Adaptive DTM generalization methods for tangible GIS applications     

Maria Papadogiorgaki  Panagiotis Partsinevelos 《Earth Science Informatics》2017,10(4):483-494

Several international studies attempt to construct tangible GIS systems, forming real 3D surfaces using a large number of mechanical parts along a matrix formation. Most of these attempts suffer in cost, accuracy, resolution and/or speed. In order to facilitate data handling in GIS tangible systems, the generalization process becomes crucial, accommodating compression, visualization and comprehension of spatial data under various scales. Under this perspective, the main objective of the proposed adaptive generalization approach is to provide optimized representation of 3D digital terrain models with minimum loss of information, serving specific applications. That is, to minimize the number of pixels in a raster dataset used to define a DTM, while reserving surface information and enhancing the important semantic features. To this aim, this paper presents specific computationally efficient surface generalization approaches, which can be incorporated in applications of tangible GIS systems, due to their low processing time, facilitating real-time results. The research methods developed and tested include adaptive variations of a) the Douglas-Peucker line simplification algorithm in 3D data and b) the spatial Laplace filter that estimates the significance of each node, based on its nearest neighbors. The proposed strategy also dynamically incorporates topology and semantic restraints, in order to preserve important information and depict it with variable detail level, according to the application at hand. The algorithms are evaluated on their accuracy for a specific wildfire application and for different reduction levels in two different types of terrain data. They are also compared to their original-basic implementations in terms of performance.  相似文献   

Contribution to the identification of the sea intrusion mechanism of brackish karst springs     

Athanasios Maramathas  Panagiotis Pergialiotis  Ioannis Gialamas 《Hydrogeology Journal》2006,14(5):657-662

A method of identifying the dominant hydrodynamic sea-intrusion mechanism of brackish karst springs is presented. A karst spring becomes brackish when tubes, which bring the freshwater to the spring (freshwater discharge), intersect other tubes that come from the sea and bring saltwater to the freshwater tubes (saltwater discharge) when the saltwater pressure at the intersection is higher than the freshwater pressure. There are two potential seawater intrusion mechanisms. The first one is the difference between the freshwater density and the seawater density, and the second is the venturi effect. Both mechanisms are present but it is a matter of great significance to know which mechanism dominates. In order to find out the dominant mechanism, the seawater discharge versus the freshwater discharge was charted using the MODKARST model, which estimates these discharges. The model determines how the freshwater discharge affects the saltwater discharge estimating thereby the dominant seawater intrusion mechanism. Application was made to the “Almiros” and “Makaria” springs in Greece.

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Resumen Se presenta un método para identificar el mecanismo hidrodinámico dominante de la intrusión marina en manantiales salobres cársticos. Un manantial cárstico se vuelve salobre cuando los conductos, que suministran agua dulce al manantial (caudal de agua dulce), interceptan a otros conductos provenientes del mar que traen agua salada a este (caudal de agua salada), bajo la condición que la presión del agua salada en la intersección es mayor que la del agua dulce. Hay dos mecanismos potenciales de intrusión salina. El primero es la diferencia de densidades entre agua salada y agua dulce, mientras que el segundo es el efecto venturi. Ambos mecanismos están presentes en cualquier caso, sin embargo es de gran importancia establecer cual de ellos predomina. Con el fin de hallar el mecanismo dominante se tabularon los valores de caudal de agua salada versus el de agua dulce. Lo anterior fue posible mediante el uso del modelo MODKARST, el cual estima estos caudales. A partir de esta tabla se puede examinar como el caudal de agua dulce afecta al de agua salada, estimando como resultado de lo anterior el mecanismo dominante en la intrusión marina. Esto se aplicó a los manantiales “Almiros” y “Makaria” en Grecia.

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Résumé On présente une méthode pour déterminer le mécanisme hydraulique dominant de l’intrusion de l’eau salée marine dans le cas des émergences karstiques saumatres. Une émergence karstique devienne saumatre á l’intersection des conduites de l’eau douce avec des autres conduits qui apportent l’eau salée de la mer. Ce processus est possible si la pression de l’eau salée dépasse la pression de l’eau douce. Il y a deux mécanismes potentiels de l’intrusion de l’eau salée. A la base du premier mécanisme se trouve la différence entre les densités de l’eau douce et de l’eau salée pendant que dans le deuxième mécanisme il s’agit de phénomène Venturi. Afin de trouver le mécanisme dominant on a cartographié avec le modèle MODKARST le rapport entre les décharges de l’eau douces et respectivement de l’eau salée. A partir de la carte résultée on peut estimer comment la décharge de l’eau douce influence celle de l’eau salée en estimant en même temps le mécanisme dominat de l’eau salée. On a appliqué la méthode dans le cas des émergences d’Almiros et Makaria de la Grèce.

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Improving Properties of Sand Using Epoxy Resin and Electrokinetics     

Costas A. Anagnostopoulos  Panagiotis Kandiliotis  Malvina Lola  Sarafianos Karavatos 《Geotechnical and Geological Engineering》2014,32(4):859-872

The use of new materials for soil strengthening is crucial for geotechnical engineering, especially in foundation construction. The main objective of this study was to investigate the potential use of two-component water-soluble epoxy resin to improve the physical and mechanical properties of medium sand, because the efficacy of these resins on soil strengthening has not yet been properly investigated. The experiments were conducted using resins with different epoxy resin-to-water ratios. The results of this study indicate that the epoxy resins improve the physical and mechanical properties of the sand significantly, and if successfully grouted into a formation, the resins could provide a suitable solution for the stabilization of the foundation material. In separate experiments, electroosmotic treatment of sand/resin mixtures was conducted with the aim of identifying the effectiveness of electro kinetic method on the early strength development of sand/resin mixtures. From the results it was observed that the electroosmotically treated specimens appeared to have much greater strength enhancement than the one of the untreated specimens.  相似文献   

A hybrid optimization scheme for self-potential measurements due to multiple sheet-like bodies in arbitrary 2D resistivity distributions     

Iraklis Giannakis  Panagiotis Tsourlos  Costas Papazachos  George Vargemezis  Antonios Giannopoulos  Nikos Papadopoulos  Fabio Tosti  Amir Alani 《Geophysical Prospecting》2019,67(7):1948-1964

Self-potential is a passive geophysical method that can be applied in a straightforward manner with minimum requirements in the field. Nonetheless, interpretation of self-potential data is particularly challenging due to the inherited non-uniqueness present in all potential methods. Incorporating information regarding the target of interest can facilitate interpretation and increase the reliability of the final output. In the current paper, a novel method for detecting multiple sheet-like targets is presented. A numerical framework is initially described that simulates sheet-like bodies in an arbitrary 2D resistivity distribution. A scattered field formulation based on finite differences is employed that allows the edges of the sheet to be independent of the grid geometry. A novel analytical solution for two-layered models is derived and subsequently used to validate the accuracy of the proposed numerical scheme. Lastly, a hybrid optimization is proposed that couples linear least-squares with particle-swarm optimization in order to effectively locate the edges of multiple sheet-like bodies. Through numerical and real data, it is proven that the hybrid optimization overcomes local minimal that occurs in complex resistivity distributions and converges substantially faster compared to traditional particle-swarm optimization.  相似文献   

A new dynamical spectrum for galactic potentials     

G.I. Karanis  N.D. Caranicolas 《Astronomische Nachrichten》2002,323(1):3-11

We investigate the properties of motion, using the distribution of the values of a new dynamical parameter, in two different galactic potentials. The first is a potential made up of harmonic oscillators while the second is a logarithmic potential. We call the distribution functions of the new parameter the S(r) dynamical spectrum. A comparison between the spectrum of stretching numbers S(α) and the new spectrum is made. The results of our numerical calculations suggest that the S(r) spectrum is a better discriminant between different types of orbits while requiring considerable less computation time. An application of the new dynamical spectrum to barred galaxy models is also presented.  相似文献   

Sand,hearths, lithics and a bit of bioturbation: Site formation processes at Umhlatuzana rockshelter,South Africa     

Irini Sifogeorgaki  Hans Huisman  Panagiotis Karkanas  Viola C. Schmid  Gerrit L. Dusseldorp 《Geoarchaeology》2024,39(3):212-237

Umhlatuzana rockshelter is known for its continuous record of Middle and Later Stone Age lithic assemblages. This study presents multiproxy geoarchaeological data (micromorphology, X-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy) to reconstruct the depositional and post-depositional history of the site. Although the Stone Age deposits macroscopically appear homogeneous, micromorphological analysis reveals the existence of primary, unaltered depositional microlayering throughout the sequence. Sediments related to combustion activities on-site are observed in both the Holocene and Pleistocene deposits. Post-depositional geochemical alterations result in the formation of several phosphatic minerals that significantly affect the site's preservation conditions. One of those is vashegyite, a rare magnesium phosphate mineral related to acidic and moist sedimentary environments. Bioturbation features are prominent at the microscale, but sediment mixing does not seem to affect the vertical distribution of the artifacts. The observation of horizontal microlayering in both the Pleistocene and Holocene illuminates the dominant mechanism of sedimentation throughout the site's 70,000-year occupational history. It moreover shows that the lithics can be analysed as coherent assemblages.  相似文献