Time filter

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Portland, OR, United States

Kima J.,800 Airport Center Dr Ste 102 | Park B.,University of Virginia | Leeb J.,University of Virginia | Won J.,PTV America Inc.
Engineering Applications of Artificial Intelligence | Year: 2011

Travel time is the most intuitive measure of effectiveness for road users and transportation agency operators. However, travel times derived from speed data measured at fixed point sensors often varies from actualtravel time. This is,inpart, due to the intentional positioning of sensorsto avoid lane changing and/orto inadequate numbersof sensors capturing the dynamiccharacteristics inherent infreeway traffic flow. This paper presents an approach that optimizes the location of sensors in a freeway to support more accurate estimations of travel times than those obtained from conventionally deployed fixed point sensors. Evaluation results, under varying traffic conditions, including incidents, showed that the proposed approach produced average travel time estimation errors within 10% and performed much better than the conventional approach. Thus, the proposed approach provides a promising tool tosupport re-positioning of the existing non-intrusive point sensors (e.g., video sensors) or deployment of new sets of point sensors for improving travel time estimation. © 2010 Elsevier Ltd. All rights reserved. Source

Liu L.,Beijing Normal University | Zhang L.Q.,Beijing Normal University | Ma J.T.,PTV America Inc. | Zhang L.,Beijing University of Civil Engineering and Architecture | And 3 more authors.
Science China Information Sciences | Year: 2010

This paper presents an efficient method for implementing visibility analysis on complex landscapes based on an improved LOS (line of sight) algorithm. The method determines the viewshed by analyzing the geometric relationship between the target points and viewpoint. It differentiates the visibility of the target points by the elevation information. Eventually the visual results related to the given viewpoint are rendered on three-dimensional landscapes. The visibility of some target points is computed by comparing their elevations with the viewpoint's height, thus is able to enhance the efficiency of the visibility analysis. This method can not only be applied in the visibility analysis of forest scenes, but also used in the analysis of the urban environment. Experiments show that the proposed method results in high efficiency and precision. © Science China Press and Springer-Verlag Berlin Heidelberg 2010. Source

Chen C.,Beijing Normal University | Zhang L.,Beijing Normal University | Ma J.,PTV America Inc. | Kang Z.,University of Science and Technology of China | And 2 more authors.
International Journal of Geographical Information Science | Year: 2010

Labeling plays an important role in map production, attaching specific texts to related geographic elements to provide clear environmental references. In three-dimensional geographical information systems (3DGISs), however, cluttering happens fairly commonly because of the unexpected overlapping and occlusion among labels and related objects, and results in an ambiguous and obscure environment. It generally also takes large computing power and memory to visualize spatial entities. Aimed at both unambiguous and efficient 3D map display, this article proposes an adaptive multi-resolution labeling method to deal with point, polyline, and polygon features labeling in a 3D landscape. It implements adaptive placement and view-driven label filtering without obscuring other visual features. The experiments indicated that the display of overlapping labels and label popping are reduced significantly with less computation burden while retaining the rendering quality. © 2010 Taylor & Francis. Source

Deng H.,Beijing Normal University | Deng H.,Central South University | Zhang L.Q.,Beijing Normal University | Mao X.C.,Central South University | And 5 more authors.
Science China Earth Sciences | Year: 2010

In the application of 3D Geoscience Modeling, we often need to generate the volumetric representations of geological bodies from their surface representations. Linear octree, as an efficient and easily operated volumetric model, is widely used in 3D Geoscience Modeling. This paper proposes an algorithm for fast and dynamic generation of linear octrees of geological bodies from their surface models under hardware acceleration. The Z-buffers are used to determine the attributes of octants and voxels in a fast way, and a divide-and-conquer strategy is adopted. A stack structure is exploited to record the subdivision, which allows generating linear octrees dynamically. The algorithm avoids large-scale sorting process and bypasses the compression in linear octrees generation. Experimental results indicate its high efficiency in generating linear octrees for large-scale geologic bodies. © Science China Press and Springer-Verlag Berlin Heidelberg 2010. Source

Deng H.,Beijing Normal University | Zhang L.,Beijing Normal University | Ma J.,PTV America Inc. | Kang Z.,University of Science and Technology of China
Computers and Geosciences | Year: 2011

In 3D terrain navigation applications, the views based on general perspective projection often find features of interest (FOIs) being occluded. As an alternative, panorama-like views preserve the similarity between 3D scenes before and after the deformations while ensuring the visibility of interested features. In this paper, an automatic method for generating panoramic map-like views is proposed in mountainous areas. The created panorama-like views by moving up the view position as well as the terrain deformation can successfully avoid occlusions of the FOIs. The final views also ensure the resemblance in appearance for the FOIs and landscapes, and thus satisfy the demand for interactive occlusion-free navigation in 3D complex terrain environments. © 2011 Elsevier Ltd. Source

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