## 4 Method
### Model Generation and Information Mapping
An earlier version of the rib vault was used in the 8 th century in Islamic Architecture at the Mosque-Cathedral of Cordoba in Moorish Spain. However, it was decorative, not bearing the structure's weight. They were also frequently used in later Romanesque and Norman architecture. Beginning in the 11 th century, they were used in all of the major Gothic Catherals in Europe. Their form gradually changed from a complex sexpartite vault to a simpler but stronger quadripartite vault, allowing much higher cathedrals. By the 13 th century, they had again become highly ornamental and complex. The sexpartite vault appeared simultaneously in France and England. The first cathedral to use sexpartite vaults was Durham Cathedral, which begun in 1093. Durham was initially intended to be built with more traditional groin vaults. Early examples of sexpartite rib vaults are found at the Abbaye-aux-Hommes (begin 1066) and Abbaye-aux-Dames at Caen. It then appeared in Noyon Cathedral (begin 1131); the square Gothic porch of the Romanesque Church of Vezelay Abbey in France (1132); Sens Cathedral (begin 1135); the choir of the Abbey of Saint-Denis (begin 1140); Notre-Dame de Paris (begin 1163); Bourges Cathedral; Laon Cathedral. Finally, ribbed vaults were built by [PERSON] at Canterbury Cathedral and in St Faith's Chapel in Westminster Abbey (1180). In the vaulted system of San Valentino church, each bay is composed of stone ribs into multiple compartments. The ribs diagonally crossing the structure formed a pointed arch, and there is an intermediate pointed arch, which crossed from side to side. Since the ribs carried the vault's weight, the panels are made of small pieces of stone and were much lighter than traditional vaults (barrel, groin, etc.). The ribs transmitted the weight downwards and outwards through columns to the piers on the lower level and additional weight of the diagonal traverse arches is supported by massive piers. Since the weight of the vaults is carried by the columns and piers, not the walls, the walls could be higher, and they are filled with more oversized stained glass windows. Consequently, it is immediate to understand how the geometric complexity of these two structural elements required a scan-to-BIM process capable of respecting the geometric complexity of the elements but at the same time allowed to maintain both high degrees of accuracy (GOA) and levels of detail (LOD) is a sustainable generative process and not too expensive in terms of time and costs related to the modelling itself. For these reasons, the generative method has provided for applying the scan-to-BIM requirements of both GOGs. Following the first phase of identifying the points that define both vaults, the geometric edges of the various components of the vaults were intercepted through automatic extraction and manual 3D drawing. Geometric discretion, at the heart of the scan-to-BIM process and the application of GOG 9 and GOG 10, has made it possible to appropriately identify geometric primitives capable of accurately representing elements such as:  
* wedge-shaped pieces called voussoirs which are held in place by the pressure of the neighbouring pieces;
* abutments: a structure to support the lateral pressure of an arch or span;
* imposts: top course of a pillar or a wall that supports the arch;
* intrados: inner curve and surface of an arch or vault;
* estrados: determination of the wall thickness of the vault (through the GOG 10, it is possible to hypothesise the thickness parameter and update it according to subsequent inquiries);* keystones: the intersection of the ribs of a rib vault. It is structurally important since it marks the apex of the vault;
* diagonal ribs: diagonal elements between two walls to divide a vault into bays. An arch of masonry, often moulded, forms part of the framework on which a vault rests. Ribs generally project from the undersurface of the vault.