, GIS has important benefits for bigger construction assets, such as roads, or to consider districts. Different construction assets will require different levels of detail. For example, bridges with large spans may need the use of 3D models, other bridges with modest distances among peers could be easily monitored only with a certain number of sensors. In any case, a different data nature could be implemented in a DT. Examples include geometric properties, like length or height, and physical properties of the materials, like density or compressive strength. Of course, this DT must be able to link any available information, providing quantity take-offs or cost estimations. However, data related to a DT should be divided into two types: the static (i.e., identification of a room or material) and the variable (owner of one locker or number of persons inside a one room). In this respect, to achieve an efficient DT implementation, data hosting must be designed as static data in the DT 3D representation and hosting dynamic data in external databases. In this sense, the system will be able to deal with several technologies, like IoT or AI, overpassing the lack of interoperability of the most important 3D representation systems.