Patrick Reuter

GeoTUI: a tangible user interface for geoscience

GeoTUI is a system designed for geophysicists that provides props as tangible user interface on a tabletop vision-projection system for the selection of cutting planes on a geographical map of a subsoil model. Our GeoTUI system allows the geophysicists to manipulate in the same action and perception space since the movement of the physical artifacts is done on the tabletop and thus constrained to two dimensions. Consequently, it combines the advantages of the spontaneous conditions of user interaction that the geophysicists are commonly used to in their classical paper/pen/ruler environment with the advantages of the use of powerful geological simulation software. We conducted an extensive user study in the workplace of the geophysicists that clearly revealed that using a tangible interaction performs better than using the standard mouse/keyboard GUI for the cutting line selection task on a geographical subsoil map. Consequently, it increases the efficiency for the real-world trade task of hypothesis validation on a subsoil model. Moreover, this geological user case is complex enough to confirm the hypothesis that in space-multiplex conditions, specialized devices perform better than generic ones.

Point-based modelling and rendering using radial basis functions

A point-based 3D surface modelling technique combined with a new point rendering technique is presented. Surfaces are modelled by specifying a set of unorganized points on the surface. An implicit representation of the surface through these points minimizing the bending energy is then calculated using radial basis functions while guaranteeing a specifiable continuity. The surface is directly rendered view-dependently in an output-sensitive multiresolution manner without the creation of a polygonal mesh representation. This is done by the local generation of 3D surface points for the rendering adapted to the output device. A new texturing technique using the material properties of the points is presented.

The Revealing Flashlight: Interactive Spatial Augmented Reality for Detail Exploration of Cultural Heritage Artifacts

Cultural heritage artifacts often contain details that are difficult to distinguish due to aging effects such as erosion. We propose the revealing flashlight, a new interaction and visualization technique in spatial augmented reality that helps to reveal the detail of such artifacts. We locally and interactively augment a physical artifact by projecting an expressive 3D visualization that highlights its features, based on an analysis of its previously acquired geometry at multiple scales. Our novel interaction technique simulates and improves the behavior of a flashlight: according to 6-degree-of-freedom input, we adjust the numerous parameters involved in the expressive visualization—in addition to specifying the location to be augmented. This makes advanced 3D analysis accessible to the greater public with an everyday gesture, by naturally combining the inspection of the real object and the virtual object in a colocated interaction and visualization space. The revealing flashlight can be used by archeologists, for example, to help decipher inscriptions in eroded stones, or by museums to let visitors interactively discover the geometric details and meta-information of cultural artifacts. We confirm its effectiveness, ease of use, and ease of learning in an initial preliminary user study and by the feedback of two public exhibitions.

Surface reconstruction with enriched reproducing kernel particle approximation

There are many techniques that reconstruct continuous 3D surfaces from scattered point data coming from laser range scanners. One of the most commonly used representations are point set surfaces (PSS) defined as the set of stationary points of a moving least squares (MLS) projection operator. One interesting property of the MLS projection is to automatically filter out high frequency noise, that is usually present in raw data due to scanning errors. Unfortunately, the MLS projection also smoothes out any high frequency feature, such as creases or corners, that may be present in the scanned geometry, and does not offer any possibility to distinguish between such feature and noise. The main contribution of this paper, is to present an alternative projection operator for surface reconstruction, based on the enriched reproducing kernel particle approximation (ERKPA), which allows the reconstruction process to account for high frequency features, by letting the user explicitly tag the corresponding areas of the scanned geometry.

Reconstructing multi-scale variational partition of unity implicit surfaces with attributes

Real-world 3D models are primarily acquired as large unorganized discrete point sets with attributes. In this paper, we show how to reconstruct multi-scale implicit surfaces with attributes, given those discrete point sets with attributes. In a preprocess, we first subdivide the global domain into overlapping local subdomains by computing a perfectly balanced binary tree. Second, we compute subsets of the points for the inner nodes of the tree for the intermediate resolutions bottom-up by using data thinning algorithms. Third, we reconstruct the surface parts in all nodes of the binary tree from the non-disjunct subsets of the points by using variational techniques with radial basis functions. For the evaluation of the defining function of the implicit surface at the desired scale, we hierarchically blend together the surface parts of the inner nodes by using a family of functions called partition of unity. Our new reconstruction method is particularly robust since the number of data points in the partition of unity blending zones can be specified explicitly. We show how our reconstruction method can also be applied to reconstruct continuous functions for the surfaces attributes. In a short discussion, we evaluate the advantages and drawbacks of our reconstruction method compared to existing reconstruction methods for implicit surfaces.

Growing Least Squares for the Analysis of Manifolds in Scale-Space

We present a novel approach to the multi‐scale analysis of point‐sampled manifolds of co‐dimension 1. It is based on a variant of Moving Least Squares, whereby the evolution of a geometric descriptor at increasing scales is used to locate pertinent locations in scale‐space, hence the name “Growing Least Squares”. Compared to existing scale‐space analysis methods, our approach is the first to provide a continuous solution in space and scale dimensions, without requiring any parametrization, connectivity or uniform sampling. An important implication is that we identify multiple pertinent scales for any point on a manifold, a property that had not yet been demonstrated in the literature. In practice, our approach exhibits an improved robustness to change of input, and is easily implemented in a parallel fashion on the GPU. We compare our method to state‐of‐the‐art scale‐space analysis techniques and illustrate its practical relevance in a few application scenarios.

ArcheoTUI - a tangible user interface for the virtual reassembly of fractured archeological objects

Cultural objects of archeological findings are often broken and fractured into a large amount of fragments, and the archeologists are confronted by 3D puzzles when reassembling the fractured objects. Scanning the fragments and reassembling the corresponding 3D objects virtually is an elegant (and sometimes the only) solution. An efficient user interaction for the complex task to orientate or position two 3D objects relative to each other is essential, eventually in addition to automatic matching techniques. In this paper, we present ArcheoTUI, a new tangible user interface for the efficient assembly of the 3D scanned fragments of fractured archeological objects. The key idea is to use tangible props for the manipulation of the vir- tual fragments. In each hand, the user manipulates an electromagnetically tracked prop, and the translations and rotations are directly mapped to the corresponding virtual fragments on the display. For each hand, a correspond- ing foot pedal is used to clutch the movements of the hands. Hence, the hands of the user can be repositioned, or the user can be switched. The software of ArcheoTUI is designed to easily change assembly hypotheses, beyond classical undo/redo, by using a scene graph. We designed ArcheoTUI on the demand of archeaologists and in a direct collaboration with them, and we con- ducted a user study on site at their workplace. This user study revealed that the interface, and especially the foot pedal, was accepted, and that all the users managed to solve simple assembly tasks. In a case study, we show the assembly of one of their fractured archeological findings.

Semi-automatic geometry-driven reassembly of fractured archeological objects

3D laser scanning of broken cultural heritage content is becoming increasingly popular, resulting in large col- lections of detailed fractured archeological 3D objects that have to be reassembled virtually. In this paper, we present a new semi-automatic reassembly approach for pairwise matching of the fragments, that makes it possible to take into account both the archeologists expertise, as well as the power of automatic geometry-driven match- ing algorithms. Our semi-automatic reassembly approach is based on a real-time interaction loop: an expert user steadily specifies approximate initial relative positions and orientations between two fragments by means of a bimanual tangible user interface. These initial poses are continuously corrected and validated in real-time by an algorithm based on the Iterative Closest Point (ICP): the potential contact surface of the two fragments is identi- fied by efficiently pruning insignificant areas of a pair of two bounding sphere hierarchies, that is combined with a k-d tree for closest vertex queries. The locally optimal relative pose for the best match is robustly estimated by taking into account the distance of the closest vertices as well as their normals. We provide feedback to the user by a visual representation of the locally optimal best match and its associated error. Our first results on a concrete dataset show that our system is capable of assisting an expert user in real-time during the pairwise matching of downsampled 3D fragments.

ArcheoTUI—Driving virtual reassemblies with tangible 3D interaction

ArcheoTUI is a new tangible user interface for the efficient assembly of the 3D scanned fragments of fractured archeological objects. An efficient user interaction for the complex task to orientate or position two 3D objects relative to each other is essential, eventually in addition to automatic matching techniques. Our key idea is to use tangible props for the manipulation of the virtual fragments. In each hand, the user manipulates an electromagnetically tracked prop, and the translations and rotations are directly mapped to the corresponding virtual fragments on the display. For each hand, a corresponding foot pedal is used to clutch the movements of the hands. Hence, the users hands can be repositioned, or the user can be switched. The software of ArcheoTUI is designed to easily change assembly hypotheses, beyond classical undo/redo, by using a scene graph. We designed ArcheoTUI on the demand of archeaologists and in a direct collaboration with them, and we conducted two user studies on site at their workplace. The first user study revealed that the interface, and especially the foot pedal, was accepted, and that all the users managed to solve simple assembly tasks. In a second user study, we compare a different clutching mechanism with buttons on the props to the foot pedal mechanism. This second user study revealed that the movement of the hands is more similar to real-world assembly scenarios when using the foot pedals, and that the users can keep on concentrating on the actual assembly task. Finally, we show how the virtual assembly is used for a fractured archeological finding.

Surfel Stripping

This paper presents an efficient combination of techniques for fast stripping and multiresolution rendering of Point-Based Surfaces (PBS) called Surfel Stripping. Surfel Strips are small triangle strips that interpolate the PBS. There are two major contributions. First, at loading time, we efficiently convert the PBS into triangle strips. This is done by first generating a set of overlapping small triangular meshes that interpolate the PBS, then removing redundant triangles and finally stripping the small triangular meshes by using a cache-friendly stripping method. All these operations are performed by using an octree data structure. Second, we reuse this data structure for providing a multiresolution interactive visualization of the surfel strips at rendering time. Since Surfel Stripping is local and very fast, it can be used in a lot of situations as an object-space alternative to the image-space surface splatting and thus be considered half way between point-based rendering and local polygonal generation. Rendering Surfel Strips is very efficient since it neither requires multi-pass rendering nor time-consuming vertex/fragment shaders compared to surface splatting. We show also how to exploit the locality of the surfel strips for maintaining compatibility with point-based modeling tools, such as local deformations of surfaces. We finally give some examples of well known visual enrichments developed for polygons, directly applied to PBS thanks to surfel strips.