@inproceedings{GreenhalghBenfordDrozdetal.2007, author = {Greenhalgh, Chris and Benford, Steve and Drozd, Adam and Flintham, Martin and Hampshire, Alastair and Oppermann, Leif and Smith, Keir and Tycowicz, Christoph von}, title = {Addressing Mobile Phone Diversity in Ubicomp Experience Development}, volume = {4717}, booktitle = {UbiComp 2007: Ubiquitous Computing, 9th International Conference}, doi = {10.1007/978-3-540-74853-3_26}, pages = {447 -- 464}, year = {2007}, abstract = {Mobile phones are a widely-available class of device with supporting communications infrastructure which can be appropriated and exploited to support ubicomp experiences. However mobile phones vary hugely in their capabilities. We explore how a single dimension of phone application type embodies the critical trade-off between capability and availability, i.e. between what can be done and the fraction of potential participants' phones that can do this. We describe four different mobile phone ubicomp experiences that illustrate different points along this continuum (SMS, WAP/Web, and J2ME, Python and native applications) and the common software platform/toolkit, EQUIP2, that has been co-developed to support them. From this we propose four development strategies for addressing mobile phone diversity: prioritise support for server development (including web integration), migrate functionality between server(s) and handset(s), support flexible communication options, and use a loosely coupled (data-driven and component-based) software approach.}, language = {en} } @phdthesis{Tycowicz2014, author = {Tycowicz, Christoph von}, title = {Concepts and Algorithms for the Deformation, Analysis, and Compression of Digital Shapes}, doi = {10.17169/refubium-4697}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:188-fudissthesis000000096721-7}, year = {2014}, abstract = {This thesis concerns model reduction techniques for the efficient numerical treatment of physical systems governing the deformation behavior of geometrically complex shapes. We present new strategies for the construction of simplified, low-dimensional models that capture the main features of the original complex system and are suitable for use in interactive computer graphics applications. To demonstrate the effectiveness of the new techniques we propose frameworks for real-time simulation and interactive deformation-based modeling of elastic solids and shells and compare them to alternative approaches. In addition, we investigate differential operators that are derived from the physical models and hence can serve as alternatives to the Laplace-Beltrami operator for applications in modal shape analysis. Furthermore, this thesis addresses the compression of digital shapes. In particular, we present a lossless compression scheme that is adapted to the special characteristics of adaptively refined, hierarchical meshes.}, language = {en} } @incollection{PolthierBobenkoHildebrandtetal.2014, author = {Polthier, Konrad and Bobenko, Alexander and Hildebrandt, Klaus and Kornhuber, Ralf and Tycowicz, Christoph von and Yserentant, Harry and Ziegler, G{\"u}nter M.}, title = {Geometry processing}, volume = {1}, booktitle = {MATHEON - Mathematics for Key Technologies}, publisher = {EMS Publishing House}, isbn = {978-3-03719-137-8}, doi = {10.4171/137}, pages = {341 -- 355}, year = {2014}, language = {en} } @incollection{OppermannJacobsWatkinsetal.2007, author = {Oppermann, Leif and Jacobs, R. and Watkins, M. and Shackford, R. and Tycowicz, Christoph von and Wright, M. and Capra, M. and Greenhalgh, Chris and Benford, Steve}, title = {Love City: A Text-Driven, Location-Based Mobile Phone Game Played Between 3 Cities}, volume = {2}, booktitle = {Pervasive Gaming Applications - A Reader for Pervasive Gaming Research}, publisher = {Shaker Verlag}, isbn = {978-3-8322-6224-2}, pages = {285 -- 312}, year = {2007}, language = {en} } @incollection{GreenhalghBenfordDrozdetal.2007, author = {Greenhalgh, Chris and Benford, Steve and Drozd, Adam and Flintham, Martin and Hampshire, Alastair and Oppermann, Leif and Smith, Keir and Tycowicz, Christoph von}, title = {EQUIP2: A Platform for Mobile Phone-based Game Development}, volume = {1}, booktitle = {Concepts and Technologies for Pervasive Games - A Reader for Pervasive Gaming Research}, publisher = {Shaker Verlag}, isbn = {978-3-8322-6223-5}, pages = {153 -- 178}, year = {2007}, language = {en} } @article{vonTycowiczAmbellanMukhopadhyayetal.2018, author = {von Tycowicz, Christoph and Ambellan, Felix and Mukhopadhyay, Anirban and Zachow, Stefan}, title = {An Efficient Riemannian Statistical Shape Model using Differential Coordinates}, volume = {43}, journal = {Medical Image Analysis}, number = {1}, doi = {10.1016/j.media.2017.09.004}, pages = {1 -- 9}, year = {2018}, abstract = {We propose a novel Riemannian framework for statistical analysis of shapes that is able to account for the nonlinearity in shape variation. By adopting a physical perspective, we introduce a differential representation that puts the local geometric variability into focus. We model these differential coordinates as elements of a Lie group thereby endowing our shape space with a non-Euclidean structure. A key advantage of our framework is that statistics in a manifold shape space becomes numerically tractable improving performance by several orders of magnitude over state-of-the-art. We show that our Riemannian model is well suited for the identification of intra-population variability as well as inter-population differences. In particular, we demonstrate the superiority of the proposed model in experiments on specificity and generalization ability. We further derive a statistical shape descriptor that outperforms the standard Euclidean approach in terms of shape-based classification of morphological disorders.}, language = {en} } @article{BrandtTycowiczHildebrandt2016, author = {Brandt, Christopher and Tycowicz, Christoph von and Hildebrandt, Klaus}, title = {Geometric Flows of Curves in Shape Space for Processing Motion of Deformable Objects}, volume = {35}, journal = {Computer Graphics Forum}, number = {2}, doi = {10.1111/cgf.12832}, year = {2016}, abstract = {We introduce techniques for the processing of motion and animations of non-rigid shapes. The idea is to regard animations of deformable objects as curves in shape space. Then, we use the geometric structure on shape space to transfer concepts from curve processing in Rn to the processing of motion of non-rigid shapes. Following this principle, we introduce a discrete geometric flow for curves in shape space. The flow iteratively replaces every shape with a weighted average shape of a local neighborhood and thereby globally decreases an energy whose minimizers are discrete geodesics in shape space. Based on the flow, we devise a novel smoothing filter for motions and animations of deformable shapes. By shortening the length in shape space of an animation, it systematically regularizes the deformations between consecutive frames of the animation. The scheme can be used for smoothing and noise removal, e.g., for reducing jittering artifacts in motion capture data. We introduce a reduced-order method for the computation of the flow. In addition to being efficient for the smoothing of curves, it is a novel scheme for computing geodesics in shape space. We use the scheme to construct non-linear B{\´e}zier curves by executing de Casteljau's algorithm in shape space.}, language = {en} } @inproceedings{HanikHegevonTycowicz2022, author = {Hanik, Martin and Hege, Hans-Christian and von Tycowicz, Christoph}, title = {A Nonlinear Hierarchical Model for Longitudinal Data on Manifolds}, booktitle = {2022 IEEE 19th International Symposium on Biomedical Imaging (ISBI)}, arxiv = {http://arxiv.org/abs/2202.01180}, doi = {10.1109/ISBI52829.2022.9761465}, pages = {1 -- 5}, year = {2022}, abstract = {Large longitudinal studies provide lots of valuable information, especially in medical applications. A problem which must be taken care of in order to utilize their full potential is that of correlation between intra-subject measurements taken at different times. For data in Euclidean space this can be done with hierarchical models, that is, models that consider intra-subject and between-subject variability in two different stages. Nevertheless, data from medical studies often takes values in nonlinear manifolds. Here, as a first step, geodesic hierarchical models have been developed that generalize the linear ansatz by assuming that time-induced intra-subject variations occur along a generalized straight line in the manifold. However, this is often not the case (e.g., periodic motion or processes with saturation). We propose a hierarchical model for manifold-valued data that extends this to include trends along higher-order curves, namely B{\´e}zier splines in the manifold. To this end, we present a principled way of comparing shape trends in terms of a functional-based Riemannian metric. Remarkably, this metric allows efficient, yet simple computations by virtue of a variational time discretization requiring only the solution of regression problems. We validate our model on longitudinal data from the osteoarthritis initiative, including classification of disease progression.}, language = {en} } @misc{AmbellanHanikvonTycowicz2021, author = {Ambellan, Felix and Hanik, Martin and von Tycowicz, Christoph}, title = {Morphomatics: Geometric morphometrics in non-Euclidean shape spaces}, doi = {10.12752/8544}, year = {2021}, abstract = {Morphomatics is an open-source Python library for (statistical) shape analysis developed within the geometric data analysis and processing research group at Zuse Institute Berlin. It contains prototype implementations of intrinsic manifold-based methods that are highly consistent and avoid the influence of unwanted effects such as bias due to arbitrary choices of coordinates.}, language = {en} } @article{OehmeMoewisBoethetal.2024, author = {Oehme, Stephan and Moewis, Philippe and Boeth, Heide and Bartek, Benjamin and von Tycowicz, Christoph and Ehrig, Rainald and Duda, Georg and Jung, Tobias}, title = {Altered knee kinematics after posterior cruciate single-bundle reconstruction - a comprehensive prospective biomechanical in vivo analysis}, volume = {12}, journal = {Frontiers in Bioengineering and Biotechnology}, doi = {10.3389/fbioe.2024.1322136}, year = {2024}, language = {en} }