Set Of Control Points Research Articles

Evaluation of RBFs for volume data interpolation in CFD

SUMMARYA greedy method for choosing an optimum reduced set of control points is integrated with RBF interpolation and evaluated for the purpose of interpolating large‐volume data sets in CFD. Given a function defined at a set of points, the greedy method selects a small subset of these points that is sufficient to keep the interpolation error at all the remaining points below a chosen bound. This is equivalent to a type of data compression and would have useful storage, post‐processing, and computational applications in CFD. To test the method in terms of both the point selection scheme and the suitability of reduced control point volume interpolation, a trial application of the interpolation to velocity fields in CFD volume meshes is considered. To optimise the point selection process, and attempt to be able to capture multiple length scales, a variable support radius formulation has also been included. Structured and unstructured mesh cases are considered for aerofoils, a wing case and a wing‐body case. For smooth volume functions, the method is shown to work well, producing accurate velocity interpolations using a very small number of the cells in the mesh. For general complex fields including large gradients, the method is still shown to be effective, although large gradients require more interpolation points to be used.Copyright © 2013 John Wiley & Sons, Ltd.

An Alternative Methodology to Represent B-spline Surface for Applications in Virtual Reality Environment

AbstractB-spline representation is one of the main methods for free-form surface modeling and has become the standard for CAD systems. However, in Virtual Reality (VR) environment, when a B-spline surface deforms, the blending functions need to be continuously computed. The high computational cost of continuously calculating the blending functions for merging, collision detection and physics-based deformation system, while the model is deforming, restricts the use of B-spline representation in a VR environment. This paper presents an alternative methodology to represent B-spline surface patches for an interactive VR environment. A uniformly discretized B-spline surface patch can be represented by a set of control points and two precalculated B-spline blending matrices. The proposed technique exploits the fact that these B-spline blending matrices are independent of the position of control points and therefore can be pre-calculated. The blending matrices enable the algorithm to merge B-spline surface patch...

Handling Low-Density LiDAR Data: Calculating the Heights of Civil Constructions and the Accuracy Expected

During the last years, in many developed countries, administrations and private companies have devoted considerable amounts of money to obtain mapping data using airborne LiDAR. For many civil activities, we can take advantage of it, since those data are available with no cost. Some important questions arise: Are those data good enough to be used for determining the heights of the civil constructions with the accuracy we need in some civil work? What accuracy can we expect when using low-density LiDAR data (0.5 pts/m2)? In order to answer those questions, we have developed a specific methodology based on establishing a set of control points on the top of several constructions and calculating the elevation of each one using postprocessing GPS. Those results have been taken as correct values and the comparison between those values and the elevations obtained, assigning values to the control points by the interpolation of the LiDAR dataset, has been carried out. This paper shows the results obtained using low-density airborne LiDAR data and the accuracy obtained. Results have shown that LiDAR can be accurate enough (10–25 cm) to determine the height of civil constructions and apply those data in many civil engineering activities.

수학적 모형화 기법이 GPS 기준점 측량 정확도 표현에 미치는 영향

GPS 기준점 측량은 관측과 데이터 처리를 통해 측지계에 대한 물리적인 표지의 위치를 목표 정확도 범위 이내로 결정하기 위해 실시하며, 이러한 이유로 측량 정확도를 실제와 유사하게 표현하는 것이 매우 중요한 문제이다. 망조정을 통해 산정되는 기준점 성과의 정확도는 사용되는 수학적 모형에 민감한 영향을 받는 추정좌표의 분산-공분산 행렬에 의해 정량적으로 표현된다. 본 연구는 GPS 망조정에 사용되는 함수모형과 통계모형이 기준점 위치 추정과 정확도 표현에 미치는 영향을 연구하여 향후 정확도 표현의 표준화를 위한 기초자료 확보를 위해 실시하였다. 이를 위하여 단일기선해석 다중세션 망조정 이론과 절차와 방법을 실제 관측데이터 처리를 통한 수치적 분석을 병행한 연구를 수행 하였다. 그 결과 절대정확도와 상대정확도를 보다 현실적으로 반영하여 표현하기 위해서는 잔존하는 관측오차의 모형화가 가능한 경험적 통계모형을 사용하는 다점가중제약조정이 GPS 기준점 성과산정을 위한 수학적 모형으로 보다 타당한 것으로 분석되었다. The objective of GPS control surveying is ultimately to determine coordinate sets of control points within targeted accuracy through a series of observations and network adjustments. To this end, it is of equivalent importance for the accuracy of these coordinates to be realistically represented by using an appropriate method. The accuracy representation can be quantitively made by the variance-covariance matrices of the estimates, of which features are sensitive to the mathematical models used in the adjustment. This paper deals with impact of functional and stochastic modeling techniques into the accuracy representation of the GPS control surveying with a view of gaining background for its standardization. In order to achieve this goal, mathematical theory and procedure of the single-baseline based multi-session adjustment has been rigorously reviewed together with numerical analysis through processing real world data. Based on this study, it was possible to draw a conclusion that weighted-constrained adjustment with the empirical stochastic model was among the best scheme to more realistically describe both of the absolute and relative accuracies of the GPS surveying results.

Triangular Bézier surface patches in modeling shape of boundary geometry for potential problems in 3D

This paper presents a new boundary shape representation for 3D boundary value problems based on parametric triangular Bézier surface patches. Formed by the surface patches, the graphical representation of the boundary is directly incorporated into the formula of parametric integral equation system (PIES). This allows us to eliminate the need for both boundary and domain discretizations. The possibility of eliminating the discretization of the boundary and the domain in PIES significantly reduces the number of input data necessary to define the boundary. In this case, the boundary is described by a small set of control points of surface patches. Three numerical examples were used to validate the solutions of PIES with analytical and numerical results available in the literature.

Sparse Adaptive Parameterization of Variability in Image Ensembles

This paper introduces a new parameterization of diffeomorphic deformations for the characterization of the variability in image ensembles. Dense diffeomorphic deformations are built by interpolating the motion of a finite set of control points that forms a Hamiltonian flow of self-interacting particles. The proposed approach estimates a template image representative of a given image set, an optimal set of control points that focuses on the most variable parts of the image, and template-to-image registrations that quantify the variability within the image set. The method automatically selects the most relevant control points for the characterization of the image variability and estimates their optimal positions in the template domain. The optimization in position is done during the estimation of the deformations without adding any computational cost at each step of the gradient descent. The selection of the control points is done by adding a L 1 prior to the objective function, which is optimized using the FISTA algorithm.

Dual-layer loudspeaker array for multiple listening zones

A dual-layer array consisting of sixteen small (1″) loudspeakers has been built for simultaneous transmission of audio signals to multiple listeners occupying different regions of the space. The audio signals are filtered through a bank of FIR filters, computed using a Least Mean Squares (LMS) approach with regularization. The plant matrix of the array, representing the transfer functions between the loudspeakers and a set of control points, was measured in the anechoic chamber of the ISVR and was used in the filter matrix calculation. It is shown that the selection of both the number and location of the control points has direct impact on the condition number of the plant matrix, on the frequency response of the digital filters, on the frequency response of the reproduced signals, and on the acoustic radiation pattern of the array. Results are shown for several application cases, which demonstrate also the capability of controlling independently the sound radiation to the front and to the back of the dual-layer array.

The accomplishment of the field of the phased array high intensity focused ultrasound using pseudo-inverse method

In this paper, the two-focused field of phased array intensity focused ultrasound have been accomplished using the pseudo-inverse method. To reducing grating-labs, the elements in array are randomly placed. The forward propagation operator from the surface of the array to the set of control points should be known when we use the pseudo-inverse method to get the excitation vector. Because of the element placing with high-frequency and large-size, the relative positions of element need to be estimated accurately. A method to get the high precision three-dimensional coordinates of the element are proposed and so the excitation vector have been get to accomplish the field of two-focus.

A three-dimensional orientation method for estimating a concave spherical array in phased array high intensity focused ultrasound

The pseudo-inverse matrix method can be used to get complex excitation vector through the forward propagation operator from the surface of the array to the set of control points before the scheduled complex pressure at the control points is formed. The relative positions of the elements in the array should be estimated accurately since the elements are randomly placed with high-frequency and large-size. The high precision three-dimensional coordinates of elements are obtained by ways of comparing phase differences measured and calculated. The ideal distribution of focused sound field validates the precision of this way in which the measured phase differences are regarded as the initial phases of the elements.

SRTM 3" comparison with local information: Two examples at national level in Peru

The access to the high resolution digital terrain models (DEM) generated from the data collected by the Shuttle Radar Topography Mission (SRTM) of NASA is freely available to the public. Consequently it has become a source of topographic information which is of great value to scientists involved in geophysical or geodetic analysis. Despite the efforts of the Consultative Group on International Agricultural Research (CGIAR), to validate and complement the information contained in these DEMs (currently offered as version 4.1), they still need to be checked for their accuracy in certain regions of the planet. In this paper, the vertical accuracy of the SRTM 3" version 4.1 DEM was analyzed in several areas of Peru using two sets of control points: the height of the district capitals (the minor politics units) and the heights of the weather and hydrological stations from the National Meteorology and Hydrology Service (SENAMHI) of Peru. The comparison shows that the height differences are independent of the altitude, latitude and longitude of the evaluated points. They are rather related to the aspect of the terrain and to the way the SRTM data were acquired. It shows that the mean square of the height differences at national level was ±20 m for district capitals and ±25 m for the SENAMHI stations. This is slightly larger than the overall accuracy of the SRTM ±16 m.

Real-time adjustment of transfer function for Fourier volume rendering

Fourier volume rendering (FVR) is a volume rendering method based on the Fourier slice theorem. With an n × n × n volume data, the FVR algorithm requires O(n2 log n) time to generate a result. Because it requires time less than O(n3) does, FVR is preferred for designing a real-time rendering algorithm with a preprocessing step. We improve upon our previous work. We demonstrate that a B-spline is significantly more useful when designing a transfer function. To design an appropriate transfer function with a spline function, additional control points are required. However, the memory space required for the proposed method increases in linear proportion to the number of control points. We show that the set of control points can be clustered into groups, ensuring the memory required is linearly proportional to the number of groups. The proposed technique supports real-time rendering after adjusting the transfer function for FVR.

3D numerical definition with vectors for human smiles

In most of the numerical methods for facial expressions in the literatures, the number of the key controls for animators or robot programmers are too complex and trivial, because what they want are less and critical controls. This study explored varied types of human smiles and extracted proper key factors affecting the smiles. These key factors then were converted into a set of control points which could serve to satisfy the needs for creation of facial expression for 3D animators and be further applied to the face simulation for robots in the future. First, hundreds of human smile pictures were collected and analyzed to identify the key factors for face expression. Then, the factors were converted into a set of control points and sizing parameters calculated proportionally. Finally, two different faces were constructed for validating the parameters via the process of simulating smiles of the same type as the original one.

GPS 측지망 조정을 통한 국가기준점 성과의 상시 산정 체계에 관한 연구

본 논문에서는 지각판 운동 지진과 같은 급격한 지각변동을 고려한 국가기준점의 상시적 성과 산정 체계 수립에 관한 연구를 수행하였다. 이를 위하여 GPS 기준점의 국내 현황 및 최근 국가기준점의 재정비가 이루어진 국외 사례 조사로부터 시사점을 도출하고 GPS 상시관측점으로 이루어진 위성기준점망과 6,900 여점으로 이루어진 단일 GPS 망으로 단순화된 국가기준점의 계층 구조를 제안하였다. 또한, 초고정밀 다중기선해석과 정규방정식의 누적에 의한 연속조정을 통한 단계별 위성기준점의 성과 산정 절차 및 다중 세션 조정에 의한 단일 GPS 기준망의 성과 산정 방안을 제시하였다. 또한, 시험 조정망을 구성하여 조정계산을 실시하고 결과 분석을 통해 상시적 성과산정의 필요성과 제안한 성과산정 방법 및 절차의 타당성 등을 평가하였다. This paper has focused on deriving a GPS based geodetic network adjustment strategy to continuously determine coordinate sets of the national geodetic control points. After domestic literature review on the topic and overseas case studies about countries that recently reformed their geodetic infrastructure have been carried out, a simplified geodetic network consisting of two layers, namely GPS active and passive network, has been proposed to maximize effectiveness of the network adjustment through reducing the number of the passive points. Furthermore, a GPS data processing and network adjustment procedure has been derived to support the continuous management scheme. While a scheme for the active layer adopts a sequential least squares adjustment based on a multi-baseline, that of the passive layer employs a multi-session adjustment technique with respect to 3-dimensional baseline vectors. Finally, experimental adjustment against a network comprising 24 active and 6,900 passive stations has been performed to demonstrate the efficiency and the effectiveness of the proposed method.

Estimation of Thin Ice Thickness From the Advanced Microwave Scanning Radiometer-EOS for Coastal Polynyas in the Chukchi and Beaufort Seas

In this paper, a thin ice thickness algorithm for coastal polynyas in the Chukchi and Beaufort Seas has been attempted which uses the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) 89-GHz brightness temperature data at a 6.25-km resolution. Thermal ice thickness estimated from the Moderate Resolution Imaging Spectroradiometer (MODIS) ice surface temperature data for a set of control points is used in conjunction with the AMSR-E brightness temperature data to develop a regression relationship between the thermal ice thickness and the passive microwave polarization ratio. The MODIS thermal ice thickness has been determined from the calculation of conductive heat flux through the ice-air interface. The relationship is then applied across the polynyas to derive thin ice thickness information at different points. In the development of the algorithm, the MODIS-derived thermal thickness is assumed to be the standard reference. Validation of the algorithm has been carried out using an independent MODIS-derived thermal ice thickness data set. It is observed that the model error is 1.3 cm within the thickness range of 1-10 cm. This method is expected to be useful in high latitudes where in situ observations are sparse.

Assessment of cartographic potential of EgyptSat-1 satellite image (case study in flat areas)

Egypt has launched its first Earth remote sensing satellite EgyptSat-1 in 2007. A series of evaluations of the usefulness and limitations of EgyptSat-1 images for different applications are required. This research is concerned with the investigation of the geometric and cartographic potential of EgyptSat-1 image in order to know to what scale EgyptSat-1 image is suitable for map production and map updating. The geometrical accuracy of rectification of EgyptSat-1 based on non-parametric rectification (polynomial approach and rubber sheeting) has been evaluated. Four methods of rectification have been compared: different orders of 2D polynomials (first-order polynomial, second-order polynomial, third-order polynomial) and rubber sheeting method. Different sets of ground control points (observed with differential global positioning system) have been tested. Several experiments were performed to rectify EgyptSat-1 image using the four rectification methods. For each method, different numbers of ground control points (GCPs) were used starting at 15 points, and then the number was reduced each time till the minimum number of GCPs for each method is reached and with three different GCP distributions. Various issues such as the solutions, feasibility, accuracy, and requirements for control information are addressed. The results show that rubber sheeting followed by third-order polynomial then second-order polynomial then first-order polynomial gives the best root mean square error. Actually, a serious mapping should be based on a satisfying by the theory justified mathematical model so that rubber sheeting should not be used for a serious mapping even it shows smaller discrepancies, but for the flat test area, an approximate 2D transformation can be accepted. Also although third-order polynomial is accurate in the proximity of GCPs and shows smaller discrepancies compared to the first- and the second-order polynomials, they can lead to significant errors for regions outside the GCP range and should not be used for a serious mapping. One can be considered the best resulted rectified image that obtained from second-order polynomial followed by the first-order polynomial. It was found in our study area that the minimum number of control points for each method gives accuracy better than a pixel. The first-order polynomial and rubber sheeting are good from the economical cost that they use minimum number of control points (three). It was found that the planimetric accuracy of rectified EgyptSat image met the 1:25,000 mapping standard (National Map Accuracy Standards). Also from the assessment of the information content of the EgyptSat image, it was found that it is consistent with the map scale of 1:25,000. In conclusion by analysis of the results, it is obvious that EgyptSat images are able to produce and update map of scale 1:25,000.

Smart Distribution: Coupled Microgrids

The distribution system provides major opportunities for smart grid concepts. One way to approach distribution system problems is to rethinking our distribution system to include the integration of high levels of distributed energy resources, using microgrid concepts. Basic objectives are improved reliability, promote high penetration of renewable sources, dynamic islanding, and improved generation efficiencies through the use of waste heat. Managing significant levels of distributed energy resources (DERs) with a wide and dynamic set of resources and control points can become overwhelming. The best way to manage such a system is to break the distribution system down into small clusters or microgrids, with distributed optimizing controls coordinating multimicrogrids. The Consortium for Electric Reliability Technology Solutions (CERTSs) concept views clustered generation and associated loads as a grid resource or a “microgrid.” The clustered sources and loads can operate in parallel to the grid or as an island. This grid resource can disconnect from the utility during events (i.e., faults, voltage collapses), but may also intentionally disconnect when the quality of power from the grid falls below certain standards. This paper focuses on DER-based distribution, the basics of microgrids, possibility of smart distribution systems using coupled microgrid and the current state of autonomous microgrid technology.

A Nonrigid Registration Framework Using Spatially Encoded Mutual Information and Free-Form Deformations

Mutual information (MI) registration including spatial information has been shown to perform better than the traditional MI measures for certain nonrigid registration tasks. In this work, we first provide new insight to problems of the MI-based registration and propose to use the spatially encoded mutual information (SEMI) to tackle these problems. To encode spatial information, we propose a hierarchical weighting scheme to differentiate the contribution of sample points to a set of entropy measures, which are associated to spatial variable values. By using free-form deformations (FFDs) as the transformation model, we can first define the spatial variable using the set of FFD control points, and then propose a local ascent optimization scheme for nonrigid SEMI registration. The proposed SEMI registration can improve the registration accuracy in the nonrigid cases where the traditional MI is challenged due to intensity distortion, contrast enhancement, or different imaging modalities. It also has a similar computation complexity to the registration using traditional MI measures, improving up to two orders of magnitude of computation time compared to the traditional schemes. We validate our algorithms using phantom brain MRI, simulated dynamic contrast enhanced mangetic resonance imaging (MRI) of the liver, and in vivo cardiac MRI. The results show that the SEMI registration significantly outperforms the traditional MI registration.

A method for monitoring shallow seagrass meadows ( Zostera spp.) using terrestrial oblique large-scale photography

Different monitoring methodologies are available to quantify the spatial distribution of seagrass beds, but repeated coverage over short time intervals is usually expensive or impossible. Sampling resolution is also a limiting factor, due to costs and manpower. We propose a low-cost alternative that allows for the free definition of sampling frequency and resolution. Since January 2006, a shallow seagrass meadow ( Zostera spp.) (Sado estuary, Portugal), has been monitored using true color large-scale oblique terrestrial photographs taken monthly during low-water spring tides, from a fixed elevated point. To rectify the images and create an orthogonal view, a set of ground control points (GCPs) were taken in and around the meadow, each coupled with a photograph. The photo-coordinates of each GCP were matched to its geographic coordinates, and a 2nd degree polynomial adjustment was used, to rectify every subsequent monthly photograph (RMS error of 0.7 m and final resolution of 0.5 m). An unsupervised classification was performed on the rectified images to map and quantify the meadow area. The meadow showed a seasonal cycle typical of temperate areas, in response to the annual cycle of solar radiation, with maximum coverage (∼1 ha) in late summer/early fall, and minimum areas (∼0.5 ha) in late winter/early spring. A marked shift in the meadow distribution was also found, with ∼25% average annual change (Index of relative change) and ∼43% change over the 4-year period studied. These results suggest that the method performed consistently, over time and over a range of varying environmental conditions, its main limitation being the need for an elevated point overlooking the area of interest. Whenever elevated viewpoints exist overlooking seagrass meadows or other intertidal or shallow subtidal coastal habitats, this methodology, may constitute a viable and economically advantageous alternative to other more costly approaches, e.g. aerial photography.

Partial shape-preserving splines

A complex geometric shape is often a composition of a set of simple ones, which may differ from each other in terms of their mathematical representations and the ways in which they are constructed. One of the necessary requirements in combining these simple shapes is that their original shapes can be preserved as much as possible. In this paper, a set of partial shape-preserving (PSP) spline basis functions is introduced to smoothly combine a collection of shape primitives with flexible blending range control. These spline basis functions can be considered as a kind of generalization of traditional B -spline basis functions, where the shape primitives used are control points or control polygons. The PSP-spline basis functions have all the advantages of the conventional B -spline technique in the sense that they are nonnegative, piecewise polynomial and of property of partition of unity. However, PSP-spline is a more powerful freeform geometric shape design technique in the sense that it is also a kind of shape-preserving spline. In addition, the PSP-spline technique implicitly integrates the weights of shape control primitives into its basis functions, which allows users to design a required geometric shape based on weighted control primitives. Though its basis functions are simply piecewise polynomial functions, it has the same shape design strengths as the rational piecewise polynomial based spline techniques such as NURBS. In particular, when control shape primitives are specified as a set of control points, PSP-spline behaves like a polygon smoother, with which a shape can be designed to approximate the specified control polygon or control mesh smoothly with any required precision. Consequently, a richer set of geometric shapes can be built using a relatively smaller set of control points.

Influences of forest roads on the spatial pattern of wildfire boundaries

Although many studies have examined fire ignition and fire spread, the cessation of fire is largely unexplored at a landscape scale. Therefore, we sought to examine the effects of forest roads on fire boundary locations. We analysed six fires within the Wenatchee National Forest in Washington State. Geographic Information System datasets of fire boundaries and environmental variables were obtained from government agencies. Case points were sampled on the fire boundaries, and five matching control points were sampled inside the fire boundary for each case. Matched case–control logistic regression was performed to identify the environmental differences between each case and its set of control points. We found that for four of the fires, fire boundaries were significantly closer to roads than to random control points. Various terrain and vegetation attributes were also correlated with fire boundary locations. In the fires where road effects were significant, they had stronger effects than any of the other environmental constraints on fire boundary locations. These results suggest that road effects on fire cessation should be incorporated more explicitly into landscape-level assessment of wildfire risk and analyses of fuel treatment effectiveness.