http://hdl.handle.net/10397/1220 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5197 Title: An assessment of shadow enhanced urban remote sensing imagery of a complex city - Hong Kong<br/><br/>Authors: Wan, Cheuk-Yan; King, Bruce Anthony; Li, Zhilin<br/><br/>Abstract: Large portions of shadowed areas in satellite images of urban areas can affect the accuracy of classification and thus reduce an image’s effectiveness in urban remote sensing applications. This is particularly acute in cities such as Hong Kong where dense high-rise buildings cast many long shadows across a variety of different surface types. One solution to this problem is to enhance shadowed areas so their spectral range becomes closer to their corresponding non-shadowed areas. Shadowed areas were automatically selected and two techniques, Gamma correction and Linear Correlation Correction, were applied to three study sites of a 2.4m Quickbird image. The selected study sites represent typical urban types of Hong Kong, ranging from high-rise commercial to low-rise residential areas. The shadow detection algorithm is based on the spectral shape index and its limitation is discussed. The histograms of the corresponding non-shadowed areas, the original and the enhanced shadow areas are used to compare the spectral range. The results show that the enhanced areas, in band ratios such as NDVI, show greater similarity after enhancement, but they also look darker than the non-shadowed areas. Where continuous shadowed areas such as in commercial areas, the spectral range cannot be restored. Sat, 25 Aug 2012 00:00:00 GMT http://hdl.handle.net/10397/5196 Title: Automatic construction of structured dentritic river networks<br/><br/>Authors: Zhang, L.; Guilbert, Eric<br/><br/>Abstract: The automated map generalization is always a challenging work in Geographical Information System (GIS). Regarded as terrain skeleton, drainage system should be considered in research on automated map generalization in the first place. Further, as the most important component of drainage system, generalization of rivers properly becomes a focal point. On land, rivers always connect together in networks, and most of these networks form tree structures. As a set of line features, river networks are generalized from large scale to small scale by two main steps: selective omission and selected rivers simplification. Before these steps, the structured dendritic river networks should be constructed. This paper puts forward an improved method of average direction based on angle of river network connections to detect the river flow and the main stream, and then create a data structure to store the topology relations of tributaries in the river networks. Eventually, the paper gives a comparative analysis with existed methods on river flow detecting and topology relation building.<br/><br/>Description: The 3rd International Postgraduate Conference on Infrastructure and Environment is organized by the Faculty of Construction & Land Use of The Hong Kong Polytechnic University on 11 and 12 July 2011 in Hong Kong. Fri, 01 Jul 2011 00:00:00 GMT http://hdl.handle.net/10397/5195 Title: A conceptual model for submarine feature description and generalisation in nautical chart production<br/><br/>Authors: Yan, Jingya; Guilbert, Eric; Saux, Eric<br/><br/>Abstract: This paper aims at defining an ontology of the nautical chart generalisation process that will be at the root of a model oriented generalisation process.<br/><br/>Description: The conference is co-organized by Institute of Space and Earth Information Science, The Chinese University of Hong Kong, National Remote Sensing Center of China and The International Association of Chinese Professionals in Geographic Information Sciences (CPGIS). Sun, 17 Jun 2012 00:00:00 GMT http://hdl.handle.net/10397/4617 Title: Assessing the stability of the new marine DGPS station of Hong Kong and its connection to the WGS84 datum<br/><br/>Authors: Iz, H. Bâki; Chen, Yong-qi; Wang, Jiexian<br/><br/>Abstract: The permanent DGPS station of Marine Department, located on Kau Yi Chau Island in Hong Kong, has begun its operation in 1996. One of the factors which affects the quality of the differential corrections generated by the station is the accuracy of its reference coordinates in the WGS84 datum. Although the station is positioned over one of the existing trigonometric stations of Hong Kong datum whose position is also known in the WGS84 datum, the accuracy of the known coordinates needs to be verified independently. We have used two months data to calculate repeated baselines from this station to five IGS core stations located in China, namely, Wuhan, Shanghai, Xian, Lhasa, and Taiwan using the GAMIT software. Sub-centimeter rms baseline error has been demonstrated during this period. These results indicate stability of GPS measurements over a long period of time well beyond expectations. We have used the estimated baseline vectors to connect Kau Yi Chau station to the ITRF94 and subsequently to the WGS84 datum. Preliminary results indicate centimeter and decimeter level agreement in latitude and longitude between the known reference coordinates and the ones derived from ITRF-94 connection. We have observed, however, over three meters of discrepancy in height. Fri, 01 Aug 1997 00:00:00 GMT