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Visibility Analysis with the Multiscale Implicit TIN 总被引:1,自引:0,他引:1
David B. Kidner rew J. Sparkes Mark I. Dorey J. Mark Ware & Christopher B. Jones 《Transactions in GIS》2001,5(1):19-37
Visibility analysis is now a key function of many geographical information systems. It is also one of the most contentious tools, as it is notoriously prone to error. The paper will demonstrate the versatility of the Multiscale Implicit Triangulated Irregular Network (TIN) for the application of intervisibility analysis at multiple resolutions. This approach allows for the integration of three-dimensional (3D) topographic features with the terrain surface. The multiscale TINs are derived from generalising digital contours at a variety of lateral tolerances. The models' performances are evaluated from an extensive field study undertaken in the South Wales valleys. Results suggest that the accuracy of intervisibility analysis is very dependent upon the availability of good quality 3D topographic data. In our study, such data were shown to improve visibility performance by more than 44% over its bare-earth TIN equivalent. Interestingly, generalisation of the TINs had very little effect on visibility performance. In addition, a Monte Carlo approach to sensitivity analysis was found to be detrimental to the accuracy of visibility prediction in the full terrain and topographic models. However, this probable approach can improve intervisibility performance by up to 18% on a bare-earth TIN. The range of these visibility modelling scenarios demonstrate the flexibility of the Multiscale Implicit TIN for digital surface modelling. 相似文献
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This paper examines the use of multi‐agent simulations (MAS) to model the petrol market. The development of a purely agent based model for petrol prices is presented. Failings within this model are discussed and an alternative strategy for controlling the price of each petrol station based on population of customers is considered. Individual level modelling of customers is too computationally intensive; therefore a spatial interaction model was used to estimate the sales and linked to the agent system to create a hybrid model. To evaluate how effective this hybrid model was, a comparison was made with an existing data set of real petrol prices collected over a two month period. This was achieved both statistically and visually with the use of a Geographical Information System (GIS). Experimentation revealed that the hybrid model outperformed the agent model. Investigation into the behaviour and sensitivity of the system (for example, how prices diffuse spatially) was undertaken by means of idealised simulations. 相似文献
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Seismogenic zone structure beneath the Nicoya Peninsula, Costa Rica, from three-dimensional local earthquake P- and S-wave tomography 总被引:3,自引:0,他引:3
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Audra Baleisis Ofer Lahav rew J. Loan & Jasper V. Wall 《Monthly notices of the Royal Astronomical Society》1998,297(2):545-558
We calculate the expected amplitude of the dipole and higher spherical harmonics in the angular distribution of radio galaxies. The median redshift of radio sources in existing catalogues is z ∼ 1, which allows us to study large-scale structure on scales between those accessible to present optical and infrared surveys, and that of the cosmic microwave background (CMB). The dipole is a result of two effects which turn out to be of comparable magnitude: (i) our motion with respect to the CMB, and (ii) large-scale structure, parametrized here by a family of cold dark matter power-spectra. We make specific predictions for the Green Bank 1987 (87GB) and Parkes–MIT–NRAO (PMN) catalogues, which in our combined catalogue include ∼ 40 000 sources brighter than 50 mJy at 4.85 GHz, over about 70 per cent of the sky. For these relatively sparse catalogues both the motion and large-scale structure dipole effects are expected to be smaller than the Poisson shot noise. However, we detect dipole and higher harmonics in the combined 87GB–PMNraw catalogue which are far larger than expected. We attribute this to a 2 per cent flux mismatch between the two catalogues. Ad hoc corrections made in an effort to match the catalogues may suggest a marginal detection of a dipole. To detect a dipole and higher harmonics unambiguously, a catalogue with full sky coverage and ∼ 106 sources is required. We also investigate the existence and extent of the supergalactic plane in the above catalogues. In a strip of ± 10° of the standard supergalactic equator, we find a 3 σ detection in PMNraw , but only 1 σ in 87 GBraw . We briefly discuss the implications of ongoing surveys such as FIRST and NVSS and follow-up redshift surveys. 相似文献
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Jason K Blackburn rew Curtis Frances Currin Mujica Farrell Jones Patricia Dorn Rosamond Coates 《Transactions in GIS》2008,12(2):249-265
This article describes a web‐based data entry and GIS‐driven mapping system designed for an ethnographic and entomological survey of Chagas’ disease, an emerging zoonotic disease, and Triatoma dimidiata, a primary vector, in the Los Tuxtlas region of Veracruz, Mexico. To better understand this disease in the region, a collaborative, multi‐disciplinary study was initiated to conduct a spatial investigation of T. dimidiata and a community‐by‐community survey of local perceptions of the disease. In order to facilitate such a collaborative effort the CODES‐GIS was developed. This system allows for (near) real‐time mapping, analyses, disease reporting, and results sharing. CODES‐GIS provides a framework for a research team working in a remote area with limited technology, software, or GIS expertise to benefit from (near) real‐time spatial analyses performed at collaborating institutions. The system is bi‐directional, where field personnel can upload data to the system for field‐based map production. Likewise, laboratory personnel can upload diagnostics data for viewing by field personnel. In this way, the system provides a virtual link between the field and the laboratory to increase the speed at which results are returned to the local community. The CODES‐GIS is described along with a selection of study results. 相似文献
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