Gerhard H. Bendels

Image-based registration of 3D-range data using feature surface elements

Digitizing real-life objects via range scanners, stereo vision or tactile sensors usually requires the composition of multiple range images. In this paper we exploit intensity images often recorded with the range data and propose a fully automatic registration technique using 2D-image features with intrinsic scale information for finding corresponding points on the 3D-views. In our approach, the fine registration of two range images is performed by first aligning the feature points themselves, followed by a so-called constrained-domain alignment step. In the latter, rather than feature points, we consider feature surface elements that are derived using the scale information inherently established with the 2D-features. The global registration error is minimized using graph relaxation techniques to mediate the transformations required to align the multiple range images. We demonstrate the power and feasibility of our method by a case-study in the cultural heritage domain.

Mesh forging: editing of 3D-meshes using implicitly defined occluders

In recent years the ease of use and the flexibility in the editing process shifted into focus in modelling and animation applications. In this spirit we present a 3D mesh editing method that is similar to the simple constrained deformation (scodef) method9. We extend this method to the so-called mesh forging paradigm by adding an occluder to the editing environment. Our method resembles and was in fact motivated by the forging process where an anvil is used to give the manipulated object the desired shape. While users perform the editing operation by directly manipulating the 3D-mesh, the occluder is defined implicitly. To enable fine detail edits even in sparsely triangulated areas, we propose an adaptive refinement method that also allows the creation of sharp features where desired. The functionality and ease of use of our editing approach is shown by several examples.

Rapid synchronous acquisition of geometry and appearance of cultural heritage artefacts

In order to produce visually appealing digital models of cultural heritage artefacts, a meticulous reconstruction of the 3D geometry alone is often not sufficient, as colour and reflectance information give essential clues of the objects material. Standard texturing methods are often only able to overcome this fact under strict material and lighting condition limitations. The realistic reconstruction of complex yet frequently encountered materials such as fabric, leather, wood or metal is still a challenge. In this paper, we describe a novel system to acquire the 3Dgeometry of an object using its visual hull, recorded in multiple 2D images with a multi-camera array. At the same time, the material properties of the object are measured into Bidirectional Texture Functions (BTF), that faithfully capture the mesostructure of the surface and reconstruct the look-and-feel of its material. The high rendering fidelity of the acquired BTF texture data with respect to reflectance and self-shadowing also alleviates the limited precision of the visual hull approach for 3D geometry acquisition.

Detail-preserving surface inpainting

Inpainting is a well-known technique in the context of image and art restoration, where paint losses are filled up to the level of the surrounding paint and then coloured to match. Analogue tasks can be found in 3D geometry processing, as digital representations of real-world objects often contain holes, due to hindrances during data acquisition or as a consequence of interactive modelling operations. In this paper we present a novel approach to automatically fill-in holes in structured surfaces where smooth hole filling is not sufficient. Previous approaches inspired by texture synthesis algorithms require specific spatial structures to identify holes and possible candidate fragments to be copied to defective regions. Consequently, the results depend heavily on the choice and location of these auxiliary structures, such that for instance symmetries are not reconstructed faithfully. In contrast, our approach is based on local neighbourhoods and therefore insensitive with respect to similarity transformations. We use so-called guidance surfaces to guide and prioritise the atomic filling operations, such that even non-trivial and larger holes can be filled consistently. The guidance surfaces are automatically computed and iteratively updated during the filling process, but can also incorporate any additional information about the surface, if available.

Free-form modelling for surface inpainting

In this paper, we describe a novel approach to 3D shape modelling, targeting at the reconstruction and repair of digitised models -- a task that is frequently encountered in particular in the fields of cultural heritage and archaeology. In these fields, faithfully digitised models are often to be restorated in order to visualise the object in its original state, reversing the effects of aging or decay. In our approach, we combine intuitive free-form modelling techniques with automatic 3D surface completion to derive a powerful modelling methodology that on the one hand is capable of including a users expertise into the surface completion process. The automatic completion, on the other hand, reconstructs the required surface detail in the modelled region and thus frees the user from the need to model every last detail manually. The power and feasibility of our approach is demonstrated with several examples.

Towards the next generation of 3D content creation

In this paper we present a novel integrated 3D editing environment that combines recent advantages in various fields of computer graphics, such as shape modelling, video-based Human Computer Interaction, force feedback and VR fine-manipulation techniques. This integration allows us to create a new compelling form of 3D object creation and manipulation preserving the metaphors designers, artists and painters have accustomed to during their day to day practice. Our system comprises a novel augmented reality workbench and enables users to simultaneously perform natural fine pose determination of the edited object with one hand and model or paint the object with the other hand. The hardware setup features a non-intrusive, video-based hand tracking subsystem, see-through glasses and a 3D 6-degree of freedom input device. The possibilities delivered by our AR workbench enable us to implement traditional and recent editing metaphors in an immersive and fully three-dimensional environment, as well as to develop novel approaches to 3D object interaction.