Stefan Peters

Quadtree- and octree-based approach for point data selection in 2D or 3D

This article describes a new automatic quadtree-/octree-based and scale-dependent generalization algorithm for point selection. The benefit toward existing point selection methods is that it preserves global as well as local characteristics of the spatial point distribution and of the spatial point density. It can be applied not only to points in 2D space but also to points in 3D space. In this article, an evaluation of the new point selection method is also provided.

Directed kernel density estimation (DKDE) for time series visualization

The purpose of this article is to investigate the density calculation and representation of spatially and temporally highly dynamic point data sets. We suggest an approach to explore point patterns that have a temporal dimension and therefore introduce an incremental development of the traditional kernel density estimation processes. Based on a movement vector assigned to each moving point, we apply a directed (or tilted) kernel to calculate and visualize the density pattern. The resulting density map recognizes the dynamic behavior of the underlying data points. By applying a shade effect or contour lines, the areas with densely distributed moving points are characterized by directed ‘ripples’ or ‘waves’. This assists the visual analysis and prediction of ‘movement trends’ based on the dynamic points. In our case study, we apply this method to airplane movement data limited to two points in time and we thereby visualize the results for the study area over Germany.

Visualizing Crowd Movement Patterns Using a Directed Kernel Density Estimation

“Classic” kernel density estimations (KDE) can display static densities representing one point in time. It is not possible to visually identify which parts of the densities are moving. Therefore, within this paper we investigate how to display dynamic densities (and the density changes) to identify movement patterns. To deal with a temporal dimension (in our case study a dynamic crowd of individuals) we investigated the application of directed kernel density estimation (DKDE). In a case study we apply the DKDE to a point dataset presenting individuals approaching the Allianz Arena in Munich, Germany, with different speeds from different directions. Calculating the density using a directed kernel with this data, results in a density map indicating the movement direction with a visible “ripple” effect. Ripples move at different rates to the substances in which they occur. That tells us something about crowd dynamics and enables us to visually recognize the parts of the crowds that are moving plus the underlying movement directions.

Pre and Post Earthquake Land Use and Land Cover Identification in Concepción

This paper presents the pre and post earthquake identification of representative land cover and land use scenarios in the metropolitan area of Concepcion in Chile. Significant land use and land cover changes will be exposed and evaluated conducting a temporal analysis of satellite image classifications.

Cartographic enrichment of 3D city models—state of the art and research perspectives

This paper reports on cartographic enrichments of three dimensional geovirtual environments including the representation of 3D city models. In the recent years 3D city models have become effective and powerful tools that support the simulation and visualization of our real world in a more and more realistic and detailed way. At the same time, there is a growing interest in comprising more information in the virtual living environment in addition to interior and exterior geometric features, roof and facade textures. A lot of information is related to houses, floors, flats, rooms, etc. but also to persons or specific features at certain urban locations. The paper presents the state of the art of cartographic principles in 3D city models, discusses approaches of cartographic enrichments with the aim to bring added values to the visual exploration of 3D geovirtual environments and reveals missing cartographic design rules within this area.

Visual Analysis of Lightning Data Using Space–Time-Cube

This paper describes a framework for a visual analysis of lightning data described by 3D coordinates and the precise occurrence time. First lightning cells are detected and tracked. After that we developed a GUI (interactive graphic user interface) in order to enable the visual exploration of movement patterns and other characteristics of lightning cells. In particular we present different visual concepts for the dynamic lightning cells and tracks within a Space–Time-Cube and a 3D view. Furthermore a statistical analysis is presented. The developed GUI which aims to support decision making includes the visual and statistical representation of cell features as centroid, extension, density, size etc., within a specific temporal and spatial range of interest.

Visual analysis for nowcasting of multidimensional lightning data

Globally, most weather-related damages are caused by thunderstorms. Besides floods, strong wind, and hail, one of the major thunderstorm ground effects is lightning. Therefore, lightning investigations, including detection, cluster identification, tracking, and nowcasting are essential. To enable reliable decisions, current and predicted lightning cluster- and track features as well as analysis results have to be represented in the most appropriate way. Our paper introduces a framework which includes identification, tracking, nowcasting, and in particular visualization and statistical analysis of dynamic lightning data in three-dimensional space. The paper is specifically focused on enabling users to conduct the visual analysis of lightning data for the purpose of identification and interpretation of spatial-temporal patterns embedded in lightning data, and their dynamics. A graphic user interface (GUI) is developed, wherein lightning tracks and predicted lightning clusters, including their prediction certainty, can be investigated within a 3D view or within a Space-Time-Cube. In contrast to previous work, our approach provides insight into the dynamics of past and predicted 3D lightning clusters and cluster features over time. We conclude that an interactive visual exploration in combination with a statistical analysis can provide new knowledge within lightning investigations and, thus, support decision-making in weather forecast or lightning damage prevention.

Interactive Scale-dependent multidimensional Point Data Selection using enhanced Polarization Transformation

Different fields such as Geovisualization, Web mapping or thematic and topographic cartography all need to incorporate a most recognizable and faithful representation of the real world by different map objects at different scales. The objective of this work was to enhance the existing point selection method - the Polarization Transformation - to an automatic scaledependent point data selection method for multidimensional point data sets, which is implemented in an interactive (Web-) user interface. Benefits of the new method are that in the resulting point selection the global as well as the local characteristics of the spatial point distribution and of the spatial point density are preserved; both for 2D- and 3D- point data sets. Within an interactive user interface the user can upload a point data set, define either the achieved output scale or the wanted number of points to be selected. Then the determined results using the enhanced polarization approach are shown in 2D or 3D to the user. In this work an existing 2D point selection evaluation method for points, based on Voronoi areas, was enhanced for 3D point selection evaluation by using Voronoi volumes. Thus the evaluation verified the similarity of point density and distribution before and after the point data selection.

Establishment and potential spread of the introduced spotted-thighed frog, Litoria cyclorhyncha (Ranoidea cyclorhynchus), in South Australia

ABSTRACT Litoria cyclorhyncha is a hylid frog native to southwest Western Australia (WA). It was first recorded in South Australia (SA) in 2000 and has established a breeding population in Streaky Bay on the western Eyre Peninsula since at least 2011. L. cyclorhyncha is a relatively large predatory frog that presents a potential threat to fauna and ecosystem processes in SA and eastern Australia. This study examines the invasion history and current and potential future distributions of this frog using historical records, field surveys and species distribution modelling (SDM). The historical records in SA suggest human-assisted dispersal through transport networks. Field surveys throughout the Eyre Peninsula during 2016–2017 detected three native species of frogs but no additional breeding populations of L. cyclorhyncha outside of Streaky Bay. Within Streaky Bay, frog abundance appears to be concentrated around permanent water bodies, but the species is also well established in urban habitats. SDM suggests that suitable environmental conditions exist for L. cyclorhyncha in southern and eastern Australia. This, and the frog’s ability to disperse over long distances, suggests considerable potential for the species to become invasive. As L. cyclorhyncha has potential to significantly impact biodiversity and ecosystems, management strategies are urgently needed.