Proceedings, XXth congress: Proceedings, XXth congress

Altan, M. Orhan

Bibliographic data

Multivolume work

Persistent identifier:: 1663674213

Title:: Proceedings, XXth congress

Sub title:: Istanbul, 12 - 23 July 2004

Year of publication:: 2004

Place of publication:: Istanbul

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 1663674213

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist aus dem Copyrightjahr ermittelt.; Auch bezeichnet als XXth International Congress for Photogrammetry and Remote Sensing

Editor:: Altan, M. Orhan

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing, Commission Primary Data Acquisition

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing, Commission Primary Data Acquisition

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing, Commission Primary Data Acquisition

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing, Commission Primary Data Acquisition

Document type:: Multivolume work

Volume

Persistent identifier:: 166368779X

Title:: Proceedings, XXth congress

Scope:: IV, 226 Seiten

Year of publication:: 2004

Place of publication:: Istanbul

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 166368779X

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(35,B8)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist aus dem Copyrightjahr ermittelt.

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Altan, M. Orhan

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 20., 2004, Istanbul; International Society for Photogrammetry and Remote Sensing

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: DESIGN SPATIAL CACHE FOR WEBGIS LUO Yingwei, WANG Xiaolin and XU Zhuoqun

Document type:: Multivolume work

Structure type:: Chapter

2004 rver blic OXY e in lave atial s of data atial d. If ime, atial will yer, obal yer, che, ding ined atial slots , We yer. eda the the will ules ayer Fr a of way ; we very slots 's in nnot ( 3 ;, its ; the of a ities rger into line. t the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004 same time as updating spatial entities in a layer in spatial database. Offline refreshment means updating invalid spatial data of a layer in cache if their versions are invalid when accessing to them. Information in spatial cache includes /ayerVersion, slotVersion, entityVersion and the corresponding relations between all entities and slots of a layer. When accessing to entities in a layer, we can determine whether spatial data in cache is valid or not through comparing version information in cache and spatial database. (1) If /ayerVersion of a layer in cache is smaller than that in spatial database, it means that all entities of the layer are changed, and the whole layer should be refreshed in cache. Otherwise, (2) If slotVersion of a layer in cache is smaller than that in spatial database, it means that all slots of the layer are rearranged, and the corresponding relations between all entities and slots of the layer should be refreshed in cache. Otherwise, (3) If entityVersion of a layer in cache is smaller than that in spatial database, it means that some entities of the layer are changed, and those entities should be refreshed in cache. (4) If above three conditions are all equal to those in spatial database, it means spatial data of a layer in cache is same as that in spatial database, and no refreshment is required. When accessing to spatial data, if we can pre-load some spatial data into cache, it will make spatial cache more effective. But how to predict what kind of spatial data will be accessed to? There are two rules of accessing to memory: there is every probability of accessing to just being accessed memory, and there is every probability of accessing to neighbors of just being accessed memory. There are same rules in accessing to spatial data: there is every probability of accessing to just being accessed spatial data, and there is every probability of accessing to neighbors of just being accessed spatial entities. According to those rules, we can arrange slots by spatial scope, and a slot is an accessing unit of spatial data. When the network is idle, we can pre-load some neighbors of spatial data in cache from spatial database. 3. CONCLUSIONS Geo-Union has finished a preliminary component-based model for distributed WebGIS, and has got into use in many fields with sound effects. Although spatial cache and other techniques are adopted in Geo-Union to improve its performance, a lot of works still wait us ahead to make Geo-Union more practicable and effective: (1) Dynamic load balancing policy. In Geo-Union, most works are completed at client side, and server is only responsible for data access and simple data query. Therefore it is not well balanced between client and server. Especially there will exists a lot of transmission for massive data between client and server. Although, spatial index and spatial cache techniques can improve the performance to a certain extent, we still want to take full advantage of the computing capability of GIS server, so as to lighten load at client side and decrease the transmission 203 of redundant data in network. This needs a more reasonable component design for the system. (2) System concurrency. WebGIS is open to millions of users. How to ensure the correctness, validity, stability and scalability of Geo-Union to satisfy users’ requests is another key problem for practicable WebGIS. 4. ACKNOWLEDGEMENT Supported by the National Grand Fundamental Research 973 Program of China under Grant No.2002CB312000; the National Research Foundation for the Doctoral Program of Higher Education of China under Grant No. 20020001015; the National Science Foundation of China under Grant No.60203002; the National High Technology Development 863 Program under Grant No. 2002AA 135330 and No. 2002AA 134030: the Beijing Science Foundation under Grant No.4012007. 5. REFERENCES Li Bin, 2001. A Component Perspective on Geographic Information Services. — Cartography and Geographic Information Science, 27(1), pp.75-86. Dept. of Computer Science and Technology, Peking University, 2002. Operation and Component Guide for Geo-Union Enterprise (in Chinese). Technology Material, http://gis.pku.edu.cn. (accessed 20 Oct. 2002).

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