Lasergrammetry and high precision topography measurements to study a complex fortified building: Tour de la Pelote (Besançon, France)

As part of its Heritage Atlas project, the municipality of Besancon in partnership with MSHE C.N. Ledoux from the University of Franche- Comte, started a 3D data acquisition focused on a military building, the Tour de la Pelote. This late Middle Ages tower, subsequently included in Vauban's fortified architectural program (UNESCO world heritage) at the end of the seventeenth century, was ravaged by fire in 2013. An archaeological survey was then carried out to investigate the building evolution, prior to its complete restoration in accordance with the past construction. Despite great investment, the tower, remains inaccessible because of security issues.In order to ensure both general public access and research activities on this complex type of archaeological building, it was decided by the partners to acquire high resolution measurement series using a Riegl VZ400 T-Lidar Scanner. The inherent architectural complexity of the building, tied to narrow and steep stairs connections between each floor and a demanding surrounding, remains a challenge not reachable with conventional approaches. This presentation will focus on how to overcome those issues with acquisition methods developed by integrating 3D laser data and high precision topographic data (millimeter scale) indoor and outdoor. Measurements quality and RMS errors will be discussed in order to observe the correlation between various phases of constructions and restorations more or less documented in previous archeological data. With the Tour de la Pelote example, we intend to show how an heritage project designed for public mediation can also contribute to interdisciplinary research.