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

International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004 Geo-Union Client Cache 2 Z1 Geo-Union Client. Geo-Union Client t = Network se N Cache =~ = ure Geo-Union - 2 - Spatial = = Client 2, Client = _ Database - i dd c Data Proxy Server. Cache t d Geo-Union| + Client Figure 2 Spatial Cache Framework Geo-Union Client Geo-Union Client (1) Cache for spatial database. Geo-Union server is the bridge between Geo-Union client and ORDB, so cache for spatial database is maintained by Geo-Union server. Cache is stored in both local file and memory. Because Geo-Union server can manage different spatial data resources, and also can reply different spatial data requests from different clients, so cache for spatial database is a global cache. (2) Network spatial cache. The bandwidth of different users in network is different, but public users of Internet always have low bandwidth. So when people use WebGIS applications, it is a lethal delay when spatial data is transferred from Geo-Union server. In Geo-Union client, we adopt a two-level spatial cache mode to relief transmission bottleneck of the network: The first network cache is used to help a single client access remote data: building a spatial cache in local place. This kind of cache is a partial cache, which is also a popular method in today's browser. The second network cache is used to help many clients in a LAN access remote data: building a common spatial cache for a LAN (cache server). Once a local client in the LAN accessed some spatial data, other clients can reuse the spatial data in cache server. Cache server is still a partial cache. Cache server can realize massive spatial data cache by means of the shared resources, which will speed up the hit rate of cache greatly, so as to improve efficiency of all local clients, and save resource of all local clients. Cache server solves the speed conflict between local disk data access and remote data access, and the speed conflict between the high-speed LAN and WAN with narrow bandwidth. (3) Spatial data proxy server. Because the distribution of users in Internet is not well-proportioned, so different Geo-Union servers are unbalanced. Some Geo-Union server and its communication may overload. Aiming to this problem, we design spatial data proxy server for those Geo-Union servers to improve performance. Spatial data proxy server is an initiative cache server. Overloaded Geo-Union server selects a suitable Geo-Union client and builds a spatial data proxy server there to response a special group of users. 202 In Geo-Union, spatial data proxy server serves as special server in Internet to provide spatial data access services for public users. The structure and implementation of spatial data proxy server is same as cache server, but they play a different role in Geo-Union. Cache server is private of a LAN, and clients in the LAN have to get an authorization before accessing to cache server. Spatial data in cache server is changing with different requests of clients in the LAN. Spatial data proxy server is public to all clients. Spatial data proxy server may serve as a peer of Geo-Union server. Spatial data proxy server can be built anywhere in Internet if needed. If spatial data in a spatial database is unchanged for a long time, spatial data proxy server can cache all spatial data of that spatial database. Building spatial data proxy servers properly in Internet will make Geo-Union applications more effective. 2.2 Organization of Spatial Cache In Geo-Union, spatial cache is organized as three levels: layer, slot and entity. When creating a layer in spatial database, a GUID (Global Universal Identification) is generated to identify the layer, which is named as /ayer/D. When reading a layer into cache, the system will allocate a separate space for the layer according to its /ayerID. Whether a layer is valid in cache is determined by the /ayerVersion of the layer both in cache and in spatial database. Entities in a layer are always separated into different slots according to a certain rule. When reading a layer into cache, we do not read the whole layer, but read some slots of the layer. Slot brings two benefits: almost all spatial queries do not need a whole layer but only a certain scope in the layer, so when the layer is massive, reading relative slots can satisfy the requirement and will reduce network load greatly; less data will exhaust less computing resource and storage resource. The rules to organize slot are various. We can organize slots in a layer according to a correlativity of geographical location or a neighborhood geographical location. 4A correlativity of geographical location means we can put entities along a railway into a slot, and a neighborhood geographical location means we will put entities in a certain spatial scope into a slot. Every entity in a layer belongs to a slot. When entities in any slots changed, the s/otVersion of the layer will change too. An update operation may modify only one or several entities in a layer, so /ayerVersion and slotVersion of the layer cannot reflect the latest modification of entities. We set a versionNumber for every entity, and when a entity changes, its versionNumber changes too. The entityVersion of a layer is the max versionNumber in the layer. When the versionNumber of a layer in cache is less than that in spatial database, some entities in cache is invalid and those entities that have larger versionNumber should be reloaded from spatial database into cache. 2.3 Refresh and Pro-load Spatial Cache Refreshment of spatial cache can be done online or offline. Online refreshment means updating spatial data in cache at the

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