Numerical Evaluation of Pathline Predicates of the Benguela Upwelling System

Using simulation data of a regional ocean model, Nardini et al. applied pathline predicates for a detailed post-hoc analysis of the Benguela upwelling system. In this work, we evaluate the accuracy of this technique. Using different temporal samplings, we aim at finding minimum requirements for the temporal resolution of the flow data in the context of retroactive particle pathline techniques. Besides the flow field, our simulation data contains synthetic tracer fields for different tracer source regions. Using the flow data, dense trajectories are computed to enable deriving ”emulated tracer fields” based on the local ratio of pathline particles originating from tracer source regions to other ones, which can then be compared to the original tracer fields. We find that the emulated tracer concentrations are overestimated in comparison to the original ones. However, the shape of the regions with high tracer concentration can be reproduced

The Making of Continuous Colormaps

Continuous colormaps are integral parts of many visualization techniques, such as heat-maps, surface plots, and flow visualization. Despite that the critiques of rainbow colormaps have been around and well-acknowledged for three decades, rainbow colormaps are still widely used today. One reason behind the resilience of rainbow colormaps is the lack of tools for users to create a continuous colormap that encodes semantics specific to the application concerned. In this paper, we present a web-based software system, CCC-Tool (short for Charting Continuous Colormaps) under the URL https://ccctool.com, for creating, editing, and analyzing such application-specific colormaps. We introduce the notion of “colormap pecification (CMS)” that maintains the essential semantics required for defining a color mapping scheme. We provide users with a set of advanced utilities for constructing CMS’s with various levels of complexity, examining their quality attributes using different plots, and exporting them to external application software. We present two case studies, demonstrating that the CCC-Tool can help domain scientists as well as visualization experts in designing semantically-rich colormaps

Visual Study of the Benguela Upwelling System using Pathline Predicates

Due to the nutrient-rich water transported to the upper layer of the ocean, coastal upwelling systems are regions especially important for marine life and fishery. In this work, we focus on a visual analysis of the spatio-temporal structure of the Benguela upwelling system using pathline predicates. Based on the 3D flow field from an ocean model simulation, we first derive space- filling trajectories covering the full model grid. From these, we select and visualize pathlines related to upwelling. In a second step, we derive a 3D scalar field representing the pathline density, which is visualized using volume rendering techniques. Further analyses of the pathlines show a distinct annual cycle in the upwelling activity, which fits well to observation-based analyses found in literature