Digital valorising of historical scale models of cities for adaptative and innovative uses – Urbania

The collection of plans-reliefs is an exceptional legacy that includes a hundred 1:600-scale models, measuring over several dozen square meters. These models of the strongholds that marked the French borders are now the witnesses of the formation of the territory. They are characterized by a unique power of seduction and evocation, but the plans-reliefs are also emblematic of a national and local collective memory. Even if successful events foreground rarely exposed scale models, the collection is a victim of its size and fragility. The plans-reliefs are confronted with the question of how to preserve, valorize and disseminate a witness of French history, of its borders, cities and countryside. These last years, many projects dealing with historical scale models digitizing have been conducted. Most of them only aim at the visualizing of simple 3D textured model which lack semantic enhancement. The goal of URBANIA is to facilitate the knowledge and the access of this cultural heritage to a wider and more varied public. It can be achieved by generating contents, innovative services and perennial conservation. The virtual model is not intended to replace the scale model: it sets up a dialogue with other resources or other virtual plans-reliefs. The project aims at centralize, enhance, harmonize and analyze data specific to urban scale models (history and manufacturing techniques, evolution of territory representation methods, etc.). The produced data have to clarify the context of establishment of the scale models, of the representation of the French territory and its diversity at the time of the making of the collection (from the point of architecture, urbanism, landscape and historic texts, archives, etc.). To establish a digital continuum (from acquisition to reconstruction) for the exploitation of virtual scale models of cities, it is necessary to treat the geometric data from the survey. The aim is the creation of a geometric model which is relevant and semantic. Only then will the model be able to be exploited within a web information system (2D/3D data bases, multi-representation, multi-scale, etc.). Thus, reality based modeling is the focal point of several technologic barriers. In the fields of digital valorizing for cultural heritage, the making of 3D models is based on 3D survey techniques. Quick automatic and cheap tools allow accurate 3D digitizing of objects of all shapes and sizes. However, geometric, material, environment and economic factors generate approximations in the 3D survey of plans-reliefs. The digitizing pipeline requires further treatments to remove these barriers and to create semantic 3D documents. The extraction of key features from point cloud and the automatic reconstruction of architectural objects will enhance representation giving more meaning. The representation becomes the 3D interface of an GIS dedicated to the knowledge of the plan-relief of Strasbourg, and by extension to the knowledge of the whole collection. The data model allows the adaptation of the content according to scenarios and users because the information can be filtered. Our proposal is made in the context of several scientific domains such as semantic segmentation of 3D surveys, parametric modeling, semantic characterization of architectural shapes and 3D GIS applied to information model processing.