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- David Eppstein, Marc J. van Kreveld, Bettina Speckmann, Frank Staals
- Int. J. Comput. Geometry Appl.
- 2013

The collective motion of a set of moving entities like people, birds, or other animals, is characterized by groups arising, merging, splitting, and ending. Given the tra-jectories of these entities, we define and model a structure that captures all of such changes using the Reeb graph, a concept from topology. The trajectory grouping structure has three… (More)

- Peter Eades, Meng-Wei Chang, +50 authors Daniel Weiskopf
- 2013

- Irina Kostitsyna, Marc J. van Kreveld, Maarten Löffler, Bettina Speckmann, Frank Staals
- Symposium on Computational Geometry
- 2015

In recent years trajectory data has become one of the main types of geographic data, and hence algorithmic tools to handle large quantities of trajectories are essential. A single trajectory is typically represented as a sequence of time-stamped points in the plane. In a collection of trajectories one wants to detect maximal groups of moving entities and… (More)

- Joachim Gudmundsson, Marc J. van Kreveld, Frank Staals
- SIGSPATIAL/GIS
- 2013

We study one of the basic tasks in moving object analysis, namely the location of <i>hotspots</i>. A hotspot is a (small) region in which an entity spends a significant amount of time. Finding such regions is useful in many applications, for example in segmentation, clustering, and locating popular places. We may be interested in locating a minimum size… (More)

- Ferran Hurtado, Maarten Löffler, +4 authors Frank Staals
- ISAAC
- 2013

We study the problem of visibility in polyhedral terrains in the presence of multiple viewpoints. We consider a triangulated terrain with m > 1 viewpoints (or guards) located on the terrain surface. A point on the terrain is considered visible if it has an unobstructed line of sight to at least one viewpoint. We study several natural and fundamental… (More)

- Boris Aronov, Anne Driemel, Marc J. van Kreveld, Maarten Löffler, Frank Staals
- ACM Trans. Algorithms
- 2015

In the trajectory segmentation problem, we are given a polygonal trajectory with <i>n</i> vertices that we have to subdivide into a minimum number of disjoint segments (subtrajectories) that all satisfy a given criterion. The problem is known to be solvable efficiently for <i>monotone</i> criteria: criteria with the property that if they hold on a certain… (More)

- Arthur van Goethem, Marc J. van Kreveld, Maarten Löffler, Bettina Speckmann, Frank Staals
- Symposium on Computational Geometry
- 2016

We present algorithms and data structures that support the interactive analysis of the grouping structure of one-, two-, or higher-dimensional time-varying data while varying all defining parameters. Grouping structures characterise important patterns in the temporal evaluation of sets of time-varying data. We follow Buchin et al. [9] who define groups… (More)

- Maarten Löffler, Martin Nöllenburg, Frank Staals
- CIAC
- 2015

Point feature map labeling is a geometric problem, in which a set of input points must be labeled with a set of disjoint rectangles (the bounding boxes of the label texts). Typically, labeling models either use internal labels, which must touch their feature point, or external (boundary) labels, which are placed on one of the four sides of the input points'… (More)