Express Server Architecture

The Express Server architecture consists of the following components:

• Clients
• The web server
• LizardTech services
• The image server
• Image data

Clients

You can access Express Server imagery from any Web Map Service (WMS) client. WMS is a widely-supported standard that you can use to view imagery from web browsers, from desktop GIS applications, from the ExpressZip web application included with Express Server, and more.

If you installed the optional JPIP component, then you can also access imagery from JPIP clients.

Web Server

Express Server works in conjunction with an existing web server installation to distribute imagery. Before you install Express Server, you must install either the Microsoft IIS web server on Windows or the Apache web server on Linux. On Windows, the IIS web server runs as a service called the World Wide Web Publishing service. On Linux, Apache runs as a daemon called httpd.

LizardTech Services

The following list describes the LizardTech services created during the installation of Express Server:

• Express Server Admin Backend Service. The Admin Backend service, or the Express Server Agent, processes requests from the Express Server Manager to start or stop the web server and perform licensing tasks. On Linux, the service runs as a daemon called ltagentd.
• Express Server Tomcat Service. The Tomcat service runs the Express Server web applications, including Express Server Manager for managing Express Server and ExpressZip for image-export. On Linux, the service runs as a daemon called lttomd.
• JPIP Service. The JPIP service is an optional service that you can add during the Express Server installation.The JPIP service processes requests from JPIP clients. On Linux, the service runs as a daemon called ltjpipd.

Image Server

The image server is the core of the Express Server installation that processes all image requests. When you connect to Express Server via WMS, the image server receives the image request and renders the image.

On Linux, the image server runs as a daemon known as ltcsd. On Windows, the image server runs as an application pool in IIS called LTESAppPool and does not require a dedicated service.

Image Data

You can store the image data that you want to distribute with Express Server on a local or network file system. Ensure that the image server and the LizardTech services have the correct permissions to access the image data, then use the Express Server Manager to configure the images that you want to distribute. For more information on permissions, see Permissions for Running Express Server.

How Express Server Works

Express Server's APIs represent an integration between the underlying Express Server engine and a supported Web Server, such as Apache or IIS. In addition to supporting its own web API, Express Server supports the OGC Web Map Service API (version 1.1.1) and, through the optional and separately installed JPIP Server, the JPEG 2000 Interactive Protocol, or JPIP, a protocol for progressively streaming imagery from a client to a server to support image use in bandwidth-constrained environments (for more information see Configuring the JPIP Server).

Express Server publishes collections of images, organized as "catalogs." The Express Server administrator defines all the catalogs in the Express Server Manager, a web-based administration interface. Generally, a catalog "points to" a directory on the server which contains images.

Each catalog contains folders and "items". These items are the images.

Because some images may be very very large, Express Server allows you to extract subsets of an image at various resolutions. In addition, Express Server can produce thumbnails of each image, in various sizes, and publish metadata contained in that image as XML. This means that a single image asset can serve for any number of croppings, scaled versions and scene subsets.

Express Server Features

Express Server outputs PNG (.png) and GIF (.gif) in addition to TIFF (.tif and .tiff), Windows Bitmap (.bmp) and JPEG (.jpg and .jpeg). MrSID (.sid), JPEG 2000 (.jp2), Geospatial PDF (.pdf) and NITF (.ntf) are supported as source file formats.

In addition to supporting its own web API, Express Server supports the OGC Web Map Service API (version 1.1.1). You can integrate Express Server image repositories with WMS-compliant geospatial data stores anywhere in the world. Integrate with diverse architectures and geospatial data while leveraging the world's best raster delivery technology. Also, in order to support WMS features, catalogs are by default automatically indexed for spatial query.