Hydrologic Terrain Processing Using Parallel Computing

Abstract: Topography in the form of Digital Elevation Models (DEMs), is widely used to derive information for the modeling of hydrologic processes. Hydrologic terrain analysis augments the information content of digital elevation data by removing spurious pits, deriving a structured flow field, and calculating surfaces of hydrologic information derived from the flow field. The increasing availability of large terrain datasets with very small ground sample distance (GSD) poses a challenge for existing algorithms that process terrain data to extract this hydrologic information. This paper will describe a parallel algorithm that has been developed to enhance hydrologic terrain pre-processing so that larger datasets can be more efficiently computed. This paper describes a Message Passing Interface (MPI) parallel implementation for Pit Removal. This key functionality is used within the Terrain Analysis Using Digital Elevation Models (TauDEM) package to remove spurious elevation depressions that are an artifact of the raster representation of the terrain. The parallel algorithm works by decomposing the domain into stripes or tiles where each tile is processed by a separate processor. This method also reduces the memory requirements of each processor so that larger size grids can be processed. The parallel pit removal algorithm is adapted from the method of Planchon and Darboux that starts from a large elevation then iteratively scans the grid, lowering each grid cell to the maximum of the original elevation or the lowest neighbor. The MPI implementation reconcile

Evaluating hydrology preservation of simplified terrain representations

We present an error metric based on the potential energy of water flow to evaluate the quality of lossy terrain simplification algorithms. Typically, terrain compression algorithms seek to minimize RMS (root mean square) and maximum error. These metrics fail to capture whether a reconstructed terrain preserves the drainage network. A quantitative measurement of how accurately a drainage network captures the hydrology is important for determining the effectiveness of a terrain simplification technique. Having a measurement for testing and comparing different models has the potential to be widely used in numerous applications (flood prevention, erosion measurement, pollutant propagation, etc). In this paper, we transfer the drainage network computed on reconstructed geometry onto the original uncompressed terrain and use our error metric to measure the level of error created by the simplification. We also present a novel terrain simplification algorithm based on the compression of hydrology features. This method and other terrain compression schemes are then compared using our new metric

Efficient Implicit Parallel Patterns for Geographic Information System

International audienceWith the data growth, the need to parallelize treatments become crucial in numerous domains. But for non-specialists it is still difficult to tackle parallelism technicalities as data distribution, communications or load balancing. For the geoscience domain we propose a solution based on implicit parallel patterns. These patterns are abstract models for a class of algorithms which can be customized and automatically transformed in a parallel execution. In this paper, we describe a pattern for stencil computation and a novel pattern dealing with computation following a pre-defined order. They are particularly used in geosciences and we illustrate them with the flow direction and the flow accumulation computations

Antarctic Peninsula glaciation patterns set by landscape evolution and dynamic topography

The dimensions of past ice sheets provide a record of palaeoclimate but depend on underlying topography, which evolves over geological timescales by tectonic uplift and erosional downcutting. Erosion during the Pleistocene epoch (2,580 to 11.650 thousand years ago) reduced glacier extent in some locations even as climate cooled, but whether other non-climatic influences impacted the glacial–geological record is poorly known. The Antarctic Peninsula provides an opportunity to examine this issue because of its long glacial history and preservation of remnants of a low-relief pre-glacial land surface. Here we reconstructed both palaeo-surface topography and long-wavelength variations of surface uplift for the Antarctic Peninsula by using inverse analysis that assimilates local topographic remnants with the branching structures of entire modern drainage networks. We found that the Antarctic Peninsula rose tectonically by up to 1.5 km due to dynamical support from the mantle. Glaciological models using the current climate and our palaeotopography show greatly reduced ice extent in the northern Antarctic Peninsula compared with modern, indicating that the onset of glaciation identified at offshore sites reflects tectonic uplift of the topography rather than climatic cooling. In the southern Antarctic Peninsula, however, we suggest the low-relief pre-glacial landscape supported a considerably greater ice volume than the modern mountainous topography, illustrating the influence of erosional sculpting on glaciation patterns

Methodology for the solution of massive tasks in GIS

Disertační práce se zabývá problematikou řešení masivních úloh v GIS. Tyto úlohy zpracovávají geografická data velkých objemů a různých formátů. Práce popisuje teoretický rozbor složitosti úloh a možnosti optimalizace dílčích procesů, které vedou k přijatelnému řešení. Zamýšlí se nad možností využití paralelismu v GIS, čímž lze zrychlit zpracování velkého objemu geodat. Navrhuje také způsob optimalizace procesů prostřednictvím algoritmu, který stanoví počet nutných prostředků k úspěšnému vyřešení úlohy v zadaném čase a k přiřazení procesů těmto prostředkům. Dále je zde navržen algoritmus pro optimalizaci při přípravě dat rozsáhlých GIS projektů. Algoritmy byly ověřeny v rámci výzkumného projektu, jehož cílem byla analýza povrchů terénu nad plynovody na území ČR vyjma dvou krajů. Hlavní metodou analýzy byla klasifikace obrazu ortofota, která byla dále zpřesněná filtrací z vrstev ZABAGED. Proto se práce zabývá i možnostmi zpřesnění výsledků klasifikace obrazu s využitím nástrojů GIS a stanovením chybovosti výsledků analýzy. Výstupy analýzy jsou nyní využívány pro strategické plánování údržby a rozvoje plynárenských zařízení v ČR. Výsledky práce mají obecný význam pro řešení stejné třídy úloh v GIS.This doctoral thesis deals with the issue of solving massive tasks in GIS. These tasks process large volumes of geographic data with different formats. The thesis describes a theoretical analysis of the complexity of tasks and the possibilities to optimize sub-processes which lead to an acceptable solution. It considers the possibility of using parallelism in GIS, which leads to an acceleration in the processing of large volumes of geographic data. It also proposes a method for the optimization of processes through an algorithm which determines the number of means necessary for the successful solution of a task at a specified time and assigns processes to these means. Additionally, there is a proposed algorithm for the optimization of the preparation of data for extensive GIS projects. The algorithms have been validated by the results of a research project, the aim of which was to analyse the terrain surface above a gas line in the Czech Republic. The primary method of analysis was the classification of an orthophoto image, which was further refined through filtration using the ZABAGED layers. Therefore, the thesis deals with the possibility of improving the results of image classification using GIS instruments as well as dealing with the determination of the error rate in analysis results. The results of the analysis are now used for the strategic planning of maintenance and the development of gas facilities in the Czech Republic. The results of the work have general importance regarding the performance of other operations of the same class in GIS.

IPH-Hydro Tools : uma ferramenta open source para determinação de informações topológicas em bacias hidrográficas integrada a um ambiente SIG

Watershed delineation, drainage network generation and determination of river hydraulic characteristics are important issues in hydrological sciences. In gene- ral, this information can be obtained from Digital Elevation Models (DEM) processing within GIS commercial softwares, such as ArcGIS and IDRISI. On the other hand, the use of open source GIS tools has increased significantly, and their advantages include free distribution, continuous development by user communities and full customization for specific requirements. Herein, we present the IPH-Hydro Tools, an open source tool coupled to MapWindow GIS software designed for watershed topology acquisition, including preprocessing steps in hydrological models such as MGB-IPH. In addition, several tests were carried out assessing the performance and applicability of the developed tool, given by a comparison with available GIS packages (ArcGIS, IDRISI, WhiteBox) for similar purposes. The IPH-Hydro Tools provided satisfactory results on tested applications, allowing for better drainage network and less processing time for catchment delineation. Regarding its limitations, the developed tool was incompatible with huge terrain data and showed some difficulties to represent drainage networks in extensive flat areas, which can occur in reservoirs and large riversA delimitação de bacias hidrográficas, geração da rede de drenagem e determinação de características hidráulicas de um rio de interesse são partes importantes de estudos na área de hidrologia. Atualmente muitas dessas informações são obtidas com o processamento de modelos digitais de elevação (MDEs) em sof- twares comerciais de SIG, como o ArcGIS e o IDRISI. Por outro lado, pacotes de SIG para uso livre, ou seja, gratuitos e de código aberto, têm aumentado significativamente nos últimos anos, e as vantagens desses pacotes incluem ampla distribuição e customização, desenvolvimento continuado pela comunidade de usuários e atendimento a necessidades específicas. Este trabalho apresenta o pacote livre (open-source) denominado IPH-Hydro Tools, um conjunto de ferramentas acoplado ao software livre MapWindow GIS criado para facilitar a aquisição de informações topológicas em bacias hidrográficas, bem como realização de etapas de pré-processamento em modelos hidrológicos a exemplo do MGB-IPH. Para avaliar a aplicabilidade e o desempenho da ferramenta desenvolvida foram realizados testes específicos, através da comparação dos resultados do IPH-Hydro Tools em relação a outros pacotes de SIG (ArcGIS, IDRISI, WhiteBox) disponíveis para esta finalidade. O IPH-Hydro Tools apresentou qualidade de rede de drenagem geralmente superior aos demais pacotes e menor tempo de processamento necessário para delimitação de bacias, apesar de algumas limitações como incompatibilidade em relação a matrizes muito grandes e dificuldade na representação da rede de drenagem em áreas extensas de mesma cota, a exemplo de reservatórios e rios muito largos