## 7 Critical Conclusions and Future Work  
Certainly, harmonising the rules for defining the geometric and semantic contents of the 3D models of built environments is one of the most relevant challenges facing the framework of spatial and urban information management. When these purposes assert themselves in complex cultural and historical heritage domains, which involves considering parts of knowledge that is reciprocally related, the issue becomes more complex and an interdisciplinary approach is highly recommended. The workflow experimented with and presented in this paper shows that the direction is valid for a particular historical heritage  
sample, such as castles and towers. Moreover, the methodology can be extended to many other morphological featured domains by experimenting with proper rules of semantic segmentation.  
The designed ontology incorporates concepts and relations from different ontologies and vocabularies that express different interacting views in the historical built heritage (HBH) domain. Semantic information derived from the various case studies was also used to enrich the knowledge related to fortified structures. Since the field of study is vast, such an ontology could be further used to define relations among semantic information and spatial 3D models (Figure 13).  
On the other hand, by adopting the ontology-based approach or defining high-level ontological schemes, specific domain knowledge reuse will increase. The short-term perspective that seems most suitable is critically reviewing the structuring of HBIM models, designed according to current canons, and implementing it with the new classes, entities and relations expressed by the outlined ontology (Figure 14).  
Figure 14: Historical building information model (HBIM) geometric modelling phases of the Castellina (**A**) First HBIM modelling of conceptual mass families (from point cloud) identifying towers, building wings and courtyards. (**B**) HBIM model with walls and roofs. (**C**) Final HBIM model superimposed to the coloured cloud.  
Figure 13: Identifying architectural elements based on the CAD-like segmentation results and a topological analysis.  
Finally, another future development could regard the BIM-GIS (Geographic Information Science) harmonisation by checking the geometry, data formats and attribute integrations through the insertion of the 3D model in an ontology-based GIS environment [44].  
Conceptualisation, A.S., E.C., M.K., X.X.; methodology, A.S., E.C., M.K. and X.X.; software, X.X. and E.C.; validation, A.S., E.C., M.K., X.X., M.A.M. and F.N.; formal analysis, A.S., E.C., M.K., X.X.; investigation, A.S., E.C., M.K., X.X., M.A.M. and F.N.; resources, A.S. and X.X.; data curation, A.S., E.C., X.X. and M.K.; writing--original draft preparation, A.S., E.C., M.K., X.X.; writing--review and editing, A.S., E.C., M.K., X.X., M.A.M. and F.N.; visualisation, A.S., X.X. and E.C.; supervision, A.S., M.K. and M.A.M. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.