We present a new algorithm for appearance-preserving simplification. Not only does it generate a low-polygon-count approximation of a model, but it also preserves the appearance. This is accomplished for a particular display resolution in the sense that we properly sample the surface position, curvature, and color attributes of the input surface. We convert the input surface to a representation that decouples the sampling of these three attributes, storing the colors and normals in texture and normal maps, respectively. Our simplification algorithm employs a new texture deviation metric, which guarantees that these maps shift by no more than a user-specified number of pixels on the screen. The simplification process filters the surface position, while the runtime system filters the colors and normals on a per-pixel basis. We have applied our simplification technique to several large models achieving significant amounts of simplification with little or no loss in rendering quality.

XML documents are typically queried with a combination of value search and structure search. While querying by values can leverage traditional database technologies, evaluating structural relationship, specifically parent-child or ancestor-descendant relationship, between XML element sets has imposed a great challenge on efficient XML query processing. This paper proposes XR-tree, namely, XML Region Tree, which is a dynamic external memory index structure specially designed for strictly nested XML data. The unique feature of XR-tree is that, for a given element, all its ancestors (or descendants) in an element set indexed by an XRtree can be identified with optimal worst case I/O cost. We then propose a new structural join algorithm that can evaluate the structural relationship between two XR-tree indexed element sets by effectively skipping ancestors and descendants that do not participate in the join. Our extensive performance study shows that the XR-tree based join algorithm significantly outperforms previous algorithms. 1.

A compact color descriptor and an efficient indexing method for this descriptor are presented. The target application is similarity retrieval in large image databases using color. Colors in a given region are clustered into a small number of representative colors. The feature descriptor consists of the representative colors and their percentages in the region. A similarity measure similar to the quadratic color histogram distance measure is defined for this descriptor. The representative colors can be indexed in the three-dimensional (3-D) color space thus avoiding the high-dimensional indexing problems associated with the traditional color histogram. For similarity retrieval, each representative color in the query image or region is used independently to find regions containing that color. The matches from all of the query colors are then combined to obtain the final retrievals. An efficient indexing scheme for fast retrieval is presented. Experimental results show that this compact descriptor is effective and compares favorably with the traditional color histogram in terms of overall computational complexity. Index Terms---Color indexing, dominant color feature, regionbased retrieval. I.

Abstract—The skyline of a multidimensional data set contains the “best ” tuples according to any preference function that is monotonic on each dimension. Although skyline computation has received considerable attention in conventional databases, the existing algorithms are inapplicable to stream applications because 1) they assume static data that are stored in the disk (rather than continuously arriving/expiring), 2) they focus on “one-time ” execution that returns a single skyline (in contrast to constantly tracking skyline changes), and 3) they aim at reducing the I/O overhead (as opposed to minimizing the CPU-cost and main-memory consumption). This paper studies skyline computation in stream environments, where query processing takes into account only a “sliding window ” covering the most recent tuples. We propose algorithms that continuously monitor the incoming data and maintain the skyline incrementally. Our techniques utilize several interesting properties of stream skylines to improve space/time efficiency by expunging data from the system as early as possible (i.e., before their expiration). Furthermore, we analyze the asymptotical performance of the proposed solutions, and evaluate their efficiency with extensive experiments. Index Terms—Skyline, stream, database, algorithm. 1

Uncertainty pervades many domains in our lives. Current real-life applications, e.g., location tracking using GPS devices or cell phones, multimedia feature extraction, and sensor data management, deal with different kinds of uncertainty. Finding the nearest neighbor objects to a given query point is an important query type in these applications. In this paper, we study the problem of finding objects with the highest marginal probability of being the nearest neighbors to a query object. We adopt a general uncertainty model allowing for data and query uncertainty. Under this model, we define new query semantics, and provide several efficient evaluation algorithms. We analyze the cost factors involved in query evaluation, and present novel techniques to address the trade-offs among these factors. We give multiple extensions to our techniques including handling dependencies among data objects, and answering threshold queries. We conduct an extensive experimental study to evaluate our techniques on both real and synthetic data. 1.

this paper we present probabilistic cost models that estimate the selectivity of spatio-temporal window queries and joins, and the expected distance between a query and its nearest neighbor(s). Our models capture any query/object mobility combination (moving queries, moving objects or both) and any data type (points and rectangles) in arbitrary dimensionality. In addition, we develop specialized spatio-temporal histograms, which take into account both location and velocity information, and can be incrementally maintained. Extensive performance evaluation verifies that the proposed techniques produce highly accurate estimation on both uniform and non-uniform data

In an uncertain database, every object o is associated with a probability density function, which describes the likelihood that o appears at each position in a multidimensional workspace. This article studies two types of range retrieval fundamental to many analytical tasks. Specifically, a nonfuzzy query returns all the objects that appear in a search region rq with at least a certain probability tq. On the other hand, given an uncertain object q, fuzzy search retrieves the set of objects that are within distance εq from q with no less than probability tq. The core of our methodology is a novel concept of “probabilistically constrained rectangle”, which permits effective pruning/validation of nonqualifying/qualifying data. We develop a new index structure called the U-tree for minimizing the query overhead. Our algorithmic findings are accompanied with a thorough theoretical analysis, which reveals valuable insight into the problem characteristics, and mathematically confirms the efficiency of our solutions. We verify the effectiveness of the proposed techniques with extensive

Recent growth of the geo-spatial information on the web has made it possible to easily access a wide variety of spatial data. By integrating these spatial datasets, one can support a rich set of queries that could not have been answered given any of these sets in isolation. However, accurately integrating geo-spatial data from different data sources is a challenging task. This is because spatial data obtained from various data sources may have different projections, different accuracy levels and different formats (e.g. raster or vector format). In this paper, we describe an information integration approach, which utilizes various geo-spatial and textual data available on the Intemet to automatically annotate and contlate satellite imagery with vector datasets. We describe two techniques to automatically generate control point pairs from the satellite imagery and vector data to perform the conflation. The first technique generates the control point pairs by integrating information from different online sources. The second technique exploits the information from the vector data to perform localized image-processing on the satellite imagery. Using these techniques, we can automatically integrate vector data with satellite imagery or align multiple satellite images of the same area. Our automatic conflation techniques can automatically identify the roads in satellite imagery with an average error of 8.61 meters compared to the original error of 26.19 meters for the city of E1 Segundo and 7.48 meters compared to 15.27 meters for the city of Adams Morgan in Washington, DC.

Geometric coordinates are an integral part of many data streams. Examples include sensor locations in environmental monitoring, vehicle locations in traffic monitoring or battlefield simulations, scientific measurements of earth or atmospheric phenomena, etc. How can one summarize such data streams using limited storage so that many natural geometric queries can be answered faithfully? Some examples of such queries are: report the smallest convex region in which a chemical leak has been sensed, or track the diameter of the dataset. One can also pose queries over multiple streams: track the minimum distance between the convex hulls of two data streams; or report when datasets A and B are no longer linearly separable. In this paper, we propose an adaptive sampling scheme that gives provably optimal error bounds for extremal problems of this nature. All our results follow from a single technique for computing the approximate convex hull of a point stream in a single pass. Our main result is this: given a stream of two-dimensional points and an integer r, wecan maintain an adaptive sample of at most 2r +1pointssuch that the distance between the true convex hull and the convex hull of the sample points is O(D/r 2), where D is the diameter of the sample set. With our sample convex hull, all the queries mentioned above can be answered in either O(log r) orO(r) time. 1

This paper provides a model that realistically represents the movements in a disaster area scenario. The model is based on an analysis of tactical issues of civil protection. This analysis provides characteristics influencing network performance in public safety communication networks like heterogeneous area-based movement, obstacles, and joining/leaving of nodes. As these characteristics can not be modelled with existing mobility models, we introduce a new disaster area mobility model. To examine the impact of our more realistic modelling, we compare it to existing ones (modelling the same scenario) using different pure movement and link based metrics. The new model shows specific characteristics like heterogeneous node density. Finally, the impact of the new model is evaluated in an exemplary simulative network performance analysis. The simulations show that the new model discloses new information and has a significant impact on performance analysis.