dr.ir. Dennie Reniers

From 2005 to February 2009, I was a member of the Visualization Group of professor Jack van Wijk at the Eindhoven University of Technology. I obtained my PhD degree on February 12, 2009 under the supervision of Alex Telea.

I am currently working at SolidSource, an Eindhoven-based company providing solutions for software maintenance and management.

E-mail: . This address will stop functioning somwhere in 2009, try my gmail address instead (replace tue.nl by gmail.com).

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PhD thesis

Skeletons are shape descriptors that are of a lower dimensionality than the shape they describe. They are centered within the shape and capture the topology and articulation of the shape in a compact manner. These qualities make skeletonization a desirable pre-processing step in a variety of applications. In my dissertation, I present new techniques for computing multiscale skeletons of binary voxel shapes. Additionally, new shape segmentation methods are presented that benefit from the desirable properties of these skeletons.

Part-type segmentation using the Junction Rule (June 2008)

We present a part-type segmentation method for articulated voxel-shapes based on curve skeletons. Shapes are considered to consist of several simpler, intersecting shapes. Our method is based on the junction rule: the observation that two intersecting shapes generate an additional junction in their joined curve-skeleton near the place of intersection. For each curve-skeleton point, we construct a piecewise-geodesic loop on the shape surface. Starting from the junctions, we search along the curve skeleton for points whose associated loops make for suitable part cuts. The segmentations are robust to noise and discretization artifacts, because the curve skeletonization incorporates a single user-parameter to filter spurious curve-skeleton branches. Furthermore, segment borders are smooth and minimally twisting by construction. We demonstrate our method on several real-world examples and compare it to existing part-type segmentation methods.

Part-type segmentation using the Junction Rule (June 2008)

We present a new method for decomposing a 3D voxel shape into disjoint patch-type segments using the shape's simplified surface skeleton, and inspired by the symmetry-curvature duality. The surface skeleton of a shape consists of 2D manifolds inside its volume. Each skeleton point has a maximally inscribed ball that touches the boundary in at least two contact points. A key observation is that the boundaries of the simplified fore- and background skeletons map one-to-one to increasingly fuzzy, soft convex, respectively concave, edges of the shape. Using this property, we build a method for segmentation of 3D shapes which has several desirable properties. Our method segments both noisy shapes and shapes with soft edges which vanish over low-curvature regions. Multiscale segmentations can be obtained by varying the simplification level of the skeleton. We present a voxel-based implementation of our approach and illustrate it on several realistic examples.

Segmenting Simplified Surface Skeletons (September 2007)

A novel method for segmenting simplified skeletons of 3D shapes is presented. The so-called simplified Y-network is computed, defining boundaries between 2D sheets of the simplified 3D skeleton, which we take as our skeleton segments. We compute the simplified Y-network using a robust importance measure which has been proved useful for simplifying complex 3D skeleton manifolds. We present a voxel-based algorithm and show results on complex real-world objects, including very noisy ones.

Skeleton-based Hierarchical Shape Segmentation (March 2007)

We present an effective framework for part-type segmentation of 3D shapes using the curve skeleton. The junctions of the curve skeleton are detected to construct a partitioning of the object surface using geodesics. Because it is based on the curve skeleton, our segmentation intrinsically reflects the shape symmetry, topology, and articulation. By using geodesics we obtain segments that have smooth, minimally twisting borders. We describe a voxel-based implementation of our method which is robust, noise resistant, and which delivers level-of-detail segmentations.

Multiscale Curve and Surface Skeletons Using a Global Importance Measure (October 2006)

We present a novel approach for computing robust, multiscale curve and surface skeletons of 3D objects, using a global importance measure. The importance measure has an intuitive physical meaning, treating the curve and surface skeleton uniformly. Simply thresholding this measure delivers simplified skeletons at the desired scale which are connected by default due to the global nature of the measure.

Tolerance-based Feature Transforms (Februari 2006)

Tolerance-based feature transforms (TFTs) assign to each pixel in an image not only the nearest feature pixels on the object boundary, but all pixels from the minimum distance up to a user-defined tolerance. TFTs can for example be used to solve discretization problems in skeletonization. We compare four TFT algorithms on speed and accuracy. Our analysis is aimed at helping practitioners in the field to choose the right method for given accuracy and performance constraints.

Extreme simplification and rendering of point sets

In my Master's thesis I presented a novel approach for extreme simplification of point set models in the context of real-time rendering. Instead of simple point primitives, which are usually used for point-based rendering, a new primitive is proposed that has a larger approximation power and is essentially a multiscale generalization of point primitives. My supervisor during this project was Alexandru Telea.