The Douglas-Peucker algorithm for line simplification: Re-evaluation through visualization

The primary aim of this paper is to illustrate the value of visualization in cartography and to indicate that tools for the generation and manipulation of realistic images are of limited value within this application. This paper demonstrates the value of visualization within one problem in cartography, namely the generalisation of lines. It reports on the evaluation of the Douglas-Peucker algorithm for line simplification. Visualization of the simplification process and of the results suggest that the mathematical measures of performance proposed by some other researchers are inappropriate, misleading and questionable

Cartographic Algorithms: Problems of Implementation and Evaluation and the Impact of Digitising Errors

Cartographic generalisation remains one of the outstanding challenges in digital cartography and Geographical Information Systems (GIS). It is generally assumed that computerisation will lead to the removal of spurious variability introduced by the subjective decisions of individual cartographers. This paper demonstrates through an in‐depth study of a line simplification algorithm that computerisation introduces its own sources of variability. The algorithm, referred to as the Douglas‐Peucker algorithm in cartographic literature, has been widely used in image processing, pattern recognition and GIS for some 20 years. An analysis of this algorithm and study of some implementations in wide use identify the presence of variability resulting from the subjective decisions of software implementors. Spurious variability in software complicates the processes of evaluation and comparison of alternative algorithms for cartographic tasks. No doubt, variability in implementation could be removed by rigorous study and specification of algorithms. Such future work must address the presence of digitising error in cartographic data. Our analysis suggests that it would be difficult to adapt the Douglas‐Peucker algorithm to cope with digitising error without altering the method. Copyright © 1991, Wiley Blackwell. All rights reserve

The Douglas-Peucker line simplification algorithm : an introduction with programs

CISRG discussion paper ;

Line generalisation by repeated elimination of points

This paper presents a new approach to line generalisation which uses the concept of ‘effective area’ for progressive simplification of a line by point elimination. Two coastlines are used to compare the performance of this, with that of the widely used Douglas-Peucker, algorithm. The results from the area-based algorithm compare favourably with manual generalisation of the same lines. It is capable of achieving both imperceptible minimal simplifications and caricatural generalisations. By careful selection of cutoff values, it is possible to use the same algorithm for scale-dependent and scale-independent generalisations. More importantly, it offers scope for modelling cartographic lines as consisting of features within features so that their geometric manipulation may be modified by application- and/or user-defined rules and weights. The paper examines the merits and limitations of the algorithm and the opportunities it offers for further research and progress in the field of line generalisation. © 1993 Maney Publishing

The clumpiness of molecular clouds: HCO+ (3--2) survey near Herbig-Haro objects

Some well-studied Herbig Haro objects have associated with them one or more cold, dense, and quiescent clumps of gas. We propose that such clumps near an HH object can be used as a general measure of clumpiness in the molecular cloud that contains that HH object. Our aim is to make a survey of clumps around a sample of HH objects, and to use the results to make an estimate of the clumpiness in molecular clouds. All known cold, dense, and quiescent clumps near HH objects are anomalously strong HCO+ emitters. Our method is, therefore, to search for strong HCO+ emission as an indicator of a clump near to an HH object. The searches were made using JCMT and SEST in the HCO+ 3-2 and also H13CO+ 1-0 lines, with some additional searches for methanol and sulphur monoxide lines. The sources selected were a sample of 22 HH objects in which no previous HCO+ emission had been detected. We find that half of the HH objects have clumps detected in the HCO+ 3-2 line and that all searches in H13CO$+ 1-0 lines show evidence of clumpiness. All condensations have narrow linewidths and are evidently unaffected dynamically by the HH jet shock. We conclude that the molecular clouds in which these HH objects are found must be highly heterogeneous on scales of less than 0.1 pc. An approximate calculation based on these results suggests that the area filling factor of clumps affected by HH objects is on the order of 10%. These clumps have gas number densities larger than 3e4 cm-2.Comment: 11 pages, 14 figures. Accepted for publication in Astronomy and Astrophysic

N4WBP5A (Ndfip2), a Nedd4-interacting protein, localizes to multivesicular bodies and the Golgi, and has a potential role in protein trafficking

N4WBP5A (Ndfip2) belongs to an evolutionarily conserved group of Nedd4-interacting proteins with two homologues in mammalian species. We have previously shown that N4WBP5A expression in Xenopus oocytes results in increased cell-surface expression of the epithelial sodium channel. N4WBPs are characterized by one or two amino terminal PPxY motifs and three transmembrane domains. Here we show that both PPxY motifs of N4WBP5A mediate interaction with WW domains of Nedd4 and that N4WBP5A can physically interact with the WW domains of several Nedd4-family proteins. N4WBP5A is ubiquitinated and ubiquitination does not significantly affect the turnover of N4WBP5A protein. Ubiquitination of N4WBP5A is enhanced by Nedd4 and Nedd4-2 expression. N4WBP5A localizes to the Golgi, vesicles associated with the Golgi complex and to multivesicular bodies. We show that the ectopic expression of N4WBP5A inhibits receptor-mediated endocytosis of labelled epidermal growth factor. N4WBP5A overexpression inhibits accumulation of EGF in large endocytic/lysosomal vesicles suggestive of a role for N4WBP5A in protein trafficking. We propose that N4WBP5A acts as an adaptor to recruit Nedd4 family ubiquitin-protein ligases to the protein trafficking machinery.Linda M. Shearwin-Whyatt, Darren L. Brown, Fiona G. Wylie, Jennifer L. Stow and Sharad Kuma

Urban form strongly mediates the allometric scaling of airshed pollution concentrations

We present allometric-scaling relationships between non-point-source emissions of air pollutants and settlement population, using 3030 urban settlements in Great Britain (home to ca. 80% of the population of that region). Sub-linear scalings (slope  0.6) were found for the oxides of nitrogen (NO _x ) and microscopic airborne particles (PM _10  and PM _2.5 ). That is, emissions of these pollutants from larger cities are lower per capita than would be expected when compared to the same population dispersed in smaller settlements. The scalings of traffic-related emissions are disaggregated into a component due to under-use of roads in small settlements and a fraction due to congestion in large settlements. We use these scalings of emissions, along with a scaling related to urban form, to explain quantitatively how and why urban airshed-average air pollutant concentrations also scale with population. Our predicted concentration scaling with population is strongly sub-linear, with a slope about half that of the emissions scaling, consistent with satellite measurements of NO _2  columns over large cities across Europe. We demonstrate that the urban form of a particular settlement can result in the airshed-average air pollution of that settlement being much larger or smaller than expected. We extend our analysis to predict that the likelihood of occurrence of local air pollution hotspots will scale super-linearly with population, a testable hypothesis that awaits suitable data. Our analysis suggests that coordinated management of emissions and urban form would strongly reduce the likelihood of local pollutant hotspots occurring whilst also ameliorating the urban heat island effect under climate change

Chemistry of dense clumps near moving Herbig-Haro objects

Localised regions of enhanced emission from HCO+, NH3 and other species near Herbig-Haro objects (HHOs) have been interpreted as arising in a photochemistry stimulated by the HHO radiation on high density quiescent clumps in molecular clouds. Static models of this process have been successful in accounting for the variety of molecular species arising ahead of the jet; however recent observations show that the enhanced molecular emission is widespread along the jet as well as ahead. Hence, a realistic model must take into account the movement of the radiation field past the clump. It was previously unclear as to whether the short interaction time between the clump and the HHO in a moving source model would allow molecules such as HCO+ to reach high enough levels, and to survive for long enough to be observed. In this work we model a moving radiation source that approaches and passes a clump. The chemical picture is qualitatively unchanged by the addition of the moving source, strengthening the idea that enhancements are due to evaporation of molecules from dust grains. In addition, in the case of several molecules, the enhanced emission regions are longer-lived. Some photochemically-induced species, including methanol, are expected to maintain high abundances for ~10,000 years.Comment: 7 pages, 3 figure

Exploring segregation and sharing in a divided city: A PGIS approach

This article presents a novel exploratory investigation into the location and characteristics of spaces that are segregated and shared between Protestant and Catholic communities in Belfast, Northern Ireland (UK). Focusing on a particularly segregated part of the city, this study uses state-of-the-art participatory geographic information systems (PGIS) and visualization techniques to create qualitative, bottom-up maps of segregation and sharing within the city, as experienced by the people who live there. In doing so, it identifies important and previously unreported patterns in segregation and sharing between sectarian communities, challenging normative approaches to PGIS, illustrating how alternative methods might provide deeper insights into complex social geographies such as those of segregation. Finally, the findings of this work are formulated into a set of hypotheses that can contribute to a future research agenda into segregation and sharing, both in Belfast and in other divided cities

Solar park management and design to boost bumble bee populations

Abstract: Solar photovoltaics is projected to become the dominant renewable, with much capacity being installed as ground-mounted solar parks. Land use change for solar can affect ecosystems across spatial scales and solar parks offer a unique opportunity for ecological enhancement. One compelling potential benefit beginning to be deployed by the solar industry is management for insect pollinators. Specifically, solar parks can provide refuge for pollinators through the provision of suitable habitat, potentially contributing to halting and reversing widespread declines recorded in some pollinator groups. There is scope to both manage and design solar parks for pollinators, but understanding is limited. Using a geographic information system and a process-based pollinator model, we explore how solar park management, size, shape and landscape context might impact ground-nesting bumble bee density, nest density and nest productivity inside existing solar parks and surrounding landscapes in the UK. We show that bumble bee density and nest density is driven by solar park management, with twice as many bumble bees foraging and nesting inside solar parks managed as wildflower meadows, compared to those with only wildflower margins. In comparison, solar park size, shape and landscape context have a smaller impact on bumble bee response inside solar parks. However, large, elongated resource-rich solar parks were most effective at increasing bumble bee density in surrounding landscapes, with implications for local crop pollination. Specifically, there were double the number of foraging bumble bees surrounding large solar parks managed as meadows compared to smaller parks managed as turf grass. If designed and managed optimally, solar parks therefore have the potential to boost local bumble bee density and potentially pollination services to adjacent crops. Our results demonstrate how incorporating biodiversity into solar park management and design decisions could benefit groups such as pollinators and contribute to the wider environmental sustainability of solar parks