Content-based Retrieval of 3D Models through Curvature Maps: A CBR Approach Exploiting Media Conversion

Multimedia digital libraries are gaining an increasing relevance, and are growing in both number and size. Moreover, advancements in acquisition and authoring technologies have also caused new media types to be added to these libraries. For instance, animations and 3D models have recently come alongside more traditional media such as text, images, audio and video. In particular, even if 3D objects were initially included in multimedia digital libraries in the form of images (i.e., views of the objects), they are now also available in the form of 3D models. These allow to overcome the inherent limitations of an image-based representation of a three-dimensional reality. In this paper we present a novel method for description and retrieval of 3D models that relies on curvature maps: after an initial pre-processing of the model, differential properties of points on the surface of the 3D object are evaluated; the model surface is then deformed into an ellipsoid, and is mapped onto a 2D image retaining curvature information of the original model. Through this media conversion from 3D model to image map, we enable application of analysis, description, and matching techniques which have been originally conceived for the image medium. In particular, the two approaches described in this paper rely on histograms for a coarse but efficient description of tiles of the curvature map, and on weighted walkthroughs for a more precise description of homogeneous regions of the map, taking into account their spatial arrangement and areas. Experimental results reveal that both techniques can be successfully applied to curvature maps. The two approaches have been compared against other solutions presented in literature, and have shown a good retrieval performance (particularly in the case of region-based description).