Berner, Alexander

Dr. Alexander Berner-Gandras

( Alexander Berner )

Email: At Uni Bonn


I moved...



Research Interests



Publications


Animation Cartography - Intrinsic Reconstruction of Shape and Motion

Animation Cartography - Intrinsic Reconstruction of Shape and Motion
A. Tevs, A. Berner, M. Wand, I. Ihrke, M. Bokeloh, J. Kerber, H.-P. Seidel,
In: ACM Transactions on Graphics, 31(2), April 2012.
Presented at SIGGRAPH 2012, Los Angeles, USA

paper (preprint, PDF, 10MB)
video (mp4, 290 MB)

Abstract
In this paper, we consider the problem of animation reconstruction, i.e., the reconstruction of shape and motion of a deformable object from dynamic 3D scanner data, without using user provided template models. Unlike previous work that addressed this problem, we do not rely on locally convergent optimization but present a system that can handle fast motion, temporally disrupted input, and can correctly match objects that disappear for extended time periods in acquisition holes due to occlusion. Our approach is motivated by cartography: We first estimate a few landmark correspondences, which are extended to a dense matching and then used to reconstruct geometry and motion...

A Morphable Part Model for Shape Manipulation

A Morphable Part Model for Shape Manipulation
Alexander Berner, Oliver Burghard, Michael Wand, Niloy J. Mitra, Reinhard Klein, Hans-Peter Seidel,
MPI Informatik Tech Report MPI-I-2011-4-005, December 2011

Abstract
We introduce morphable part models for smart shape manipulation using an assembly of deformable parts with appropriate boundary conditions. In an analysis phase, we characterize the continuous allowable variations both for the individual parts and their interconnections using Gaussian shape models with low rank covariance. The discrete aspect of how parts can be assembled is captured using a shape grammar. The parts and their interconnection rules are learned semi-automatically from symmetries within a single object or from semantically corresponding parts across a larger set of example models. The learned discrete and continuous structure is encoded as a graph. In the interaction phase, we obtain an interactive yet intuitive shape deformation framework producing realistic deformations on classes of objects that are difficult to edit using existing structure-aware deformation techniques. Unlike previous techniques, our method uses self-similarities from a single model as training input and allows the user to reassemble the identified parts in new configurations, thus exploiting both the discrete and continuous learned variations while ensuring appropriate boundary conditions across part boundaries.

Shape Analysis with Subspace Symmetries

Shape Analysis with Subspace Symmetries
Alexander Berner, Michael Wand, Niloy J. Mitra, Daniel Mewes, Hans-Peter Seidel, Computer Graphics Forum (Proceedings of Eurographics 2011).
Project Page (Paper, Slides and Video)

Abstract
We address the problem of partial symmetry detection, i.e., the identification of building blocks a complex shape is composed of. Previous techniques identify parts that relate to each other by simple rigid mappings, similarity transforms, or, more recently, intrinsic isometries. Our approach generalizes the notion of partial symmetries to more general deformations. We introduce subspace symmetries whereby we characterize similarity by requiring the set of symmetric parts to form a low dimensional shape space. We present an algorithm to discover subspace symmetries based on detecting linearly correlated correspondences among graphs of invariant features. The detected subspace symmetries along with the modeled variations are useful for a variety of applications including ...

Intrinsic Shape Matching by Planned Landmark Sampling

Intrinsic Shape Matching by Planned Landmark Sampling
A. Tevs, A. Berner, M. Wand, I. Ihrke, H.-P. Seidel, Computer Graphics Forum (Proceedings of Eurographics 2011).
paper pdf (18 MB)
Project Page

Abstract
Recently, the problem of intrinsic shape matching has received a lot of attention. A number of algorithms have been proposed, among which random-sampling-based techniques have been particularly successful due to their generality and efficiency. We introduce a new sampling-based shape matching algorithm that uses a planning step to find optimized ”landmark” points. These points are matched first in order to maximize the information gained and thus minimize the sampling costs. Our approach makes three main contributions: First, the new technique leads to a significant improvement in performance, which we demonstrate on a number of benchmark scenarios. Second, our technique does not require any keypoint detection ...

Generalized Intrinsic Symmetry Detection

Generalized Intrinsic Symmetry Detection
A. Berner, M. Bokeloh, M. Wand, A. Schilling, , H.-P. Seidel,
MPI Informatik Tech Report MPI-I-2009-4-005, August 2009
paper pdf (6 MB)

Abstract
In this paper, we address the problem of detecting partial symmetries in 3D objects. In contrast to previous work, our algorithm is able to match deformed symmetric parts: We first develop an algorithm for the case of approximately isometric deformations, based on matching graphs of surface feature lines that are annotated with intrinsic geometric properties. The sensitivity to non-isometry is controlled by tolerance parameters for each such annotation. Using large tolerance values for some of these annotations and a robust matching of the graph topology yields a more general symmetry detection algorithm that can detect similarities in structures that have undergone strong deformations. This approach for the first time allows for detecting partial intrinsic as well as more general, non-isometric symmetries...

Symmetry Detection Using Line Features

Symmetry Detection Using Line Features
M. Bokeloh, A. Berner, M. Wand, H.-P. Seidel, A. Schilling, Computer Graphics Forum (Proceedings of Eurographics) 2009
Project Page (Paper and Videos)

Selected as cover image of Informatik-Spektrum 32(2), Springer-Verlag, April 2009

Abstract
In this paper, we describe a new algorithm for detecting structural redundancy in geometric data sets. Our algorithm computes rigid symmetries, i.e., subsets of a surface model that recur several times within the model differing only by translation, rotation or mirroring. Our algorithm is based on matching locally coherent constellations of feature lines on the object surfaces. In comparison to previous work, the new algorithm is able to detect a large number of symmetric parts without restrictions to regular patterns or nested hierarchies....

Symmetry Detection Using Line Features

Efficient Reconstruction of Non-rigid Shape and Motion from Real-Time 3D Scanner Data
M. Wand, B. Adams, M. Ovsjanikov, A. Berner, M. Bokeloh, P. Jenke, L. Guibas, H.-P. Seidel, A. Schilling, ACM Transactions on Graphics (TOG) Volume 28(2), April 2009
Paper (Technical Report Version, WSI-2009-01) - video: avi/xvid (56 MB) - quicktime (66 MB)

Abstract
We present a new technique for reconstructing a single shape and its non-rigid motion from 3D scanning data. Our algorithm takes a set of time-varying unstructured sample points that show partial views of a deforming object as input and reconstructs a single shape and a deformation field that fit the data. This representation yields dense correspondences for the whole sequence, as well as a completed 3D shape in every frame. In addition, the algorithm automatically removes spatial and temporal noise artifacts and outliers from the raw input data. Unlike previous methods, the algorithm does not require any shape template but computes a fitting shape automatically from the input data ...

A Graph-Based Approach to Symmetry Detection

A Graph-Based Approach to Symmetry Detection
A. Berner, M. Bokeloh, M. Wand, A. Schilling, H.-P. Seidel, IEEE/EG International Symposium on Volume and Point-Based Graphics, 2008
Project Page (Paper and Slides)

Abstract
Symmetry detection aims at discovering redundancy in the form of recurring structures in geometric objects. In this paper, we present a new symmetry detection algorithm for geometry represented as point clouds that is based on analyzing a graph of surface features. We combine a general feature detection scheme with a RANSAC-based randomized subgraph searching algorithm in order to reliably detect recurring patterns of locally unique structures...

Slippage Features

Slippage Features
M. Bokeloh, A. Berner, M. Wand, H.-P. Seidel, A. Schilling, Technical Report, WSI-2008-03, University of Tuebingen, 2008
paper pdf (6 MB) - Poster presentation at Symposium on Geometry Processing 2008 - poster pdf (4 MB)

Abstract
In this report, we present a novel feature detection technique for unstructured point clouds. We introduce a generalized concept of geometric features that detects locally uniquely identifiable keypoints as centroids of area with locally minimal slippage. We extend the concept to multiple scales and extract features using multi-scale mean shift clustering. In order to validate matches between feature points, we employ a two stage technique that ...

Processing and Interactive Editing of Huge Point Clouds from 3D Scanners

Processing and Interactive Editing of Huge Point Clouds from 3D Scanners
M. Wand, A. Berner, M. Bokeloh, P. Jenke, A. Fleck, M. Hoffmann, B. Maier, D. Staneker, A.Schilling, H.-P. Seidel, Computers & Graphics, Volume 32, Issue 2, 2008
paper (publisher site)

Abstract
Using our new data structure, we provide a complete tool chain for 3D scanner data processing, from data preprocessing and filtering to manual touch-up and real-time visualization. In particular, we describe an out-of-core outlier removal and bilateral geometry filtering algorithm, ....

Interactive Editing of Large Point Clouds

Interactive Editing of Large Point Clouds
M. Wand, A. Berner, M. Bokeloh, A. Fleck, M. Hoffmann, P. Jenke, B. Maier, D. Staneker, A. Schilling, Proceedings Symposium on Point-Based Graphics (PBG '07), 2007
pdf (3.9 MB) - video (46 MB) - software (binary & source)

Abstract
This paper describes a new out-of-core multi-resolution data structure for real-time visualization and interactive editing of large point clouds. In addition, an editing system is discussed that makes use of the novel data structure to provide interactive editing tools for large scanner data sets. The new data structure provides efficient rendering and allows for handling very large data sets using out-of-core storage. Unlike related previous approaches, it also provides dynamic operations for online insertion, deletion and modification of points with time mostly independent of scene complexity...


Short CV