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mapping functions Driven Robust Retinal Vessel Segmentation via Training Patches

IEEE ACCESS 2018年 6卷 61973-61982页

作者： Xia, Haiying Jiang, Frank Deng, Shuaifei Xin, Jing Doss, Robin Guangxi Normal Univ Coll Elect Engn Guilin 541000 Peoples R China Guilin Univ Elect Technol Guilin 541000 Peoples R China Guilin Univ Aerosp Technol Guilin 541004 Peoples R China Deakin Univ Sch Informat Technol Geelong Vic 3125 Australia Shanghai Micro Elect Equipment Co Ltd Shanghai 201203 Peoples R China Xian Univ Technol Sch Automat & Informat Engn Xian 710054 Shaanxi Peoples R China

Vein occlusions and diabetic retinopathy are two of many retinal pathologies affecting the retina. Understanding robust vessel segmentation of fundus images is of vital importance for improving the diagnosis results of these diseases. This paper proposes a novel approach for computing the minimum distance for each test patch via the distance comparison within the test patch and cluster centers. The numerous patches are calculated using manual segmentations through the K-means algorithm. We demonstrate the efficiency of learning the simple pattern from each cluster;meanwhile, the mapping function for each cluster is determined by the patches in the training images and their corresponding manual segmentation patches. Two publicly recognized benchmark data sets, namely DRIVE and STARE, are used in our experimental validation. Experimental results show that the proposed approach outperforms conventional methods for vessel segmentation problems validated via public benchmark data sets, i.e., DRIVE and STARE.

关键词： Fundus images mapping functions vessel segmentation

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mapping functions and data redistribution for parallel files

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JOURNAL OF SUPERCOMPUTING 2008年第3期46卷 213-236页

作者： Isaila, Florin Tichy, Walter F. Univ Carlos III Madrid Dept Comp Sci Madrid Spain Univ Karlsruhe Dept Comp Sci Karlsruhe Germany

Data distribution in memory or on disks is an important factor influencing the performance of parallel applications. On the other hand, programs or systems, like a parallel file system, frequently redistribute data between memory and disks. This paper presents a generalization of previous approaches of the redistribution problem. We introduce algorithms for mapping between two arbitrary distributions of a data set. The algorithms are optimized for multidimensional array partitions. We motivate our approach and present potential utilizations. The paper also presents a case study, the employment of mapping functions, and redistribution algorithms in a parallel file system.

关键词： Parallel file systems Parallel I/O Noncontiguous I/O Multi-dimensional array redistribution mapping functions

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mapping functions in Health-Related Quality of Life: mapping from Two Cancer-Specific Health-Related Quality-of-Life Instruments to EQ-5D-3L

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MEDICAL DECISION MAKING 2015年第7期35卷 912-926页

作者： Young, Tracey A. Mukuria, Clara Rowen, Donna Brazier, John E. Longworth, Louise Univ Sheffield Sch Hlth & Related Res ScHARR Sheffield S1 4DA S Yorkshire England Brunel Univ HERG Uxbridge Middx England

Background. Clinical trials in cancer frequently include cancer-specific measures of health but not preference-based measures such as the EQ-5D that are suitable for economic evaluation. mapping functions have been developed to predict EQ-5D values from these measures, but there is considerable uncertainty about the most appropriate model to use, and many existing models are poor at predicting EQ-5D values. This study aims to investigate a range of potential models to develop mapping functions from 2 widely used cancer-specific measures (FACT-G and EORTC-QLQ-C30) and to identify the best model. Methods. mapping models are fitted to predict EQ-5D-3L values using ordinary least squares (OLS), tobit, 2-part models, splining, and to EQ-5D item-level responses using response mapping from the FACT-G and QLQ-C30. A variety of model specifications are estimated. Model performance and predictive ability are compared. Analysis is based on 530 patients with various cancers for the FACT-G and 771 patients with multiple myeloma, breast cancer, and lung cancer for the QLQ-C30. Results. For FACT-G, OLS models most accurately predict mean EQ-5D values with the best predicting model using FACT-G items with similar results using tobit. Response mapping has low predictive ability. In contrast, for the QLQ-C30, response mapping has the most accurate predictions using QLQ-C30 dimensions. The QLQ-C30 has better predicted EQ-5D values across the range of possible values;however, few respondents in the FACT-G data set have low EQ-5D values, which reduces the accuracy at the severe end. Conclusions. OLS and tobit mapping functions perform well for both instruments. Response mapping gives the best model predictions for QLQ-C30. The generalizability of the FACT-G mapping function is limited to populations in moderate to good health.

关键词： health-related quality of life mapping functions cancer EQ-5D-3L FACT-G EORTC-QLQ-C30

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Planar Electromagnetic Bandgap Structures Based on Polar Curves and mapping functions

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2010年第3期58卷 790-797页

作者： Mulenga, Charity B. Flint, James A. Univ Loughborough Dept Elect & Elect Engn Loughborough LE11 3TU Leics England

A type of electromagnetic bandgap structure is described that is easily parameterized and can produce a range of square and spiral geometries. Individual electromagnetic bandgap (EBG) geometries are defined on a cell-by-cell basis in terms of their convolution factor, which defines the extent to which the elements are interleaved and controls the coupling slot length between adjacent elements. Polar equations are used to define the slot locus which also incorporate a transformation which ensures the slot extends into the corners of the square unit cell and hence extends the maximum slot length achievable. The electromagnetic properties of the so-called polar EBG are evaluated by means of numerical simulation and measurements and dispersion diagrams are presented. Finally, the performance is compared with other similar miniaturized EBG cell geometries. It is shown that the polar EBG has better angular stability than the equivalent square patch design and is comparable in terms of performance to other low frequency EBG elements. At the same time it retains the ability to fine tune the response by adjusting k.

关键词： Electromagnetic bandgap (EBG) mapping functions metamaterials polar curves

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Assessment of troposphere mapping functions using three-dimensional ray-tracing

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GPS SOLUTIONS 2014年第3期18卷 345-354页

作者： Urquhart, Landon Nievinski, Felipe G. Santos, Marcelo C. Univ New Brunswick Dept Geodesy & Geomat Engn Fredericton NB Canada Univ Colorado Dept Aerosp Engn Sci Boulder CO 80309 USA

The troposphere delay is an important source of error for precise GNSS positioning due to its high correlation with the station height parameter. It has been demonstrated that errors in mapping functions can cause sub-annual biases as well as affect the repeatability of GNSS solutions, which is a particular concern for geophysical studies. Three-dimensional ray-tracing through numerical weather models (NWM) is an excellent approach for capturing the directional and daily variation of the tropospheric delay. Due to computational complexity, its use for positioning purposes is limited, but it is an excellent tool for evaluating current state-of-the-art mapping functions used for geodetic positioning. Many mapping functions have been recommended in the past such as the Niell mapping Function (NMF), Vienna mapping Function 1 (VMF1), and the Global mapping Function (GMF), which have been adopted by most IGS analysis centers. A new Global Pressure Temperature model (GPT2) has also been developed, which has been shown to improve upon the original atmospheric model used for the GMF. Although the mapping functions mentioned above use the same functional formulation, they vary in terms of their atmospheric source and calibration approach. A homogeneous data set of three-dimensional ray-traced delays is used to evaluate all components of the mapping functions, including their underlying functional formulation, calibration, and compression method. Additionally, an alternative representation of the VMF1 is generated using the same atmospheric source as the truth data set to evaluate the differences in ray-tracing methods and their effect on the end mapping function. The results of this investigation continue to support the use of the VMF1 as the mapping function of choice when geodetic parameters are of interest. Further support for the GPT2 and GMF as reliable back-ups when the VMF1 is not available was found due to their high consistency with the NWM-derived mapping function.

关键词： Troposphere Numerical weather models mapping functions

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Laminar flow calculations in ducts of complex shapes using mapping functions and decomposition of domains

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MATHEMATICS AND COMPUTERS IN SIMULATION 2000年第1期52卷 21-39页

作者： Normandin, M Clermont, JR Mahmoud, A Univ Grenoble 1 CNRS UMR 5520 Lab Rheol F-38041 Grenoble 9 France Inst Natl Polytech Grenoble F-38041 Grenoble France

The method presented in this paper, based on geometrical considerations, concerns the use of unknown transformations and decomposition of domains for computation of fully-developed flows in ducts of complex shape. The approach involves local one-to-one transformations of sub-domains of the physical two-dimensional domain into simple mapped domains used for computation, where a rectangular mesh can be defined. The formulation allows direct calculation of velocity contour values in flow regions close to the boundaries, avoiding problems that may arise from geometrical singularities in shape of the physical domain. Application of the method are given for different types of ducts with fluids obeying various constitutive equations. The set of governing equations is solved by the means of the Levenberg-Marquardt optimization algorithm. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

关键词： mapping functions laminar flow decomposition of domain

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Systematic errors of mapping functions which are based on the VMF1 concept

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GPS SOLUTIONS 2015年第2期19卷 277-286页

作者： Zus, Florian Dick, Galina Dousa, Jan Wickert, Jens Deutsch GeoForschungsZentrum GFZ Helmholtz Zentrum Potsdam GPS Galileo Earth Observat D-14473 Potsdam Germany New Technol Informat Soc NTIS Res Inst Geodesy Topog & Cartog Zdiby 25066 Czech Republic

Precise global navigation satellite system (GNSS) positioning requires an accurate mapping function (MF) to model the tropospheric delay. To date, the most accurate MF is the Vienna mapping function 1 (VMF1). It utilizes data from a numerical weather model and therefore captures the short-term variability of the atmosphere. Still, the VMF1, or any other MF that is based on the VMF1 concept, is a parameterized mapping approach, and this means that it is tuned for specific elevation angles, station heights, and orbital altitudes. In this study, we analyze the systematic errors caused by such tuning on a global scale. We find that, in particular, the parameterization of the station height dependency is a major concern regarding the application in complex terrain or airborne applications. At this time, we do not provide an improved parameterized mapping approach to mitigate the systematic errors but instead we propose a (ultra-) rapid direct mapping approach, the so-called Potsdam mapping factors (PMFs). Since for any station-satellite link the ratio of the tropospheric delay in the slant and zenith direction is computed directly, the PMFs effectively eliminate the systematic errors.

关键词： Precise positioning Numerical weather model mapping functions Rapid direct mapping

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Performance evaluation of different troposphere delay models and mapping functions

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MEASUREMENT 2013年第2期46卷 928-937页

作者： Tuka, A. El-Mowafy, A. Curtin Univ Technol Dept Spatial Sci Perth WA 6845 Australia

Tropospheric delay is a major error source in positioning by Global Navigation Satellite Systems (GNSSs). System users often apply one of the available troposphere models without giving sufficient background on their performance. In this study, the performance of different known hydrostatic and wet troposphere delay models and mapping functions are internally and externally compared and analysed at selected sites around the globe. International GNSS Service (IGS) products were used as a reference. The best performing models are presented. Results showed that small discrepancies are present between different models. All models perform significantly better at the mid-latitudes than at the Equator. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

关键词： Troposphere delay GNSS mapping functions Wet delay Hydrostatic delay

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Ionospheric mapping functions based on electron density fields

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GPS SOLUTIONS 2017年第3期21卷 873-885页

作者： Zus, Florian Deng, Zhiguo Heise, Stefan Wickert, Jens Deutsch GeoForschungsZentrum GFZ Helmholtz Zentrum Potsdam GPS Galileo Earth Observat D-14473 Potsdam Germany

We develop an ionospheric mapping function (MF) for the global navigation satellite system (GNSS) which is based on the electron density field derived from the international reference ionosphere (IRI). The station specific MF utilizes a look-up table which contains a set of ray-traced ionospheric phase advances and code delays. Hence, unlike the simple MFs that are currently in use, the developed MF depends on the time, location, elevation and azimuth angle. Ray-bending is taken into account, which implies that the MF depends on the carrier frequency as well. The frequency dependency of the MF can be readily used to examine higher-order ionospheric effects due to ray-bending. We compare the proposed MF with the so-called single-layer model MF and find significant differences in particular around the equatorial anomaly. In so far as the proposed MF is based on a realistic electron density field (IRI), our comparison shows the potential error of the single-layer model MF in practice. We conclude that the developed MF concept might be valuable in the GNSS total electron content estimation. The frequency dependency of the MF can be used to mitigate higher-order ionospheric effects.

关键词： mapping functions International reference ionosphere Higher-order ionospheric effects

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VMF3/GPT3: refined discrete and empirical troposphere mapping functions

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JOURNAL OF GEODESY 2018年第4期92卷 349-360页

作者： Landskron, Daniel Boehm, Johannes Tech Univ Wien Vienna Austria

Incorrect modeling of troposphere delays is one of the major error sources for space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). Over the years, many approaches have been devised which aim at mapping the delay of radio waves from zenith direction down to the observed elevation angle, so-called mapping functions. This paper contains a new approach intended to refine the currently most important discrete mapping function, the Vienna mapping functions 1 (VMF1), which is successively referred to as Vienna mapping functions 3 (VMF3). It is designed in such a way as to eliminate shortcomings in the empirical coefficients b and c and in the tuning for the specific elevation angle of . Ray-traced delays of the ray-tracer RADIATE serve as the basis for the calculation of new mapping function coefficients. Comparisons of modeled slant delays demonstrate the ability of VMF3 to approximate the underlying ray-traced delays more accurately than VMF1 does, in particular at low elevation angles. In other words, when requiring highest precision, VMF3 is to be preferable to VMF1. Aside from revising the discrete form of mapping functions, we also present a new empirical model named Global Pressure and Temperature 3 (GPT3) on a as well as a global grid, which is generally based on the same data. Its main components are hydrostatic and wet empirical mapping function coefficients derived from special averaging techniques of the respective (discrete) VMF3 data. In addition, GPT3 also contains a set of meteorological quantities which are adopted as they stand from their predecessor, Global Pressure and Temperature 2 wet. Thus, GPT3 represents a very comprehensive troposphere model which can be used for a series of geodetic as well as meteorological and climatological purposes and is fully consistent with VMF3.

关键词： VLBI GNSS Troposphere mapping functions Horizontal gradients

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