缩小采样区域的蒙特卡罗移动节点定位算法

针对无线传感器网络中移动节点定位问题,提出一种适用于未知节点移动而信标节点固定的改进蒙特卡罗定位算法,充分利用信标节点与未知节点间的测距误差来缩小采样区域,提高采样效率。仿真结果表明,改进算法在信标节点密度、连通度和节点最大运动速度等不同情况下均能提高定位精度,减少采样次数和计算量,延长网络的生存周期。     

Sketch guided solid texturing

Compared to 2D textures, solid textures can represent not only the bounding surfaces, but also their interiors. Existing solid texture synthesis methods pay little attention to the generation of conforming textures that capture geometric structures or reflect the artists’ design intentions. In this paper, we propose a novel approach to synthesizing solid textures using 2D exemplars. The generated textures locally agree with a tensor field derived from user sketching curves. We use a deterministic approach and only a small portion of the voxels needs to be synthesized on demand. Correction is fundamental in deterministic texture synthesis. We propose a history windows representation, which is general enough to unifiedly represent various previous correction schemes, and a dual grid scheme based on it to significantly reduce the dependent voxels while still producing high quality results. Experiments demonstrate that our method produces significantly improved solid textures with a small amount of user interaction.     

Geometric texturing using level sets

We present techniques for warping and blending (or subtracting) geometric textures onto surfaces represented by high resolution level sets. The geometric texture itself can be represented either explicitly as a polygonal mesh or implicitly as a level set. Unlike previous approaches, we can produce topologically connected surfaces with smooth blending and low distortion. Specifically, we offer two different solutions to the problem of adding fine-scale geometric detail to surfaces. Both solutions assume a level set representation of the base surface which is easily achieved by means of a mesh-to-level-set scan conversion. To facilitate our mapping, we parameterize the embedding space of the base level set surface using fast particle advection. We can then warp explicit texture meshes onto this surface at nearly interactive speeds or blend level set representations of the texture to produce high-quality surfaces with smooth transitions.     

Constructive texturing based on hypervolume modeling

The concept of solid texturing is extended in two directions: constructive modeling of space partitions for texturing and modeling of multidimensional textured objects called hypervolumes. A hypervolume is considered as a point set with attributes of both physical (density, temperature, etc.) and photometric (color, transparency, diffuse and specular reflections, etc.) nature. The point set geometry and attributes are modeled independently using real‐valued scalar functions of several variables. Each real‐valued function defining geometry or an attribute is evaluated at the given point by a procedure traversing a constructive tree structure with primitives in the leaves and operations in the nodes of the tree. This approach provides a framework for modeling, texturing and visualization of 3D solids, time‐dependent and multidimensional objects in a completely uniform manner. We introduced a special modeling language and implemented software tools supporting the proposed approach. The concept of constructive hypervolume textures is independent of the geometry representation. We provide examples of textured Frep and BRep objects as illustrations. Copyright © 2002 John Wiley & Sons, Ltd.     

Texram: a smart memory for texturing

Logic embedded memory is an emerging technology that combines high transfer rates and computing power. Texram implements this technology and a new filtering algorithm to achieve high speed, high quality texture mapping. Integrating arithmetic units and large memory arrays on the same chip and thus exploiting the enormous internal transfer rates provides an elegant solution to the memory access bottleneck of high quality texture mapping. Using this technology, we can not only achieve higher texturing speed at lower system costs, we can also incorporate new functionalities such as detail mapping and footprint assembly to produce higher quality images at real time rendering speeds. Environment and video mapping are also integrated on the Texram, which therefore represents an autonomous and versatile texturing coprocessor. Logic enhanced memories might become the computing paradigm of the future, not just in graphics applications. Technological advances will foster this trend by providing an ever increasing amount of memory capacity and chip space for arithmetic units. As the ultimate solution, we can expect a complete 3D graphics pipeline including all memory systems integrated on a single chip     

Zeros of sampled systems

The zeros of the discrete-time system obtained when sampling a continuous time system are explored. Theorems for the limiting zeros for large and small sampling periods are given. Conditions which guarantee that the sampled system has stable zeros are also presented.     

Multiple kernels noise for improved procedural texturing

Procedural texturing is a well known method to synthesize details onto virtual surfaces directly during rendering. But the creation of such textures is often a long and painstaking task. This paper introduces a new noise function, called multiple kernels noise. It is characterized by an arbitrary energy distribution in spectral domain. Multiple kernels noise is obtained by adaptively decomposing a user-defined power spectral density (PSD) into rectangular regions. These are then associated to kernel functions used to compute noise values by sparse convolution. We show how multiple kernels noise (1)?increases the variety of noisy procedural textures that can be modeled and (2)?helps creating structured procedural textures by automatic extraction of noise characteristics from user-supplied samples.     

Classifying non-uniformly sampled vector-valued curves

We propose a novel means of classifying vector-valued curves using functional principal components. This uses cross-validation to select curve components, the degree of smoothing and scores associated with the best classification performance. Our approach is well suited to data generated by sensors of different modalities and time varying sampling frequencies. Experimental comparisons show this approach has significant advantages over conventional techniques using non-uniformly sampled data. Our approach also generates novel forms of derivative analysis, a widely used technique for classifying spectral functions from contaminated data.     

Field modeling with sampled distances

Traditional mesh-based approaches to the modeling and analysis of physical fields within geometric models require some form of topological reconstruction and conversion in the mesh generation process. Such manipulations tend to be tedious and error-prone manual processes that are not easily automated. We show that most field problems may be solved directly by using approximate distance fields computed from designed or sampled geometric data, thus avoiding many of the difficult reconstruction and meshing problems. With distances we can model fields that satisfy boundary conditions while approximating the governing differential equations to arbitrary precision. Because the method is based on sampling, it provides natural control for multi-resolution both in geometric detail of the domain and in accuracy of the computed physical field. We demonstrate the field modeling capability with several heat transfer applications, including a typical transient problem and a ‘scan and solve’ approach to the simulation of a physical field in a real-world artifact.     

Adaptive stabilization of sampled systems

A simple discrete adaptive control scheme is proposed for stabilizing minimum phase continuous time systems under fast sampling. Even though the sampled system is not necessarily minimum phase, information about the pole-zero locations of the sampled system can be incorporated to complete the proof of stability.     

RotoTexture: automated tools for texturing raw video

We propose a video editing system that allows a user to apply a time-coherent texture to a surface depicted in the raw video from a single uncalibrated camera, including the surface texture mapping of a texture image and the surface texture synthesis from a texture swatch. Our system avoids the construction of a 3D shape model and instead uses the recovered normal field to deform the texture so that it plausibly adheres to the undulations of the depicted surface. The texture mapping method uses the nonlinear least-squares optimization of a spring model to control the behavior of the texture image as it is deformed to match the evolving normal field through the video. The texture synthesis method uses a coarse optical flow to advect clusters of pixels corresponding to patches of similarly oriented surface points. These clusters are organized into a minimum advection tree to account for the dynamic visibility of clusters. We take a rather crude approach to normal recovering and optical flow estimation, yet the results are robust and plausible for nearly diffuse surfaces such as faces and t-shirts     

Control of the quality of laser surface texturing

Since the conception of the first lasers in the 60’s, the knowledge and consequently the applications of laser have been widely increased. Laser surface texturing is a specific field among the various applications of the laser. This technique is employed in the aim of improving tribological performances for instance. This paper presents the laser surface texturing of a heterogeneous material. This material is lamellar cast iron. It has been chosen for its good friction properties. The textured surface is composed of grooves or dimples. The dimensions are micrometric. For the grooves, different cross sections have been engraved: semicircular, rectangular, trapezoidal and triangular. The dimples are cylindrical. All these laser textured surfaces are engraved with the laser manufacturing machine: DML 40 SI of Gildemeister (Germany). This machine is equipped with a galvanometric scanner, which allows tilted surfaces to be engraved. Various machining strategies and the following results are discussed in function of the different desired laser surface texturing results. In addition, to increase the aspect of the engraved surfaces, laser polishing is employed. Thanks to a defocalisation of the laser beam on the surface, the material is not ablated but melted. To be able to compare the different laser machining process, several techniques of control have been used: roughness profilometry, scanning electron microscopy and non contacting optical measurement. The rules of use of these methods must be defined bearing in mind their inherent limitations.     

Limit results for sampled systems

Properties of discrete time systems obtained by sampling continuous time systems are described. By introducing prefilters, we can treat different ways of sampling within one framework. Results on the convergence of poles and zeros of transfer functions and noise filters as the sampling interval tends to zero are given. These results are generalizations of the results of Åström, Hagander and Sternby (1984) on the convergence of poles and zeros for zero-order hold sampled transfer functions. Sampled noise models are also analysed. Knowledge of these properties is very important in, for example, discrete time simulations of continuous time systems, and identification of continuous time models based on discrete time measurements.     

Deadbeat sampled system direct synthesis

A direct synthesis method is presented for obtaining a discrete compensator to produce a finite-settling-time transient in response to a prescribed input with no intersample transient terms after the finite settling time. The method is applicable to a single constant-frequency sampler in a feedback system with any type of hold for any polynomial input. The method uses a fictitious sampler at the output with sample timeT/mto scan the intersample times and to obtain criteria for deadbeat transients. The criteria are derived from root locus considerations but are applied to Laplace transforms containing both functions ofsand functions ofzso that the only operations are analytic ones.     

Parametric interpolation using sampled data

Trajectory in high-speed precision machining requires very small feed-rate fluctuation and contour error, which can be achieved with parametric interpolation. Since it is impossible to exactly compute the arc-length of a general parametric curve, the conventional parametric interpolation obtains a parameter through a real-time update. Thus it cannot be used with a preplanned feed-rate profile, which restricts its applications. To overcome such a problem, the proposed algorithm estimate parameters using tabulated parameter and length data. The simulations show the proposed method useful with smaller contour error and acceptable feed-rate fluctuation comparable to the second order real-time parametric interpolation.     

Optimization of non-uniformly sampled discrete systems

This paper deals with a general method for the optimization of multivariable systems with non-uniform sampling chosen in an optimal way. The algorithm is based on Dynamic Programming and is applied to extend the Kalman-Koepcke optimization method for a linear dynamic system, with a quadratic performance index. In the general multivariable case, the method implies the solution of a two-point boundary value problem. In the scalar case, which has only one input and one output, the sampling periods may be found separately from the control law. The computational difficulties connected with the implementation of the method are discussed and simplifications, possible for discretized continuous systems, are derived. Numerical examples are given.     

Transforming differential domains into sampled representations

The need often arises in dealing with sampled control mechanisms to transform physical system models intoZ- domain representations. The technique discussed applies a dated, but powerful, matrix technique to form an effective algorithm for performing this transformation by computer.     

面泊松融合结合色彩变换的无缝纹理辐射处理

目的：消除三维模型纹理接缝上的辐射差异,实现接缝处色彩的自然、连续的过渡。方法：本文在标准的泊松融合（Poisson Blending）基础上,结合色彩变换技术（Color Transfer）,提出了一种新的以面为基元的泊松融合无缝纹理辐射处理方法。首先以影像上的纹理三角形为处理单元,以色彩变换参数为未知数,根据模型的三角网边邻接拓扑关系建立泊松方程组,然后全局最小二乘解求局部色彩变换参数,最后进行全局最优解下的局部色彩变换。结果：既保证了色彩的均匀过渡,又能更好的改正影像间的整体色差。结论：相比使用标准的像素级泊松融合方法进行无缝纹理处理,本文的方法拥有计算上的优势,更适合于复杂模型的处理,且有更好的整体色差改正与过渡效果。理论分析和大量试验证明了本文方法的优越性。     

Numerical integration of sparsely sampled data

In experimental work as well as in computational applications for which limited computational resources are available for the numerical calculations a coarse mesh problem frequently appears. In particular, we consider here the problem of numerical integration when the integrand is available only at nodes of a coarse uniform computational grid. Our research is motivated by the coarse mesh problem arising in ecological applications such as pest insect monitoring and control. In our study we formulate a criterion for assessing mesh coarseness and demonstrate that the definition of a coarse mesh depends on the integrand function. We then discuss the accuracy of computations on coarse meshes to conclude that the conventional methods used to improve accuracy on fine meshes cannot be applied to coarse meshes. Our discussion is illustrated by numerical examples.