1,232 research outputs found

    Generating seamless surfaces for transport and dispersion modeling in GIS

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    A standard use of triangulation in GIS is to model terrain surface using TIN. In many simulation models of physical phenomena, triangulation is often used to depict the entire spatial domain, which may include buildings, landmarks and other surface objects in addition to the terrain surface. Creating a seamless surface of complex building structures together with the terrain is challenging and existing approaches are laborious, time-consuming and error-prone. We propose an efficient and robust procedure using computational geometry techniques to derive triangulated building surfaces from 2D polygon data with a height attribute. We also propose a new method to merge the resultant building surfaces with the triangulated terrain surface to produce a seamless surface for the entire study area. Using Oklahoma City data, we demonstrate the proposed method. The resultant surface is used as the input data for a simulated transport and dispersion event in Oklahoma City. The proposed method can produce the seamless surface data to be used for various types of physical models in a fraction of the time required by previous methods

    Simulation of Range Safety for the NASA Space Shuttle

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    This paper describes a simulation environment that seamlessly combines a number of safety and environmental models for the launch phase of a NASA Space Shuttle mission. The components of this simulation environment represent the different systems that must interact in order to determine the Expectation of casualties (E(sub c)) resulting from the toxic effects of the gas dispersion that occurs after a disaster affecting a Space Shuttle within 120 seconds of lift-off. The utilization of the Space Shuttle reliability models, trajectory models, weather dissemination systems, population models, amount and type of toxicants, gas dispersion models, human response functions to toxicants, and a geographical information system are all integrated to create this environment. This simulation environment can help safety managers estimate the population at risk in order to plan evacuation, make sheltering decisions, determine the resources required to provide aid and comfort, and mitigate damages in case of a disaster. This simulation environment may also be modified and used for the landing phase of a space vehicle but will not be discussed in this paper

    Fast and robust generation of city scale urban ground plan

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    Since the introduction of the concept of Digital Earth, almost every major international city has been re-constructed in the virtual world. A large volume of geometric models describing urban objects has become freely available in public domain via software like Google Earth. Although mostly created for visualization, these urban models can benefit many applications beyond visualization including video games, city scale evacuation plan, traffic simulation and earth phenomenon simulations. However, these urban models are mostly loosely structured and implicitly defined and require tedious manual preparation that usually take weeks if not months before they can be used. In this paper, we present a framework that produces well-defined ground plans from these urban models, an important step in the preparation process. Designing algorithms that can robustly and efficiently handle unstructured urban models at city scale is the main technical challenge. In this work, we show both theoretically and empirically that our method is resolution complete, efficient and numerically stable. Based on our review of the related work, we believe this is the first work that attempts to create urban ground plans automatically from 3D architectural meshes at city level. With the goal of providing greater benefit beyond visualization from this large volume of urban models, our initial results are encouraging.published_or_final_versio

    Spatial Discrepancies between NHDPlus and LIDAR-Derived Stream Networks

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    Many organizations demand that current water resource issues necessitate improved stream network mapping for more accurate and reliable watershed analysis and modeling results, which can ultimately enable better management and policy decisions. Stream network data from the National Hydrography Dataset Plus (NHDPlus) and derived from Light Detection and Ranging (LIDAR) are each widely accepted to be of superior quality compared to many other conventional datasets. Each dataset indicates potential to improve a wide range of water resource applications; NHDPlus for its high spatial accuracy and functionality, and LIDAR-derived networks for their high resolutions. NHDPlus is publicly available and widely used; yet, until recently, high production costs and limited availability of LIDAR data have traditionally limited their widespread use in stream network mapping for water resource applications. However, recently increasing availability and decreasing costs suggest that LIDAR-derived networks could potentially be used to improve many application initiatives. This study analyzes spatial discrepancies between NHDPlus and LIDAR-derived stream network datasets. Results from analyses are intended to contribute information that can lead to improved stream network mapping and water resource applications. Mann-Whitney U and Wilcoxon-Signed Rank tests were first conducted to ascertain statistically significant types of spatial discrepancies existing between the datasets. Spatial autocorrelation analysis was then used to quantify spatial patterns of discrepancies between NHDPlus and LIDAR-derived networks. Next, Kruskal-Wallis tests were conducted to determine associations between local patterns of discrepancies and various landscape characteristics. Lastly, Spearman Rank Correlation tests were used to ascertain relationships between landscape characteristics and discrepancies between networks per catchment. Results indicate that significant types and patterns of spatial discrepancies exist between NHDPlus and LIDAR-derived stream network datasets, and local patterns of the discrepancies are spatially related to various landscape characteristics. These findings imply how spatial discrepancies resulting between NHDPlus and LIDAR-derived networks may lead to differing watershed analysis and modeling results. Collectively, this research contributes building fundamental information for better understanding how to improve stream network mapping and water resource applications

    Modeling the Movement of Septic Water Chloride through a Soil Profile

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    The purpose of this study was to investigate the movement of chloride through a vadose zone located under failed and non-regulated septic tanks of Duhok city, Kurdistan of Iraq, potentially contaminating its groundwater. A physical vadose model (PVM) of a vertical flow direction was built in the laboratory to represent the city soil profile. The size of the PVM was 210 × 122 × 9.7 cm (height, width, and depth). Preliminary soil tests were conducted to better represent the lithology of study area. The PVM was then packed with regional silt clay soil, after modifying its texture, using an innovative packing procedure to preserve natural soil density and porosity. The model was run for a period of three months with newly collected septic water (black water from a septic tank) as an exclusive source of contaminants. Water samples from eight vertically arranged portals representing 12.5, 37.5, 62.5, 87.5, 112.5, 137.5, 162.5, and 187.5 cm levels in the subsurface soil profile were collected on a daily basis and analyzed weekly. Logistic regression and logarithmic models were developed to spatially predict the movement of chloride ions at different sampling depths in the soil profile until the system had reached the equivalent chloride concentration of the septic water or had stabilized. There was a good agreement between the physical model and the statistical models, however each model had its strengths and weaknesses. This study demonstrated that there is a potential for septic water to reach the water table within a 2–3 weeks period. Dilution and dispersion appear to play important roles in the fate and transport of septic water. This study has the potential to help the local authorities predict percolation rates and establish strategies for groundwater management in order to protect the public health

    Iz stranih časopisa

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    U tekstu je dan popis radova koji su objavljeni u stranim časopisima

    Iz stranih časopisa

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    U tekstu je dan popis radova koji su objavljeni u stranim časopisima

    Virtual Worlds and Conservational Channel Evolution and Pollutant Transport Systems (Concepts)

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    Many models exist that predict channel morphology. Channel morphology is defined as the change in geometric parameters of a river. Channel morphology is affected by many factors. Some of these factors are caused either by man or by nature. To combat the adverse effects that man and nature may cause to a water system, scientists and engineers develop stream rehabilitation plans. Stream rehabilitation as defined by Shields et al., states that restoration is the return from a degraded ecosystem back to a close approximation of its remaining natural potential [Shields et al., 2003]. Engineers construct plans that will restore streams back to their natural state by using techniques such as field investigation, analytical models, or numerical models. Each of these techniques is applied to projects based on specified criteria, objectives, and the expertise of the individuals devising the plan. The utilization of analytical and numerical models can be difficult, for many reasons, one of which is the intuitiveness of the modeling process. Many numerical models exist in the field of hydraulic engineering, fluvial geomorphology, landscape architecture, and stream ecology that evaluate and formulate stream rehabilitation plans. This dissertation will explore, in the field of Hydroscience , the creation of models that are not only accurate but also span the different disciplines. The goal of this dissertation is to transform a discrete numerical model (CONCEPTS) into a realistic 3D environment using open source game engines, while at the same time, conveying at least the equivalent information that was presented in the 1D numerical model

    Characterising the ocean frontier : a review of marine geomorphometry

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    Geomorphometry, the science that quantitatively describes terrains, has traditionally focused on the investigation of terrestrial landscapes. However, the dramatic increase in the availability of digital bathymetric data and the increasing ease by which geomorphometry can be investigated using Geographic Information Systems (GIS) has prompted interest in employing geomorphometric techniques to investigate the marine environment. Over the last decade, a suite of geomorphometric techniques have been applied (e.g. terrain attributes, feature extraction, automated classification) to investigate the characterisation of seabed terrain from the coastal zone to the deep sea. Geomorphometric techniques are, however, not as varied, nor as extensively applied, in marine as they are in terrestrial environments. This is at least partly due to difficulties associated with capturing, classifying, and validating terrain characteristics underwater. There is nevertheless much common ground between terrestrial and marine geomorphology applications and it is important that, in developing the science and application of marine geomorphometry, we build on the lessons learned from terrestrial studies. We note, however, that not all terrestrial solutions can be adopted by marine geomorphometric studies since the dynamic, four- dimensional nature of the marine environment causes its own issues, boosting the need for a dedicated scientific effort in marine geomorphometry. This contribution offers the first comprehensive review of marine geomorphometry to date. It addresses all the five main steps of geomorphometry, from data collection to the application of terrain attributes and features. We focus on how these steps are relevant to marine geomorphometry and also highlight differences from terrestrial geomorphometry. We conclude with recommendations and reflections on the future of marine geomorphometry.peer-reviewe
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