A photogrammetric survey using knowledge representation on the arpenteur web-based photogrammetric workstation

ARPENTEUR is an application for digital photogrammetry mainly dedicated to architecture (Architectural PhotogrammEtry Network Tool for EdUcation and Research). One can freely access ARPENTEUR via the internet (http://moma.gamsau.archi.fr or http://photogeo.u-strasbg.fr). Usual steps of inner and outer orientation are implemented in order to generate a photogrammetric stereomodel. ARPENTEUR has been developed thanks to the collaboration of two complementary research laboratories : the group “Photogrammetry and Geomatics” of ENSAIS-LERGEC's laboratory (Strasbourg, France) and the Gamsau-MAP CNRS laboratory (CNRS : French National Body for Scientific Research) located in school of Architecture (Marseilles, France). This paper focuses on a new approach of photogrammetric surveying in which formalised architectural knowledge is a prerequisite to the measurement process. The first step of the survey is therefore a rigorous analysis of the architectural corpus used in the building. All the architectural elements which are expected to be measured are defined and organised in a hierarchy of concepts and formalised using the Java™ object language capabilities. The purpose of the photogrammetric measurement is then to inform the architectural geometrical model with data such as location, orientation and dimension. Each architectural element considered is given within its definition a redundant set of geometrical primitives that can be observed on its surface. These primitives appear as a geometrical interpretation of the architectural element's morphology. Depending on the case study's specificity, one can choose to measure a subset of these primitives. Unmeasured data (occulted zone on a picture, ... ) should be generated by the system using both theoretical model and measured data. We propose an experimentation of this process on the old town hall tower, in Krakow (Poland). Images used in the system were taken with a point and shoot digital camera. The experimentation focuses the neo-gothic addition to the original XIVth century tower. Elements considered therefore correspond to a reconstruction based on a historical analysis of Krakow's gothic urban corpus. The model resulting from the survey process can be visualised either on the internet-oriented VRML plug-ins, or inside the Microstation™ software.