A stone-by-stone photogrammetric survey using architectural knowledge formalised on the arpenteur photogrammetric workstation

Résumé 0

ARPENTEUR is a web application for digital photogrammetry mainly dedicated to architecture (ArchitecturalPhotogrammEtry Network Tool for EdUcation and Research) available at http ://www.arpenteur.net. ARPENTEUR hasbeen developed by two complementary research teams: the “Photogrammetry and Geomatics” group of ENSAIS-LERGEC's laboratory (Strasbourg, France) and the Gamsau-MAP CNRS laboratory located in the school ofArchitecture of Marseilles (France).This paper focuses on a new approach of stone-by-stone surveying in which formalised architectural knowledge is usedas a prerequisite to the photogrammetric measurement process.In addition to this morphological definition, the structure point of view is implemented in the model in order to considersome architectural elements as containing a set of ashlar blocks. In our approach of stone-by-stone surveying, which hasbeen conceived for the study of historical ashlar masonry but can be applied to other types of investigation, themeasurement is performed directly on each individual stone in its built context. A previous edifice analysis , conductedby an archaeologist, is necessary to define the construction characteristics and chronology, and the properties of all themeasured architectural entities. This results in the definition of an approximate depth for each type of stone, allowing alimited survey to the blocks visible part. An extrusion vector is computed in order to inform lacking geometricaldescription of the block.Once the instanced block is measured a polyhedron representation of its morphology is generated. The instance is alsoadded to a data structure in which it is positioned according to topological or geometrical order. The result is therefore acollection of ordered blocks that includes, for instance, for each block data on its neighbours (adjacent blocks). Whencompleted, the tool will create a direct link between the architectural object and the database, enabling to locate andthus identify the properties of each block registered in the database. The possibilities of this new type of approach toarchitecture extend from archaeology to restoration and maintenance to any type of structure treated byphotogrammetrical survey.Retrieving architectural information (for example the intrados radius of an arch) is the approach we have developed inarchitectural surveying. We are currently working on giving this possibility in the stone-by-stone surveying process onwhich this paper focuses.