arXiv subjects

Tim Hegemann

Publications and source records attributed to Tim Hegemann.

4 recordsLinked to original sources

arXiv2026

Chunky Chains: Graph Drawings on Small Screens

We introduce Chunky Chains, a graph drawing style designed for small screens such as smartphones, where vertical scrolling is the dominant means of interaction. A Chunky Chain consists of a vertical chain of chord diagrams, called buckets. Vertices are placed as circular arcs on bucket boundaries, and edges are drawn inside a bucket or through gate nodes connecting consecutive buckets. Since every bucket contains only a bounded number of vertices, the drawing has bounded width. The combinatorial core is the choice of a bucket arrangement. Given a capacity $c$, the vertices are partitioned into an ordered set of buckets, each of size at most $c$. Edges whose endpoints lie in the same or in adjacent buckets are short. Edges that are "skipping" at least one bucket are long, and we draw them only partially. The goal is to minimize the number of long edges. We present a combinatorial framework for producing high quality Chunky Chains and analyze the complexity of its steps. We develop exact and heuristic algorithms, and experimentally evaluate their effectiveness. Our experiments show that many real-world graphs have good Chunky Chain visualizations. In a case study, we discuss Chunky Chains for graphs with certain temporal features.

cs.DS↗

arXiv2025

Optimizing Wiggle in Storylines

A storyline visualization shows interactions between characters over time. Each character is represented by an x-monotone curve. Time is mapped to the x-axis, and groups of characters that interact at a particular point $t$ in time must be ordered consecutively in the y-dimension at $x=t$. The predominant objective in storyline optimization so far has been the minimization of crossings between (blocks of) characters. Building on this work, we investigate another important, but less studied quality criterion, namely the minimization of wiggle, i.e., the amount of vertical movement of the characters over time. Given a storyline instance together with an ordering of the characters at any point in time, we show that wiggle count minimization is NP-complete. In contrast, we provide algorithms based on mathematical programming to solve linear wiggle height minimization and quadratic wiggle height minimization efficiently. Finally, we introduce a new method for routing character curves that focuses on keeping distances between neighboring curves constant as long as they run in parallel. We have implemented our algorithms, and we conduct a case study that explores the differences between the three optimization objectives. We use existing benchmark data, but we also present a new use case for storylines, namely the visualization of rolling stock schedules in railway operation.

cs.DS↗

arXiv2023

Morphing Graph Drawings in the Presence of Point Obstacles

A crossing-free morph is a continuous deformation between two graph drawings that preserves straight-line pairwise noncrossing edges. Motivated by applications in 3D morphing problems, we initiate the study of morphing graph drawings in the plane in the presence of stationary point obstacles, which need to be avoided throughout the deformation. As our main result, we prove that it is NP-hard to decide whether such an obstacle-avoiding 2D morph between two given drawings of the same graph exists. In fact, this statement remains true even in the severely restricted special case where only three vertices have to change positions. This is in sharp contrast to the classical case without obstacles, where there is an efficiently verifiable (necessary and sufficient) criterion for the existence of a morph. Further, we provide several combinatorial results related to conditions under which the existence of a morph between two drawings of a graph can or cannot be prevented by the placement of a given number of point obstacles.

cs.CG↗

arXiv2023

A Simple Pipeline for Orthogonal Graph Drawing

Orthogonal graph drawing has many applications, e.g., for laying out UML diagrams or cableplans. In this paper, we present a new pipeline that draws multigraphs orthogonally, using few bends, few crossings, and small area. Our pipeline computes an initial graph layout, then removes overlaps between the rectangular nodes, routes the edges, orders the edges, and nudges them, that is, moves edge segments in order to balance the inter-edge distances. Our pipeline is flexible and integrates well with existing approaches. Our main contribution is (i) an effective edge-nudging algorithm that is based on linear programming, (ii) a selection of simple algorithms that together produce competitive results, and (iii) an extensive experimental comparison of our pipeline with existing approaches using standard benchmark sets and metrics.

cs.CG↗