ArcGIS Image Server stand-alone architecture
Legacy:ArcGIS 10 is the last release of the stand-alone ArcGIS Image Server product. The image service definition (.ISDef) has been replaced by an improved geodatabase data model—the mosaic dataset—which can be published as an image service using the ArcGIS Server Image extension.
The ArcGIS Image Server architecture contains several components, which are organized into three main parts:
- Image server—This acts as the request broker between clients and the processing component that provides data to the client.
- Service provider—This is the processing component that processes image service components and distributes data to the client.
- Image service—This is the image service definition and a collection of rasters to be served.
An image server administrator defines and manages the various ways in which the main parts of ArcGIS Image Server are created and work together. The administrator uses Service Editor in ArcMap to create the image service definition. The Server Manager application is used by the administrator to run the image server, manage the services and their service providers, and control server configuration and access.
The diagram below outlines the Image Server architecture:
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ArcGIS Image Server components
Raster data
An image service supports a number of raster datasets as raster types, such as QuickBird Basic, QuickBird Standard, Landsat ETM 1G, TIFF, United States Geological Survey (USGS) digital orthophoto quadrangle (DOQ), and USGS digital elevation models (DEM). Generally, for every raster data type, there is associated metadata, either as a header or as part of an associated file. This metadata can contain basic information about the raster, such as its coordinate system, pixel size, number of rows and columns, and number of bands. Metadata can also include more detailed information, such as the date of acquisition, cloud cover, and data provider's name. The raster data and any associated files should be stored together or in the same file/folder structure as the data exists in when provided from a data vendor. For example, .tif files using the information in a world file should have the .tfw file stored in the same folder.
Raster data for ArcGIS Image Server can be stored on a local disk, on a removable disk drive, or in a database; raster data can be stored anywhere, as long as it can be readily accessed by ArcGIS Image Server. The speed of reading the data affects the performance.
Image service definition
The image service definition (.ISDef) file contains all the information used to create the image service. It references the raster data that is going to be served; defines the properties of the service, such as the spatial reference and metadata; defines the image-processing steps that will be applied to the raster data; and defines information about the output image rendering, presentation, and properties, such as the mosaic order and which images will display at what resolutions.
Links to the raster data from the image service definition are found in a raster process definition (.RPDef) file, which contains specific information about each raster dataset used in the image service, such as the pixel size, spatial reference, and extent.
The image service definition is created and edited in ArcMap using tools on the Image Service Editor toolbar. The image service definition appears in ArcMap as a custom layer containing one to four of the following layers:
- The footprint layer outlines the displayable extent of each raster dataset (and defines the extent of the raster data, which is used to create the mosaicked image).
- The boundary layer outlines the extent of all the datasets as a whole.
- The preview layer is used to display the service once it is built.
- The seamline layer allows advanced capabilities in defining boundaries and specific rules that will be applied when mosaicking the raster data.
The image service definition exists as a folder containing the footprint shapefile, a service table that is part of the footprint shapefile, a boundary shapefile, the ImageService.ISDef, a subfolder with the raster process definitions, and a seamline shapefile (if it is created). These contents are compiled to create the image service file that is used by the service providers, with the extension .ISCDef.
Image service
An image service is defined by the image service definition file and the collection of raster data that is compiled and saved to a file with the extension .ISCDef. The service provider uses this file to generate the image service data that is accessed by the clients.
Service provider
The service provider is the workhorse of the system, and multiple service providers can be running within the ArcGIS Image Server system. Service providers receive the requests from the client applications for an image service product, perform the processing outlined in an image service, and deliver the required data to the client.
These are the main functions of the service provider:
- Maintain one or more image services.
- Communicate with the specified image server.
- Communicate with the clients that require access to the imagery.
- Provide and process streams of image data in reply to client requests.
- Maintain a detailed log of all the imagery requests made.
Service providers can serve one or more image services—they usually contain a list of image services that a client can choose to receive. For example, you could have many image services on one service provider when you want to provide multiple products from one raster data source, such as Landsat. With Landsat, you could provide multiple image services of different band combinations or a normalized difference vegetation index (NDVI) image service, and if you have an elevation model, you may want to generate derived products such as color-coded elevation models or shaded relief models to be used in conjunction with the Landsat data. The same image service can be hosted by more than one service provider as well. You may need to do this when a particular image service is requested often.
The image server scales to support heavier loads by using additional service providers. The service provider's architecture is multithreaded. Therefore, each request runs in its own thread, and a request can be for any one of the image services it's providing. Multiple service providers can run in parallel, and each service provider can work with multiple image services.
When a valid client connection for an image service is received, the service provider creates a connection that it maintains until the client disconnects or is timed out. Requests are made from the client to the service provider for imagery. The service provider processes the image service and returns the requested imagery to the client. Summary details about the connections are sent to the image server on disconnect or at periodic intervals.
Image server
The image server publishes the available image services, acts as an image service request broker, ensures that users have the rights to access image services, and provides load balancing between service providers. Client applications make their first contact through the image server, and the image server identifies the service provider with which the client will further communicate.
The main functions of the image server are the following:
- Maintain a list of all the available image services.
- Provide details of available image services to client applications.
- Authenticate clients and provide access control to the image services.
- Perform load balancing when an image service is available on multiple service providers.
- Provide the client application with the appropriate connection details to connect to an allocated service provider.
- Maintain a log of all the connections made.
The image server is managed by the Server Manager application; see About managing the image servers.
ArcGIS Image Server tools
The tools that are part of the ArcGIS Image Server application include the administration tools and client applications. The administration tools are used by people to build the image service definitions and by people who will administer the image server—these include Service Editor (through the Image Service Definition Editor toolbar) in ArcMap and the stand-alone Server Manager application.
Service Editor
Image service definitions are created and edited in ArcMap using the tools and functions on the Image Service Definition Editor toolbar.
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The Image Service Definition Editor toolbar is used to do the following:
- Create a new image service definition and define its properties.
- Add or remove raster data.
- Define any processing that is to be applied to all the data in the image service definition or to individual rasters.
- Build the image service definition.
- Review the image footprints and edit any seamlines.
- Preview the image service definition image.
- Validate the processes and data in the image service definition.
- Optimize the image service definition by creating derived tiles and overviews.
- Generate the compiled image service definition files (.ISCDef) used by the service providers.
Server Manager application
An administrator uses the Server Manager application to manage the image server, service providers connected to the image server, and image services published by each service provider. There are tools in this application that allow an administrator to perform these tasks:
- Configure the image server and service providers.
- View the status of and start and stop the image servers, service providers, and image services.
- Synchronize a modified image service on a service provider.
- Export or review log files.
- Manage security.
Client applications
Image Server supports the following applications:
- ArcGIS (9.1 to 10) applications: ArcMap, ArcGlobe, ArcIMS, and ArcGIS Server
- AutoCAD
- MicroStation
- GeoMedia
- MapInfo
- Image Server Viewer, a free viewer that is delivered as part of ArcGIS Image Server
By installing some additional free software, you can access the published image services from the image server directly from your desktop applications. In ArcMap, for example, a tool that is added to the user interface through the Customize dialog box allows ArcMap to access image services as a client. These client applications allow you to directly change some of the image properties, such as the spatial reference, compression, and mosaic method of the image data you receive. They also allow you to view associated metadata and export the image data to a file.