Principles and characteristics of CAD geometric modelling of historical buildings = Principios y características de los modelos geométricos CAD en edificios históricos

The first and unavoidable phase in the intervention in the Heritage and the existing building is the realization of a survey. Currently, its purpose is to build a digital geometric model in a computer system that serves to represent the built object and also serve as a geometric basis for further analysis. This paper takes a tour of the models used in building the survey data and what input and output information they use. These models are reduced to point clouds, wired-frame and curves and surfaces models. Solid modelling (BIM) is not widespread in this field given the difficulties presented by its application. All of them have in common that they codify by means of a database that includes the points of the survey and in some occasions another additional database is necessary to complete the reconstruction of the f the geometric information. This information management allows the development of computer applications that automatically analyse existing constructions based on geometry, such as the verification of the equilibrium of masonry structures. This work allows, therefore, clarifying the field that connects the geometric modelling, analytical representation and computational techniques with the architectural survey and intervention in Heritage.