Comparison of two image-space subdivision algorithms for direct volume rendering on distributed-memory multicomputers

Direct Volume Rendering (DVR) is a powerful technique for visualizing volumetric data sets. However, it involves intensive computations. In addition, most of the volumetric data sets consist of large number of 3D sampling points. Therefore, visualization of such data sets also requires large computer memory space. Hence, DVR is a good candidate for parallelization on distributed-memory multicomputers. In this work, image-space parallelization of Raycasting based DVR for unstructured grids on distributed-memory multicomputers is presented and discussed. In order to visualize unstructured volumetric datasets where grid points of the dataset are irregularly distributed over the 3D space, the underlying algorithms should resolve the point location and view sort problems of the 3D grid points. In this paper, these problems are solved using a Scanline Z-buffer based algorithm. Two image space subdivision heuristics, namely horizontal and recursive rectangular subdivision heuristics, are utilized to distribute the computations evenly among the processors in the rendering phase. The horizontal subdivision algorithm divides the image space into horizontal bands composed of consecutive scanlines. In the recursive subdivision algorithm, the image space is divided into rectangular subregions recursively. The experimental performance evaluation of the horizontal and recursive subdivision algorithms on an IBM SP2 system are presented and discussed. © Springer-Verlag Berlin Heidelberg 1996

Self-stabilizing Overlays for high-dimensional Monotonic Searchability

We extend the concept of monotonic searchability for self-stabilizing systems from one to multiple dimensions. A system is self-stabilizing if it can recover to a legitimate state from any initial illegal state. These kind of systems are most often used in distributed applications. Monotonic searchability provides guarantees when searching for nodes while the recovery process is going on. More precisely, if a search request started at some node $u$ succeeds in reaching its destination $v$, then all future search requests from $u$ to $v$ succeed as well. Although there already exists a self-stabilizing protocol for a two-dimensional topology and an universal approach for monotonic searchability, it is not clear how both of these concepts fit together effectively. The latter concept even comes with some restrictive assumptions on messages, which is not the case for our protocol. We propose a simple novel protocol for a self-stabilizing two-dimensional quadtree that satisfies monotonic searchability. Our protocol can easily be extended to higher dimensions and offers routing in $\mathcal O(\log n)$ hops for any search request

Аналого-цифровое кодирование рельефно-фазовых голограмм с использованием анизотропных сред

The basis of the modern methods of protecting products, goods, documents, and equities are holographic security technologies, the development of which indicates that they are improving, new equipment and materials appear, new methods of hologram recording are being developed, their manufacturability is increasing, identification and authentication are being simplified. Combined images are widely used in modern holography. When creating combined images, various optical effects arise, such as moire, parallax, color change, etc., which, in combination with each other, as well as with other images (microtext, hidden images, sequential numbering, marking, coding, chemical indicators), permit to use them both to protect documents and to obtain an original artistic effect. This article discusses combined protective elements based on a relief-phase hologram with a deposited polymer carrier layer containing a latent image visible in polarized light. This protective element is named crystallogram. In the process of developing a crystallogram, the synthesis of monomers and the preparation of an anisotropic polarizable composition was mastered, a layer of polymerizable liquid crystals (PLC) was obtained with a contrast visualization of a latent image. A technology was developed for combining the relief-phase hologram with the deposited polymer carrier layer with the subsequent blocking of the polarizable liquid crystals (PLC) layer by protective varnish layers.Основой современных методов защиты продукции, товаров, документов и ценных бумаг являются голографические защитные технологии, развитие которых свидетельствует о том, что они совершенствуются, появляются новые оборудование и материалы, разрабатываются новые методы записи голограмм, повышается их технологичность, упрощается идентификация и проверка подлинности. В современной голографии комбинированные изображения применяются очень широко. При создании комбинированных изображений возникают различные оптические эффекты, такие как муар, параллакс, изменение цвета и другие, которые в комбинации между собой, а также с другими изображениями (микротекст, скрытые изображения, последовательная нумерация, маркировка, кодирование, химические индикаторы) позволяют использовать их как для защиты документов, так и для получения оригинального художественного эффекта. В статье рассматриваются комбинированные защитные элементы на основе рельефно-фазовой голограммы с нанесенным полимерным слоем-носителем, содержащим скрытое изображение, видимое в поляризованном свете. Данный защитный элемент получил название «кристаллограмма». В процессе разработки кристаллограммы был освоен синтез мономеров и приготовление анизотропной поляризуемой композиции, получен слой полимеризуемых жидких кристаллов (ПЖК) с контрастной визуализацией скрытого изображения. Отработана технология совмещения рельефно-фазовой голограммы с нанесенным полимерным слоем-носителем с последующим блокированием слоя ПЖК защитными лаковыми слоями

Incremental rank updates for moving query points

Geographic Information Science International Conference (GIScience

DOI 10.1007/s00778-005-0001-y REGULAR PAPER

Abstract Peer-to-peer (P2P) networks have become a powerful means for online data exchange. Currently, users are primarily utilizing these networks to perform exact-match queries and retrieve complete files. However, future more data intensive applications, such as P2P auction networks, P2P job-search networks, P2P multiplayer games, will require the capability to respond to more complex queries such as range queries involving numerous data types including those that have a spatial component. In this paper, a distributed quadtree index that adapts the MX-CIF quadtree is described that enables more powerful accesses to data in P2P networks. This index has been implemented for various prototype P2P applications and results of experiments are presented. Our index is easy to use, scalable, and exhibits good load-balancing properties. Similar indices can be constructed for various multidimensional data types with both spatial and non-spatial components

Broadening Access to Large Online Databases by Generalizing Query Previews

Companies, government agencies, and other types of organizations are making their large databases available to the world over the Internet. Current database front-ends do not give users information about the distribution of data. This leads many users to waste time and network resources posing queries that have either zero-hit or mega-hit result sets. Query previews form a novel visual approach for browsing large databases. Query previews supply data distribution information about the database that is being searched and give continuous feedback about the size of the result set for the query as it is being formed. On the other hand, query previews use only a few pre-selected attributes of the database. The distribution information is displayed only on these attributes. Unfortunately, many databases are formed of numerous relations and attributes. This paper introduces a generalization of query previews. We allow users to browse all of the relations and attributes of a database using a hierarchical browser. Any of the attributes can be used to display the distribution information, making query previews applicable to many public online databases. (Also cross-referenced as UMIACS-TR-2000-32) (Also cross-referenced as HCIL-TR-2000-14

Opportunistic Sampling in Wireless Sensor Networks

ACM International Conference on Advances in Geographic Information Systems (SIGSPATIAL)In an active WSN where user queries are regularly processed, a significant proportion of nodes relay and overhear data generated by other nodes in the network. In this paper, we propose to exploit this mode of data communication towards a gradual buildup of global knowledge. We show that by harnessing the multihop and multipath communication advantages, only a few user queries in a WSN can lead to an accumulation of accurate global knowledge at node level. This global knowledge can greatly improve numerous WSN applications when used in data validation, event detection, and query optimization