Ghost Points Research Articles

Real Multitouch Panel Without Ghost Points Based on Resistive Patterning

The real multitouch panel without ghost points is investigated using the structural patterns and an algorithm matrix of the two configurations. The pixels of patterns on the multitouch panel include virtual high and low resistances. The algorithm matrix with two configurations of equivalent circuit is derived using a voltage divider rule for array scanning. The fabrication process of structural patterns is carried out using microelectromechanical systems technology. The optical transmittance and absorbance of the multitouch panel in the UV, Vis, and IR regions are measured using a spectrophotometer. The multitouch panel, containing an array of 30 × 30, has a pixel size of 2 × 2 mm2 and a pitch distance of 2 mm. The average values of high and low impedances are 53.23 and 9.3 kΩ, respectively. The maximum transmittance is about 74.2% at the wavelength of 692 nm. The multitouch panel based on high and low impedance patterns has good adjacent touch resolution for reality multitouch applications. In addition, the patterned design and the algorithm matrix provide unlimited multitouch points and avoid the ghost points.

FAST RANGE IMAGE SEGMENTATION FOR A DOMESTIC SERVICE ROBOT

In this paper we present a fast approach to range image segmentation. The segmentation results are intended to serve as input to the perception system of a domestic service robot. In the first step “ghost points” at depth discontinuities are identified. This is followed by extracting step and roof edges. Planar patches are detected with a focus on horizontal and vertical planar structures. Finally, the range data is labelled with the locally dominant features, which results in a label map. Our approach was tested on real range images recorded in a home-like office environment using a tilting laser range finder.

A Fourth Order Accurate Finite Difference Scheme for the Elastic Wave Equation in Second Order Formulation

We present a fourth order accurate finite difference method for the elastic wave equation in second order formulation, where the fourth order accuracy holds in both space and time. The key ingredient of the method is a boundary modified fourth order accurate discretization of the second derivative with variable coefficient, (μ(x)u x ) x . This discretization satisfies a summation by parts identity that guarantees stability of the scheme. The boundary conditions are enforced through ghost points, thereby avoiding projections or penalty terms, which often are used with previous summation by parts operators. The temporal discretization is obtained by an explicit modified equation method. Numerical examples with free surface boundary conditions show that the scheme is stable for CFL-numbers up to 1.3, and demonstrate a significant improvement in efficiency over the second order accurate method. The new discretization of (μ(x)u x ) x has general applicability, and will enable stable fourth order accurate approximations of other partial differential equations as well as the elastic wave equation.

A new conservative method for the unsteady heat equation

A new conservative finite difference scheme for the unsteady heat equation is proposed. The new numerical scheme is a simplified version of mimetic methods, it satisfies a discrete version of Green’s theorem, and it does not use ghost points at any stage of its development. Its formulation will be presented in terms of a simple matricial form, which covers the full range of time evaluations. This feature allows us to present a complete and elegant convergence analysis. Its precision is quadratic at the boundary so an overall higher order convergence rate, compared with finite difference methods, is achieved in space. Numerical tests show the advantage of the new scheme when its linear systems are solved by iterative Krylov methods.

The Influence of Target Micromotion on SAR and GMTI

This paper analyzes the influence of typical target micromotions on synthetic aperture radar (SAR) images, azimuth resolution limit, SAR/ground moving target indication (GMTI), and MTI. According to the micromotion periods contained in the coherent processing interval, a new range model expansion and a generalized paired echo principle are proposed and applied to underlie the analysis. Several new kinds of image characteristics including gray strips, ghost points, and fences are reported, which are sheerly distinct from those of slow movers. Micromotion will also cause a prominent range cell migration even if its amplitude is far smaller than the range resolution. SAR/GMTI and MTI techniques will, in general, become invalid for micromotion targets. The influence is eventually demonstrated by the simulated data in the airborne single-channel geometry, and it can be used for SAR image interpretation as well as passive jamming.

Self-Adaptive Illumination Method for Optical Multi-Touch System

The uneven illumination distribution would affect the accuracy and stability of an optical multi-touch system. In this paper, different self-adaptive methods based on the type of interference source are integrated. When the ambient lighting changes, the luminance of the captured image will changes accordingly. This method tests the type of interference source by the speed and the region of ambient lighting change, and uses different function to update the background image rapidly. Experimental results show that with the help of the presented solutions, the ghost points are efficiently reduced and the system can adapt to the changes of ambient lighting in only 1 second.

A ghost fluid Lattice Boltzmann method for complex geometries

SUMMARYA ghost fluid Lattice Boltzmann method (GF‐LBM) is developed in this study to represent complex boundaries in Lattice Boltzmann simulations of fluid flows. Velocity and density values at the ghost points are extrapolated from the fluid interior and domain boundary via obtaining image points along the boundary normal inside the fluid domain. A general bilinear interpolation algorithm is used to obtain values at image points which are then extrapolated to ghost nodes thus satisfying hydrodynamic boundary conditions. The method ensures no‐penetration and no‐slip conditions at the boundaries. Equilibrium distribution functions at the ghost points are computed using the extrapolated values of the hydrodynamic variables, while non‐equilibrium distribution functions are extrapolated from the interior nodes. The method developed is general, and is capable of prescribing Dirichlet as well as Neumann boundary conditions for pressure and velocity. Consistency and second‐order accuracy of the method are established by running three test problems including cylindrical Couette flow, flow between eccentric rotating cylinders and flow over a cylinder in a confined channel. Copyright © 2011 John Wiley & Sons, Ltd.

A high order moving boundary treatment for compressible inviscid flows

We develop a high order numerical boundary condition for compressible inviscid flows involving complex moving geometries. It is based on finite difference methods on fixed Cartesian meshes which pose a challenge that the moving boundaries intersect the grid lines in an arbitrary fashion. Our method is an extension of the so-called inverse Lax–Wendroff procedure proposed in [17] for conservation laws in static geometries. This procedure helps us obtain normal spatial derivatives at inflow boundaries from Lagrangian time derivatives and tangential derivatives by repeated use of the Euler equations. Together with high order extrapolation at outflow boundaries, we can impose accurate values of ghost points near the boundaries by a Taylor expansion. To maintain high order accuracy in time, we need some special time matching technique at the two intermediate Runge–Kutta stages. Numerical examples in one and two dimensions show that our boundary treatment is high order accurate for problems with smooth solutions. Our method also performs well for problems involving interactions between shocks and moving rigid bodies.

Optical panel with full multitouch using patterned indium tin oxide

This study proposes an optical panel with full multitouch using the patterned indium tin oxide (ITO) and an algorithm matrix to avoid ghost points. The patterned ITOs include the virtual high and low impedances. The algorithm matrix with two configurations of equivalent circuits for array scanning is derived using the voltage divider rule. The fabrication process of the multitouch panel is carried out using microelectromechanical systems technology. The optical characteristics of the multitouch panel in the UV, visible, and IR regions are measured using photometric analysis. The multitouch panel, containing sensing pixels of 30×30 arrays, has a pixel size of 2×2 mm2 and a pitch distance of 2 mm. The average values of high and low impedances are 53.23 and 9.3 k Ω, respectively. The maximum transmittance is about 74.2% at the wavelength of 692 nm. The multitouch panel based on high and low impedance patterns has been specifically designed to offer good adjacent touch resolution and sensitivity for reality multitouch applications. In addition, the patterned design and the algorithm matrix provide unlimited multitouch points and avoid ghost points.

Ghost points in inverse scattering constructions of stationary Einstein metrics

We prove a removable singularities theorem for stationary Einstein equations, with useful implications for constructions of stationary solutions using soliton methods.

Adaptive mesh refinement based on high order finite difference WENO scheme for multi-scale simulations

In this paper, we propose a finite difference AMR-WENO method for hyperbolic conservation laws. The proposed method combines the adaptive mesh refinement (AMR) framework [4,5] with the high order finite difference weighted essentially non-oscillatory (WENO) method in space and the total variation diminishing (TVD) Runge–Kutta (RK) method in time (WENO-RK) [18,10] by a high order coupling. Our goal is to realize mesh adaptivity in the AMR framework, while maintaining very high (higher than second) order accuracy of the WENO-RK method in the finite difference setting. The high order coupling of AMR and WENO-RK is accomplished by high order prolongation in both space (WENO interpolation) and time (Hermite interpolation) from coarse to fine grid solutions, and at ghost points. The resulting AMR-WENO method is accurate, robust and efficient, due to the mesh adaptivity and very high order spatial and temporal accuracy. We have experimented with both the third and the fifth order AMR-WENO schemes. We demonstrate the accuracy of the proposed scheme using smooth test problems, and their quality and efficiency using several 1D and 2D nonlinear hyperbolic problems with very challenging initial conditions. The AMR solutions are observed to perform as well as, and in some cases even better than, the corresponding uniform fine grid solutions. We conclude that there is significant improvement of the fifth order AMR-WENO over the third order one, not only in accuracy for smooth problems, but also in its ability in resolving complicated solution structures, due to the very low numerical diffusion of high order schemes. In our work, we found that it is difficult to design a robust AMR-WENO scheme that is both conservative and high order (higher than second order), due to the mass inconsistency of coarse and fine grid solutions at the initial stage in a finite difference scheme. Resolving these issues as well as conducting comprehensive evaluation of computational efficiency constitute our future work.

The properties of terrestrial laser system intensity for measuring leaf geometries: a case study with Conference Pear trees (Pyrus communis).

Light Detection and Ranging (LiDAR) technology can be a valuable tool for describing and quantifying vegetation structure. However, because of their size, extraction of leaf geometries remains complicated. In this study, the intensity data produced by the Terrestrial Laser System (TLS) FARO LS880 is corrected for the distance effect and its relationship with the angle of incidence between the laser beam and the surface of the leaf of a Conference Pear tree (Pyrus Commmunis) is established. The results demonstrate that with only intensity, this relationship has a potential for determining the angle of incidence with the leaves surface with a precision of ±5° for an angle of incidence smaller than 60°, whereas it is more variable for an angle of incidence larger than 60°. It appears that TLS beam footprint, leaf curvatures and leaf wrinkles have an impact on the relationship between intensity and angle of incidence, though, this analysis shows that the intensity of scanned leaves has a potential to eliminate ghost points and to improve their meshing.

高功率激光装置中鬼光束的计算机分析

Using a self-made software named CatchGhost the ghost points’ position and energy in a coaxial optic systems were calculated accurately in a short time without omission．The software can carry out massive calculation in a short time, and pick out the harmful ghosts in system automatically. Because all the elements which are related to beams’energy, including the pinhole’ effect, reflectivity, gain and loss, are counted, data of ghost points given by the software are exact and useful．

A Cartesian grid method for two‐phase gel dynamics on an irregular domain

AbstractWe develop a numerical method for simulating models of two‐phase gel dynamics in an irregular domain using a regular Cartesian grid. The models consist of transport equations for the volume fractions of the two phases, polymer network and solvent; coupled momentum equations for the two phases; and a volume‐averaged incompressibility constraint. Multigrid with Vanka‐type box relaxation scheme is used as a preconditioner for the Krylov subspace solver (GMRES) to solve the momentum and incompressibility equations. Ghost points are used to enforce no‐slip boundary conditions for the velocity field of each phase, and no‐flux boundary conditions for the volume fractions. The behavior of the new method, including its rate of convergence, is explored through numerical experiments for a problem in which strong phase separation develops from an initially (almost) homogeneous phase distribution. We also use the method to explore situations, motivated by biology, which show that imposed boundary velocities can cause substantial redistribution of network and solvent. Copyright © 2010 John Wiley & Sons, Ltd.

Crack imaging by scanning pulsed laser spot thermography

A new crack imaging technique is presented that is based on second derivative image processing of thermal images of laser heated spots. Experimental results are shown that compare well with those obtained by the dye penetrant inspection method. A 3D simulation has been developed to simulate heat flow from a laser heated spot in the proximity of a crack. A ‘ghost point’ method has been used to deal efficiently with cracks having openings in the micometre range. Results are presented showing the effects of crack geometry and system parameters on thermal images of laser heated spots.

Inverse Lax-Wendroff procedure for numerical boundary conditions of conservation laws

We develop a high order finite difference numerical boundary condition for solving hyperbolic conservation laws on a Cartesian mesh. The challenge results from the wide stencil of the interior high order scheme and the fact that the boundary intersects the grids in an arbitrary fashion. Our method is based on an inverse Lax-Wendroff procedure for the inflow boundary conditions. We repeatedly use the partial differential equation to write the normal derivatives to the inflow boundary in terms of the time derivatives and the tangential derivatives. With these normal derivatives, we can then impose accurate values of ghost points near the boundary by a Taylor expansion. At outflow boundaries, we use Lagrange extrapolation or least squares extrapolation if the solution is smooth, or a weighted essentially non-oscillatory (WENO) type extrapolation if a shock is close to the boundary. Extensive numerical examples are provided to illustrate that our method is high order accurate and has good performance when applied to one and two-dimensional scalar or system cases with the physical boundary not aligned with the grids and with various boundary conditions including the solid wall boundary condition. Additional numerical cost due to our boundary treatment is discussed in some of the examples.

Improving SVM classification on imbalanced time series data sets with ghost points

Imbalanced data sets present a particular challenge to the data mining community. Often, it is the rare event that is of interest and the cost of misclassifying the rare event is higher than misclassifying the usual event. When the data is highly skewed toward the usual, it can be very difficult for a learning system to accurately detect the rare event. There have been many approaches in recent years for handling imbalanced data sets, from under-sampling the majority class to adding synthetic points to the minority class in feature space. However, distances between time series are known to be non-Euclidean and non-metric, since comparing time series requires warping in time. This fact makes it impossible to apply standard methods like SMOTE to insert synthetic data points in feature spaces. We present an innovative approach that augments the minority class by adding synthetic points in distance spaces. We then use Support Vector Machines for classification. Our experimental results on standard time series show that our synthetic points significantly improve the classification rate of the rare events, and in most cases also improves the overall accuracy of SVMs. We also show how adding our synthetic points can aid in the visualization of time series data sets.

A new accurate finite difference scheme for Neumann (insulated) boundary condition of heat conduction

The Neumann (or insulated) boundary condition is often encountered in engineering applications. The conventional finite difference schemes are either first-order accurate or second-order accurate but need a ghost point outside the boundary. Compact finite difference schemes are difficult to apply for multi-dimensional cases or for cylindrical and spherical coordinate cases. In this study, we present a kind of new and accurate finite difference schemes for the Neumann (insulated) boundary condition in Cartesian, cylindrical, and spherical coordinates, respectively. Combined with the Crank–Nicholson finite difference method or other higher-order methods, the overall scheme is proved to be unconditionally stable and provides much more accurate numerical solutions. The numerical errors and convergence rates of the solution are tested by several examples. Results show that the new method is promising.

Efficient borehole detection from single scan data

This work presents a fast and robust method to precisely segment and locate boreholes of 4–50 mm diameter. The task is solved by scanning over the expected borehole location given by CAD data. Since the diameter of the borehole is known, this can be used to obtain a robust and fast algorithm suitable for industrial application. Single scan data is sufficient to segment the bore independent of bore chamfer type using a robust normal vector fit and a classification based on the Gaussian image. A sequential cylinder fit algorithm makes it possible to calculate the bore pose in less than one second. The experiments demonstrate that 120° of the borehole surface are sufficient for robust localization within 0.3 mm and 0.5° even in the presence of ghost points and notches in the boreholes.

Natural neighbor extrapolation using ghost points

Among locally supported scattered data schemes, natural neighbor interpolation has some unique features that makes it interesting for a range of applications. However, its restriction to the convex hull of the data sites is a limitation that has not yet been satisfyingly overcome. We use this setting to discuss some aspects of scattered data extrapolation in general, compare existing methods, and propose a framework for the extrapolation of natural neighbor interpolants on the basis of dynamic ghost points.