About serving raster data
Last modified April 13, 2010
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This topic was updated for 9.3.1.
Raster data can be served as part of a map document or globe document, from a raster dataset or layer, from an image service definition, or from a geodatabase. It is served using ArcGIS Server and optionally using the ArcGIS Image Server extension.
There are several ArcGIS services including a map service, image service, geocoding service, geoprocessing service, geodata service, and globe service. They have varying capabilities that may include network analysis and mobile, and they have associated ArcGIS services such as geoprocessing and geodata. They all have Web connections depending on the service type (using open standards and protocols) such as WMS, WCS, and OGC Web Feature Service (WFS).
Raster data can and has traditionally been served as a layer in many of these services by adding a raster dataset layer to the map document or globe document, then publishing it. With the geodata service, a geodatabase containing raster datasets can be published with WCS capabilities. Raster catalogs contained in the geodatabase will be ignored, therefore not served. With the addition of the image service, raster data can be served on its own with imaging, WMS, or WCS capabilities.
Learn more about service capabilities and raster data.
An image service provides access to raster data through a Web service. The source of the raster data can be a raster dataset (from a geodatabase or file on disk), a raster dataset layer, or a compiled image service definition (containing one or more raster datasets and defined processes) created using ArcGIS Image Server. An image service will always be served with imaging capabilities; however, a user can also choose to serve it with WMS or WCS capabilities.
NOTE: Raster catalogs cannot be served as an image service.
When you publish an image service, you can choose up to three service capabilities. Additionally, the different sources for an image service result in slightly different capabilities and affect the layer properties.
An image service served with imaging capabilities is designed for the GIS Web server architecture and is similar to the mapping capabilities of a map service. It can host any type of raster dataset, raster dataset layer, or compiled image service definition. When you publish an image service, the imaging capability is always enabled. Users can connect to these image services via the Add ArcGIS Server connection by entering a universal resource locator (URL) such as an http address or by providing a LAN address such as the name or IP address of a computer. Users can also make a direct connection using any of the client applications provided with the ArcGIS Image Server extension (and only if a compiled image service definition has been published). For this they will need the IP address or computer name and port information for the server. Additional layer properties will be available if a compiled image service definition has been published including allowing users to change the mosaicking options and providing specific metadata. When an image service is opened within ArcGIS, it is treated like any other raster datasets; for example, there are renderers that are used to display the data, and the data can be used as input for a geoprocessing tool.
Learn about adding an image service layer to ArcMap.
Learn about the image service layer properties.
An image service served with the OGC WCS capabilities has many of the imaging capabilities. It can host any type of raster dataset, raster dataset layer, or compiled image service definition. A user can connect to a WCS service via the Add WCS Server connection in ArcGIS Desktop, through a web application, or using other applications that consume WCS. The layer properties of the imaging and WCS image services are the same, but the raster is rendered on the client side, unlike the imaging service where the server renders the raster data. Therefore, the values transmitted are the raw data values, thus, the image service can be used as input for analysis or display. For example, a WCS image service layer can be used in a geoprocessing model, or used to generate the surface in the ArcGlobe application.
Learn about adding a WCS service layer to ArcMap.
An image service served with the OGC WMS capabilities will have similar functionality to other WMS services. You can serve a raster dataset directly with WMS capabilities; you do not need to create a map document containing a raster dataset layer. An image service served as a WMS service will contain only one layer since it represents one input. A user can connect to a WMS service via the Add WMS Server connection in ArcGIS Desktop, through a Web application, or using other applications that consume WMS. When the raster data is served using WMS, it is rendered by the server and delivered to the consumer as a picture with coordinates. Users will not have the functionality to change any of the properties of the data delivered via the WMS. When publishing raster data using WMS, the image service is limited to grayscale or RGB color images, which are provided by rendering a single-band (grayscale), a single-band with a color map, or three-band combination. By default, a raster dataset will be served with the default layer settings (and band combinations). Additionally, the data will be resampled to an 8-bit image.
Learn about adding a WMS service layer to ArcMap.
|Raster data sources||
|User connection||-ArcGIS Server via URL or LAN
|Exporting||ArcGIS Server connection (such as ArcMap)
|ArcGIS Server connection (such as ArcMap)
There are many things to consider when you are preparing to create an image service because not all raster data will be served in an equal manner depending on the capabilities you choose.
Is there one dataset or many raster datasets?
If you have a single raster dataset that you want to serve, such as a mosaicked raster dataset in SDE or a large DEM, then ArcGIS Server is capable of handling this; however, if you need to serve many raster datasets that will compose a single image service, or you want to serve up many raster datasets that overlap completely and were captured at various dates or times that will compose a single image service, you will have to create an image service definition with the Image Service Definition Editor toolbar (provided with the ArcGIS Image Server extension) in ArcMap first. A raster catalog cannot be served as an image service; however, if the raster catalog is unmanaged, you can easily point to the folder or folders containing the source data and create an image service definition that can be served as an image service.
Is the raster data for viewing as an image or as input for analysis?
If the users of the image service will not be making adjustments to the appearance of the image, other than adjusting things like transparency, brightness, and contrast, and will not be using the raster data as input for any analysis, then this data can be served with any of the capabilities. If the user will be accessing the data in the image service to do further analysis, such as spatial analysis with the geoprocessing tools, or generating a surface from elevation data, then the image service will have to be served with the imaging and WCS capabilities.
Does the data have multiple bands or need to be enhanced?
The layer properties of a WCS or imaging image service will allow the user to change the band combination or apply a stretch to the histogram to enhance the appearance of the image. If serving a raster dataset using WMS, the user will not be able to change the rendering or the band combination, therefore, a raster dataset layer or an image service definition are the preferred inputs for a WMS service. If a raster dataset is served using the WMS capabilities, the default raster display settings will be applied. If an image service definition is used, the output properties need to be defined as 3-band color (RGB) or 1-band grayscale.
Learn about the default raster display settings.
Is any processing required?
When you serve a raster dataset or raster dataset layer, the raster dataset must be in its final state and ready for the user to use. However, when you publish an image service definition, processing can be defined that will be applied by the server on the fly, for example, orthorectification, enhancements, band combinations, band algebra, pan-sharpening, and filtering.
There are two options for publishing image services—using ArcGIS Server (to publish raster datasets and raster dataset layers) and optionally using the ArcGIS Image Server extension (to publish compiled image service definitions). You can use ArcGIS Image Server without ArcGIS Server, but then you can only publish compiled image service definitions. It also changes how users will connect to the data.
NOTE: You can only publish compiled image service definitions if you have ArcGIS Image Server configured with ArcGIS Server.
You can access an image service the same way you would any other service, by first connecting to the GIS server and then choosing the image service that is available.
Learn about connecting to GIS servers.