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By R. Brian Culpepper, University of Arkansas Center for Advanced Spatial Technologies (www.cast.uark.edu), Fayetteville, Ark.

ArcGIS Image Server 9.2, ESRI’s most significant release for Earth imagery users, expedites cataloging, processing and distributing imagery and raster datasets via Image Services that can be modified on-the-fly with advanced server-side processing. The software offers a lot more functionality than a typical Web mapping system and shouldn’t be confused with ESRI’s ArcIMS product.

Processing Tools
The software’s architectural configuration includes the following components:
Image Server brokers the client requests, performs server-side imagery processing and then delivers the image to the client.

Service Providers perform image processing. This is where the real work is accomplished, so Service Providers should reside on the most capable computer available. This component can be scaled to handle heavy user loads by adding additional Service Providers that run on their own thread.
Image Services combine an archive of raw raster imagery with an Image Service Definition file (.ISDef) created/defined from within ArcGIS Desktop. Image footprints, bounding boxes and service overviews (pyramids) are created during the publishing process.

Service Editor tasks, which include the initial definition and creation of an Image Service, are handled within the ArcDesktop or ArcEngine application environments. An additional ArcGIS toolbar is added to existing desktop applications, providing access to the Image Service creation, modification and compiling commands.

Client applications are the final component, and there are several methods to freely access these published Image Services.

Image Server’s strength is its streamlined, multiformat image distribution capabilities for intranet consumers, but the same Image Services can be leveraged by ArcGIS Server applications, too. As a result, you can push large image services across your local area network and/or the Web.

The Image Server processing chain is where users can apply “on-the-fly” image processes to an Image Service, a group of raster datasets or a single image. There are 17 processes to choose from, including Pan-Sharpening, Convolution Filters, Image Stretching, Spectral Matrices, Image Algebra, Color Mapping, Pixel Classification, Band Extraction, NDVI Classification, Histogram Creation, Grayscale Conversion and Band Stacking, and Ortho Production.

ESRI also offers two Image Server extensions: an orthorectification extension to enhance out-of-the-box orthorectification processing and a seamline extension to generate and edit seamlines for overlapping image mosaics.

Ease of Installation
Image Server’s installation was a snap! To use the software’s Service Editor component, users are required to install the product over a licensed copy of ArcGIS 9.2 Desktop (ArcView, ArcEditor or ArcInfo) or ArcEngine 9.2 for developers. The 19-page installation guide is well written and easy to follow, particularly for such an impressive imagery distribution product. New users should go directly to the installation guide, as they will need the .NET 2.0 Framework and .NET Support for ArcGIS. These components are included on the install DVD.

I installed the software on a Windows XP machine with IIS 6.0 /.NET 2.0 and ArcInfo 9.2 already in place. I installed all of Image Server’s components on the same machine and accepted the default options throughout the entire process. There are also detailed instructions in the guide for each Image Server Client.

Viewer and Client Applications
The standalone Image Server Viewer is Windows NT/2000/XP-compatible client software included with ArcGIS Image Server 9.2 that enables remote connection and use of the published services. Additional application-specific clients are also delivered with Image Server:

• ArcGIS Desktop 9.1 and 9.2 (ArcMap, ArcGIS Server and ArcGlobe)

• MicroStation 8.1 and 8.5

• AutoCAD (versions 2000 through 2007)

There are some limitations with the 9.2 release of the Image Server Viewer. Users can’t view Image Services with more than three bands or greater than 8 bits, vector layers can’t be overlaid on an Image Service, and only one Image Service can be accessed, exported, saved or manipulated via the properties dialog with the viewer. However, the Image Server Viewer is useful for exploring Image Services, reviewing service properties and examining metadata related to a published service.

The client does allow properties such as the mosaic method, spatial reference system, resampling method, transmission compression and background color to be manipulated by the client user. All of these capabilities are useful because users can export an image to their local disk. The Image Server client enables the user to specify the spatial extent of the image to be exported as well as the format to be saved (TIFF, JPEG, JPEG 2000 and PNG), but the maximum volume and extent of the image data are controlled by the administrator/publisher of the Image Service.

Final Thoughts
Image Server would be an effective product for any application in which users need to quickly process and serve large volumes of geospatial imagery. For example, local government offices using high-resolution imagery would definitely benefit, as would photogrammetric/engineering/GIS professionals who acquire, access and use large raster datasets within AutoCAD, MicroStation, MapInfo or ArcGIS. The client viewers are free, and although the standalone viewer is a bit limited in functionality, the software-specific viewers are well integrated with their parent product. My colleagues and I were impressed with the speed of our Image Services during our evaluation—particularly because we installed the software on a modest desktop computer (1.7Ghz, 1GB RAM).

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