Computing global visibility maps for regions on the boundaries of polyhedra using Minkowski sums

A global visibility map is a spherical image built to describe the complete set of global visible view directions for a surface. In this paper, we consider the computation of global visibility maps for regions on the boundary of a polyhedron. Both the self-occlusions introduced by a region and the global occlusions introduced by the rest of the surfaces on the boundary of the polyhedron are considered for computing a global visibility map. We show that the occluded view directions introduced between a pair of polyhedral surfaces can be computed from the spherical projection of the Minkowski sum of one surface and the reflection of the other. A suitable subset of the Minkowski sum, which shares the identical spherical projection with the complete Minkowski sum, is constructed to obtain the spherical images representing global occlusions. Our method has been successfully tested on many CAD models. It extends the previous methods for computing global visibility maps using convex decomposition, and it exhibits a better performance.     

改进的实时反走样透视阴影图算法及实现

为解决透视阴影图算法中,物体被非线性比例导致愈加明显的自阴影或表面波纹现象,提出一种基于GPU的实时反走样透视阴影图改进算法。该算法结合透视阴影图算法以及D.Weiskopf的dual depth layers算法,通过采用GPU深度剥离技术采样场景的双层深度值信息,并引入自适应偏移量zbias来计算场景的深度偏移量。该算法采用C语言实现,同时使用GPU顶点渲染器和像素渲染器编程有效避免程序复杂度。实验结果表明,该改进算法较好解决了透视阴影图的自阴影问题,提高了渲染阴影质量。     

不同类型高度图控制浅浮雕模型生成方法

目的 数字浅浮雕是在平面载体上塑造高低起伏形象的一种造型艺术,具有独特的结构及视觉效果,应用场景极为广泛。为了增加数字浮雕设计的多样性,实现浮雕的风格化应用,提出一种基于高度图的浅浮雕模型生成方法。方法 引入掩模理论,利用掩模操作对待处理的图像进行处理,融合图像处理技术,控制所要生成浮雕不同部位的高度,得到控制浮雕生成效果的高度图,借鉴已有的浅浮雕模型生成方法,利用基于高斯混合模型的滚动引导法向滤波（Gaussian mixture model based rolling guidance normal filtering,GRNF）进行法向分解,基于SfG （surface from gradients）的局部调整和全局重建的方法进行曲面重建,采用拉普拉斯算子及双边滤波器进行去噪平滑处理,最终生成不同高度风格的浅浮雕模型。结果 实验结果表明,本文方法能够生成带有不同视觉效果的浅浮雕模型,通过对细节特征及结构特征相关参数的调整,均能够生成轮廓清晰、细节丰富的浅浮雕模型。结论 本文提出的基于高度图的浅浮雕模型生成方法能够为浅浮雕的多样化设计提供新的思路和方法,在家居装饰行业中有重要的应用价值。     

Efficient search of combinatorial maps using signatures

In this paper, we address the problem of computing canonical representations of n-dimensional combinatorial maps and of using them for efficiently searching for a map in a database. We define two combinatorial map signatures: the first one has a quadratic space complexity and may be used to decide an isomorphism with a new map in linear time whereas the second one has a linear space complexity and may be used to decide an isomorphism in quadratic time. We show that these signatures can be used to efficiently search for a map in a database.     

Constructing hexahedral shell meshes via volumetric polycube maps

Shells are three-dimensional structures. One dimension, the thickness, is much smaller than the other two dimensions. Shell structures can be widely found in many real-world objects. This paper presents a method to construct a layered hexahedral mesh for shell objects. Given a closed 2-manifold and the user-specified thickness, we construct the shell space using the distance field and then parameterize the shell space to a polycube domain. The volume parameterization induces the hexahedral tessellation in the object shell space. As a result, the constructed mesh is an all-hexahedral mesh in which most of the vertices are regular, i.e., the valence is 6 for interior vertices and 5 for boundary vertices. The mesh also has a layered structure, so that all layers have exactly the same tessellation. We prove that our parameterization is guaranteed to be bijective. As a result, the constructed hexahedral mesh is free of degeneracy, such as self-intersection, flip-over, etc. We also show that the iso-parametric line (in the thickness dimension) is orthogonal to the other two iso-parametric lines. We apply our algorithm to numerous real-world models of various geometry and topology. The promising experimental results demonstrate the efficacy of our algorithm. Although our main focus is to construct a hexahedral mesh by using volumetric polycube parameterization, the proposed framework is general that can be applied to other regular domains, such as cylinder and sphere, which is also demonstrated in the paper.     

On weakly cut-stable maps

A mapping f:P→Q between posets P and Q is called weakly cut-stable if f can be naturally extended to a weakly complete lattice homomorphism (i.e., preserving non-empty meets and joins) f^∗:N(P)→N(Q) between the corresponding Dedekind-MacNeille completions. These mappings are studied and described by the 1st-order language.     

视野驱动的自适应阴影图

阴影图是当前实时阴影绘制中的一种经典算法。该算法基于图像空间,当有限分辨率的阴影图映射到较大场景中时,就会由于采样不足造成锯齿形变走样。提出了一种实时的反走样阴影图算法,该算法首先获取当前视点所能够看到的场景范围,然后绘制该范围内的阴影图,并映射到场景中生成实时阴影。该方法同经典的阴影图算法相比,避免了场景中不必要的阴影绘制,提高了阴影图的利用率,反走样的效果很好。而且,该方法只需要绘制一到两幅阴影图,算法的实时性很强,可以满足一个上百万面片的大规模场景中实时阴影绘制的需要。     

双混沌映射的图像加密技术

为了提高图像加密算法的安全性和高效性,提出了一种分段Logistic混沌映射与Cat映射相结合的双混沌系统。首先由改进后的Logistic映射确定选用哪种映射进行迭代,从而确定混沌密钥,最后对算法的安全性进行分析。实验结果表明,该算法的密钥空间较大,并具有较高的初值敏感性和抗攻击能力,是一种新的有效的图像加密算法。     

SLAM问题中的模糊几何地图与顶点自定位法

在模糊几何地图的基础上提出了顶点定位法来解决机器人的室内SLAM中的实时自定位问题．顶点定位法是从传感信息中抽取多边形顶点作为路标进行定位．顶点定位法与传统的边匹配定位法比较有计算量小,定位精度高等优点．此外本文提出了基于空间距离的传感数据两次分类方法构建模糊几何地图,提高了数字地图精确度．实验结果表明其性能优于传统的方法．     

Effects of sense of direction on Internet skill and cognitive maps of the Web

The relationship of sense of direction in the real world to Internet use, as well as to cognitive maps of the Internet, was investigated. In Study 1, 28 participants were asked to draw a sketch map of the Internet. They also completed a questionnaire containing scales for measuring Internet usage, knowledge, and skill, and completed the Sense of Direction Questionnaire (SDQ-S), which is composed of two scales, awareness of orientation and memory for usual spatial behavior. In Study 2, 48 participants performed a modified sketch map task and completed the same questionnaires. Awareness of orientation improved the Internet skills of novices but not of experts. In addition, awareness of orientation affected the structure of the cognitive maps of the Internet. These results suggest that sense of direction in the real world influence skill with the Web for novice users.     

基于双混沌映射的文本hash函数构造*

提出了一种基于混沌Logistic 映射和斜帐篷映射的文本hash函数算法。该算法将明文信息分组并转换为相应的ASCII码值,然后把该值作为Logistic映射的迭代次数,迭代生成的值作为斜帐篷映射的初始值进行迭代,然后依据一定的规则从生成值中提取长度为128 bit的hash值。通过仿真对该算法的单向性、混乱与扩散、碰撞等性能进行分析,理论分析和仿真实验证明该算法可以满足hash函数的各项性能要求。     

Predicting helix pair structure from fuzzy contact maps

One approach to protein structure prediction is to first predict from sequence, a thresholded and binary 2D representation of a protein's topology known as a contact map. The predicted contact map can be used as distance constraints to construct a 3D structure. We focus on the latter half of the process for helix pairs and present an approach that aims to obtain a set of non-binary distance constraints from contacts maps. We extend the definition of “in contact” by incorporating fuzzy logic to construct fuzzy contact maps. Then, template-based retrieval and distance geometry bound smoothing were applied to obtain distance constraints in the form of a distance map. From the distance map, we can calculate the helix pair structure. Our experimental results indicate that distance constraints close to the true distance map could be predicted at various noise levels and the resulting structure was highly correlated to the predicted distance map.     

Perceived density of road maps

Maps should be designed so that users can comprehend and use the information. Display decisions, such as choosing the scale at which an area is shown, depend on properties of the displayed information such as the perceived density (PD) of the information. Taking a psychophysical approach we suggest that the PD of information in a road map is related to the scale and properties of the mapped area. 54 participants rated the PD of 60 maps from different regions. We provide a simple model that predicts the PD of electronic road map displays, using the logarithm of the number of roads, the logarithm of the number of junctions and the length of the shown roads. The PD model was cross-validated using a different set of 60 maps (n = 44). The model can be used for automatically adjusting display scales and for evaluating map designs, considering the required PD to perform a map-related task.     

Design and implementation of coupled chaotic maps in watermarking

The present paper proposes a multidimensional coupled chaotic map as a pseudo random number generator. Based on an introduced dynamical systems, a watermark scheme is presented. By modifying the original image and embedding a watermark in the difference values within the original image, the proposed scheme overcomes the problem of embedding a watermark in the spatial domain. As the watermark extraction does not require the original image, the introduced model can be employed for practical applications. This algorithm tries to improve the problem of failure of embedding in small key space, embedding speed and level of security.     

Monitoring industrial processes with SOM-based dissimilarity maps

Today’s large scale availability of data from industrial plants is an invaluable resource to monitor industrial processes. Data-based methods can lead to better understanding, optimization or detection of anomalies. As a particular case, batch processes have attracted special interest due to their widespread presence in the industry. The aim of monitoring, in this case, is to compare different runs or implementations of a process with the baseline or normal operating one. On the other hand, visual exploration tools for process monitoring have been a prolific application field for self-organizing maps (SOM). In this paper, we exploit data-based models, obtained by means of SOM, for the visual comparison of industrial processes. For that purpose, we propose a method that defines a new visual exploration tool, called dissimilarity map. We also expose the need to consider dynamic information for effective comparison. The method is assessed in two industrial pilot plants that implement the same process. The results are discussed.     

Trimming local and global self-intersections in offset curves/surfaces using distance maps

A robust and efficient algorithm for trimming both local and global self-intersections in offset curves and surfaces is presented. Our scheme is based on the derivation of a rational distance map between the original curve or surface and its offset. By solving a bivariate polynomial equation for an offset curve or a system of three polynomial equations for an offset surface, all local and global self-intersection regions in offset curves or surfaces can be detected. The zero-set of polynomial equation(s) corresponds to the self-intersection regions. These regions are trimmed by projecting the zero-set into an appropriate parameter space. The projection operation simplifies the analysis of the zero-set, which makes the proposed algorithm numerically stable and efficient. Furthermore, in a post-processing step, a numerical marching method is employed, which provides a highly precise scheme for self-intersection elimination in both offset curves and surfaces. The effectiveness of our approach is demonstrated using several experimental results.     

Co-adaptation of self-organizing maps by evolution and learning

This paper proposes two co-adaptation schemes of self-organizing maps that incorporate the Kohonen's learning into the GA evolution in an attempt to find an optimal vector quantization codebook of images. The Kohonen's learning rule used for vector quantization of images is sensitive to the choice of its initial parameters and the resultant codebook does not guarantee a minimum distortion. To tackle these problems, we co-adapt the codebooks by evolution and learning in a way that the evolution performs the global search and makes inter-codebook adjustments by altering the codebook structures while the learning performs the local search and makes intra-codebook adjustments by making each codebook's distortion small. Two kinds of co-adaptation schemes such as Lamarckian and Baldwin co-adaptation are considered in our work. Simulation results show that the evolution guided by a local learning provides the fast convergence, the co-adapted codebook produces better reconstruction image quality than the non-learned equivalent, and Lamarckian co-adaptation turns out more appropriate for the VQ problem.     

用于矢量数字地图的可逆数据隐藏算法

提出一种基于差值直方图的可逆数据隐藏算法,用于矢量地图的认证和隐秘通信。通过修改相邻顶点坐标的差值来实现数据隐藏。为减少由扩展嵌入所引起的图形失真,借助差值直方图来选取可嵌入差值,优先选择绝对值小的差值。与现有算法相比,本算法具有较高的嵌入率、较好的图形质量以及精确控制嵌入容量的能力。     

The three-state test for chaos detection in discrete maps

The three-state test (3ST) – a new approach for chaos detection in discrete chaotic maps is presented. The scheme is based on statistical analyses of patterns obtained from ascending sorting of the system states. In addition to its ability for clear discernment between chaotic, quasi-periodic and periodic dynamical systems, the detection of periods of stable cycles is also automated with 3ST. The method is directly applied on data series generated by chaotic maps and does not require a priori knowledge of the equations of the underlying system. It also presents the advantage of not having to depend on the nature of the vector field as well as its dimensionality and is computationally low cost. The effectiveness of the 3ST is confirmed using two well known and widely studied chaotic maps: the logistic map and the Henon 2D map.