Completing Digital Cultural Heritage Objects by Sketching Subdivision Surfaces toward Restoration Planning Matthias Bein 1 , Sebastian Peña Serna 2 , André Stork 1,2 , Dieter W. Fellner 1,2 1 GRIS - Graphisch Interaktive Systeme, Technische Universität Darmstadt, Fraunhoferstrasse 5, D-64283 Darmstadt, Germany 2 Fraunhofer IGD, Fraunhoferstrasse 5, D-64283 Darmstadt, Germany Matthias.Bein@gris.informatik.tu-darmstadt.de Sebastian.Pena.Serna@igd.fraunhofer.de Andre.Stork@igd.fraunhofer.de Dieter.Fellner@igd.fraunhofer.de Abstract. In the restoration planning process a curator evaluates the condition of a Cultural Heritage (CH) object and accordingly develops a set of hypotheses for improving it. This iterative process is complex, time consuming and requires many manual interventions. In this context, we propose interactive modeling techniques, based on subdivision surfaces, which can support the completion of CH objects toward restoration planning. The proposed technique starts with a scanned and incomplete object, represented by a triangle mesh, from which a subdivision surfaces can be generated. Based on the mixed representation, sketching techniques and modeling operations can be combined to extend and refine the subdivision surface, according to the curator’s hypothesis. Thus, curators without rigorous modeling experience can directly create and manipulate surfaces in a similar way as they would do it on a piece of paper. We present the capabilities of the proposed technique on two interesting CH objects. Keywords: Sketching, Subdivision, Modeling, Restoration Planning, Hypothesis 1 Introduction The preservation and conservation of Cultural Heritage (CH) objects is one of the most important objectives of any Cultural Heritage institution. This objective is associated with many activities, ranging from storage to exhibition, passing over the conduction of restoration works. In the context of restoration, the restorer deals with the examination of CH objects, in order to evaluate the condition of the object and the need of a restoration work. If a restoration work needs to be conducted, the restorer