Image Server

The requirements for efficient distribution of ortophotography are ideally solved with the Cosylab Image Server, which has been developed as part of the Giselle LPIS system. The architecture consists of one central image server, many clients and an optional local image server, one for each LAN of clients. The local image server aggressively caches images and the central server ensures that the data are consistent and up to date. Images can be transferred either via the Internet, physically via DVD/CD, or both. The clients access the local image server for images. If an image is not cached yet, it is transparently loaded from the central image server to the local image server. The applied technology is similar to bitTorrent or other new generation P2P networks (such as KAD), which deal with the distribution of large data sets among many hosts.

The essential feature of the Cosylab Giselle Image Server, which similar systems lack, is that the central server manages both the images and the clients. A conventional architecture with independent clients installed on local machines would require maintenance and configuration efforts, license managements, etc. Other solutions such as terminal-host and Citrix would suffer heavy network performance penalties during peak load (i.e. all local clients accessing the images), because requests are not distributed and parallelized. This in turn would require a larger available bandwidth, although it would be idle most of the time. Even Citrix, which is optimized for screen transfer, must reload the complete image, if the pan operation is executed.

Our architecture ensures that no local IT managing expertise and effort is needed besides setting up a normal PC, thus keeping down long-term costs, often neglected by other solutions, which  tend to disregard long-term aspects and user satisfaction.

Cosylab Giselle Image Server supports local offices with the following features, designed to provide the best experience to end-users:

• Regional data pre-loading
• Distribution topology
• Configurable image transfer size and fidelity
• Local caching of retrieved data
• Smart Level-Of-Detail (LOD) processing

The presented design of the Image Server greatly improves performance of the system (compared to either accessing images from a central location or reading unprocessed images stored on local network file servers), while facilitating maintenance of the software infrastructure as well as that of the orthophotographic images. It is possible to update images in a central location, and the updates can automatically be distributed to local offices without the need for a local system administration.



Figure 1: Image server administration - The Server Administration Module includes tools for monitoring and management of the distributed image servers

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