# GIS and BIM as Integrated Digital Environments for Modeling and Monitoring of Historic Buildings
## 1 Introduction
The Building Information Modeling (BIM) platform was initially developed for the representation and management of new structures and not for an existing one [27; 28]. Therefore, in the cases of documenting an existing structure through BIM, architectural and/or geometric data are required. Furthermore, semantic information, is developed through parametric object libraries in the case of new structures [27; 28; 29; 30; 31] while for existing buildings, modifications are expected [32; 33]. In this framework, that is for existing buildings, the elaboration of a 3D model deriving from LS and image-based techniques into BIM is a task that is both time-consuming and complex; since this process includes high amount of data of high resolution and often involves 3D products that represent elements of high complexity. In the field of BIM research there is a number of efforts, attempting to solve these issues in an automatic manner, since automation may greatly diminish cost and decisively minimize time consuming surveys [34; 35; 36]. In addition, these efforts can contribute in the fields of interoperability and multi-disciplinarily in both structural assessment and refurbishment projects. However, the issue concerning cultural heritage assets is of higher complexity in all the above and other relevant fields [32; 34; 36]. In heritage building information modeling (HBIM), besides historical data, building materials data are also required to fully comprehend the historical structure, especially since they may differ significantly from asset to asset. Therefore, the parametric objects of an HBIM can be modified and updated including building materials information to depict the current state of preservation of a monument. Regarding the preservation state assessment of a monument in HBIM, some attempts have been made by the scientific community; however, this issue is still challenging [37; 38; 39; 40; 41; 42]. The most important issue is related to the fact that an expert not only needs to obtain all the relevant information, but most importantly has to elaborate this information within an ICT (information and communication technology) platform; resulting in an HBIM which is strongly dependent on the experts' experience and data accessibility [10; 18; 27; 32]. In this work, an approach regarding the representation of a monument's state of preservation, through GIS and BIM platform is presented, incorporating historical, architectural, surveying and building materials data. This is accomplished through the integration of data within 2D GIS thematic maps, as well as the development of a 3D HBIM. Therefore, all the above-mentioned multidisciplinary data are merged within both information systems, and valuable information regarding the assessment of the preservation state of a historic building is exported. The aim of this work is the creation of a BIM using both geometric and architectural documentation data. Furthermore, in the process of developing an HBIM, besides historical information, data of building materials characterization and decay diagnosis are added through the elaboration of the corresponding thematic maps in 2D GIS, enhancing, therefore, the interoperability of the presented model. In addition, emphasis is given to the structural degradation of the building, through the representation and the elaboration analysis of the cracks, which are formed as elements within the HBIM; thus, valuable information is exported regarding structural assessment and monitoring, as well as for other interoperable purposes. Consequently, preventive actions and conservation interventions can be planned to minimize the progress of degradation and subsequently the cost for future restoration; overall, the goal is to extend the monuments' lifetime, preserving built cultural heritage assets for future generations [17; 19].