Line generalisation by repeated elimination of the smallest area

CISRG discussion paper ; 1

Cartographic algorithms : problems of implementation and evaluation and the impact of digitising errors

CISRG discussion paper ;

The Douglas-Peucker algorithm for line simplification : re-evaluation through visualisation

CISRG discussion paper ;

Dynamics and controls of urban heat sink and island phenomena in a desert city:development of a local climate zone scheme using remotely-sensed inputs

This study aims to determine the dynamics and controls of Surface Urban Heat Sinks (SUHS) and Surface Urban Heat Islands (SUHI) in desert cities, using Dubai as a case study. A Local Climate Zone (LCZ) schema was developed to subdivide the city into different zones based on similarities in land cover and urban geometry. Proximity to the Gulf Coast was also determined for each LCZ. The LCZs were then used to sample seasonal and daily imagery from the MODIS thermal sensor to determine Land Surface Temperature (LST) variations relative to desert sand. Canonical correlation techniques were then applied to determine which factors explained the variability between urban and desert LST. Our results indicate that the daytime SUHS effect is greatest during the summer months (typically ∼3.0 °C) with the strongest cooling effects in open high-rise zones of the city. In contrast, the night-time SUHI effect is greatest during the winter months (typically ∼3.5 °C) with the strongest warming effects in compact mid-rise zones of the city. Proximity to the Arabian Gulf had the largest influence on both SUHS and SUHI phenomena, promoting daytime cooling in the summer months and night-time warming in the winter months. However, other parameters associated with the urban environment such as building height had an influence on daytime cooling, with larger buildings promoting shade and variations in airflow. Likewise, other parameters such as sky view factor contributed to night-time warming, with higher temperatures associated with limited views of the sky

Combining physiological, environmental and locational sensors for citizen-oriented health applications

This work investigates the potential of combining the outputs of multiple low-cost sensor technologies for the direct measurement of spatio-temporal variations in phenomena that exist at the interface between our bodies and the environment. The example used herein is the measurement of personal exposure to traffic pollution, which may be considered as a function of the concentration of pollutants in the air and the frequency and volume of that air which enters our lungs. The sensor-based approach described in this paper removes the ‘traditional’ requirements either to model or interpolate pollution levels or to make assumptions about the physiology of an individual. Rather, a wholly empirical analysis into pollution exposure is possible, based upon high-resolution spatio-temporal data drawn from sensors for NO2, nasal airflow and location (GPS). Data are collected via a custom smartphone application and mapped to give an unprecedented insight into exposure to traffic pollution at the individual level. Whilst the quality of data from low-cost miniaturised sensors is not suitable for all applications, there certainly are many applications for which these data would be well suited, particularly those in the field of citizen science. This paper demonstrates both the potential and limitations of sensor-based approaches and discusses the wider relevance of these technologies for the advancement of citizen science

Using fractal analysis of crown images to measure the structural condition of trees

Observations of tree canopy structure are routinely used as an indicator of tree condition for the purposes of monitoring tree health, assessing habitat characteristics or evaluating the potential risk of tree failure. Trees are assigned to broad categories of structural condition using largely subjective methods based upon ground-based, visual observations by a surveyor. Such approaches can suffer from a lack of consistency between surveyors; are qualitative in nature and have low precision. In this study, a technique is developed for acquiring, processing and analysing hemispherical images of sessile oak (Quercus petraea (Matt.) Liebl.) tree crowns. We demonstrate that by calculating the fractal dimensions of tree crown images it is possible to define a continuous measurement scale of structural condition and to be able to quantify intra-category variance of tree crown structure. This approach corresponds with traditional categorical methods; however, we recognize that further work is required to precisely define interspecies thresholds. Our study demonstrates that this approach has the potential to form the basis of a new, transferable and objective methodology that can support a wide range of uses in arboriculture, ecology and forest science

Spatio-temporal challenges in representing wildlife disturbance within a GIS

Assessing the potential environmental impacts of disturbance on protected species during and after the development process is a legislative requirement in most nations. However, the restrictions that this legislation places on developers are often based on limited ecological understanding, over-simplified methodologies, less-than-robust data and the subjective interpretations of field ecologists. Consequently, constraints may be imposed with no transparent methodology behind them to the frustration of, and occasionally large expense to, developers. Additionally, protected species numbers continue to decline and biodiversity continues to be threatened. This paper describes a GIS conceptual model for assessing ecological disturbance vulnerability, based upon a case study development in Scotland. First, uncertainties in traditional methods of recording and representing ecological features with GIS are reviewed such that they may be better accounted for in the disturbance model. Second, by incorporating temporal fluctuations in ecological behaviour into the disturbance susceptibility concept, it is argued that it is possible to synchronise development with conservation requirements. Finally, a method is presented to account for disturbance tolerances at the scale of the individual animal. It is anticipated that this model will enable environmental impact assessors to produce more robust analyses of wildlife disturbance risk and facilitate synchronisation between development and wildlife vulnerability to minimise disturbance and better avoid delays to the works programme

Resolving the Broccoli Problem: Identifying Optimal Computational Algorithms for the Accuracy Assessment of Tree Delineations from Remotely-sensed Data

For many different investigative purposes, trees and forests are aerially scanned using light detection and ranging (LiDAR). Often, this also requires the manual measurement of ground reference (GR) plots within the LiDAR scan. Upon analysis, there is regularly a mismatch between the alignment of GR and LiDAR tree locations, crown areas and tree heights. This anomaly is frequently overlooked and under-reported in the current literature. This study investigates the suitability of match pairing algorithms for the quantification of misalignment errors between two datasets representing GR and LiDAR data, and recommends an algorithm for accurately quantifying match-pairing differences