Portal Technology
The state of Washington's Imagery Portal provides access to a growing collection of ortho photography. Public access to the imagery is provided through a web application accessible through www.geography.wa.gov/ImageExtractor/Default.aspx. This document provides a brief overview of the technologies supporting this application.

The Portal is built on Environmental Systems Research Institute's (ESRI) ArcGIS Server technology. Two servers compose the computing environment. The image server manages access to the collection of imagery. The application server hosts the web application and web server. Both servers are built on MicroSoft's Windows Server operating system with MicroSoft's Internet Information Services (IIS) supporting web services on the application server.

Using the web application, users interact directly with the application server which makes requests for images to the image server. The web application is built from simple out of the box components shipped with ArcGIS Server Standard Enterprise Edition and custom components built using Microsoft's C#.net programming language. The primary custom component, the 'clip and ship' application, allows users to extract subsets of imagery in a wide array of image formats and coordinate systems. To improve performance while browsing, the web application makes use of 'cached' images. Caching combines orthoimagery, public land survey boundaries, geographic names, and other layers in a set of pre-generated, statewide, composite images, each one being tuned or generalized to display very quickly within a specific range of map scales. In exchange for the faster display, the user does not have the ability to control what layers are displayed. Caching also limits how far a user can zoom into the imagery. High resolution source imagery is accessed only by the 'clip and ship' application.

The Image Server provides a flexible environment for the management, processing and distribution of diverse sets of imagery. Services available on the server can deliver different imagery with different formats, resolutions, color schemes, or projections. The image source can be a single image or composed of overlapping or non-overlapping collections. The National Agriculture Imagery Program (NAIP) imagery from 2006, which is available through the Portal, is composed of 14,088 non-overlapping compressed (5:1) tiles consuming approximately 700 GB of disk space. Tiles are mosaiced on the fly as the web application or other clients request an image. Image Server supports a wide array of image formats including TIFF, PNG, JP2000, and JPEG. Imagery is stored as simple file objects in a standard Windows directory structure. State agencies have direct access to services available directly through the Image Server for use in agency developed and hosted interactive mapping applications.

Read more about the technology used in the Washington Image Portal by visiting these web sites:
ArcGIS Server: http://www.esri.com/software/arcgis/arcgisserver/index.html
ArcGIS Server Image Extension: http://www.esri.com/software/arcgis/serverimage/index.html

 

Return to Portal Home Page | Link to Image Viewer/Extractor | Help page