Image services
Image services |
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| Release 9.3 |
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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 layer file referencing a raster dataset, or a compiled image service definition (containing one or more raster datasets and defined processes) created using ArcGIS Image Server. Once you publish this raster data to your server, you can use the resulting image service in ArcGIS Desktop the same way you would add any other GIS service layer.
Important: If you plan on creating image services based on compiled image service definitions, you must register ArcGIS Image Server with ArcGIS Server.
Learn more about registering ArcGIS Image Server with ArcGIS Server.
When you publish an image service, you can choose to enable it with Open Geospatial Consortium Web Map Service (WMS) or Web Coverage Service (WCS) capabilities. The raster data source that you use to publish your service determines the capabilities and layer properties that are available to you. A default capability of imaging is always enabled.
An image service served with the imaging capability 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 or layer and any 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 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. For this they will need the IP address or computer name and port information for the server.
An image service served with the WMS capability has the same functionality of any other WMS service. You do not have to create a map document containing a raster dataset layer. An image service served as a WMS service contains only one layer, since it is representing only one input. You can connect to a WMS service in ArcGIS Desktop, through Web Mapping Applications, or using other applications that support 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 cannot change any of the properties of the data delivered via the WMS service. Because the rendering is defined by the layer file or the compiled image service definition, only image services published with these sources have the WMS capability available. In other words, you cannot enable the WMS capability if you are publishing the image service directly from a raster dataset.
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), single-band with a colormap, or 3-band combination. Additionally, the data will be resampled to an 8-bit image.
Publishing the image service with the WMS capability is the way that you can use the service in ArcGIS Explorer or ArcGIS Server Web Mapping Applications, since both of these support WMS as a data source.
You can enable the WCS capability on any type of image service, regardless of the raster data source type. You can connect to a WCS service via ArcGIS Desktop or third-party applications that support 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. 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.
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.
If you have a single raster dataset that you want to serve, such as a mosaicked raster dataset in ArcSDE or a large digital elevation model (DEM), then ArcGIS Server can serve this directly. If, however, 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 should use the ArcGIS Image Server extension. Use the Image Service Definition Editor toolbar in ArcMap (provided with the extension) to create a compiled image service definition. You can then publish this to your server.
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.
The raster data is available for both viewing as an image and as input for analysis, depending on which capabilities you enable when you publish the service. 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 you should enable the WCS capability for the image service.
The layer properties of a non-WMS image service allow you 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 you cannot change the rendering or the band combination, therefore, only a raster dataset layer and image service definition are valid inputs for a WMS service. If an image service definition is used, the output properties need to be defined as 3-band color (RGB) or 1-band grayscale.
When you serve a raster dataset or layer file referencing a raster dataset, it must be in its final state and ready for the user to use. However, when you publish a compiled image service definition, the server performs on-the-fly processing such as orthorectification, enhancements, band combinations, band algebra, pan sharpening, and filtering.
Your options for publishing image services will vary depending on which software you have:
I have ArcGIS Server and the ArcGIS Image Server extension
You can publish raster datasets, layer files that reference raster datasets, and compiled image service definitions. You can use either ArcCatalog or Manager to publish the service. Follow the steps in Publishing a GIS resource to the server. When prompted for the resource, browse to the raster dataset, layer file, or compiled image service definition that you want to publish.
I have ArcGIS Server only
You can only publish raster datasets and layer files that reference raster datasets. You can use either ArcCatalog or Manager to publish the service. Follow the steps in Publishing a GIS resource to the server. When prompted for the resource, browse to the raster dataset or layer file that you want to publish.
I have ArcGIS Image Server only
You can only publish compiled image service definitions. You cannot enable the WMS or WCS capabilities, and limited imaging capabilities will be available. Users can only connect to ArcGIS Image Server with a direct connection using the clients provided with the extension.
You can access an image service the same way you would any other service by first connecting to the GIS Server, then choosing the image service that is available.
Learn about adding an image service layer to ArcMapThe image service layer has properties, similarly to any other layer in ArcGIS. Like a raster dataset layer, the Image Service Layer Properties dialog box contains the General, Source, Extent, Display, and Symbology tabs. The General, Source, Extent, and Display tabs are similar to the raster dataset layer and other layers; however, the Display tab has an additional option to control the compression of the transmitted image service. This transmission compression can be preset in an image service definition; however, the user will always have the ability to change this. A highly compressed image will be transmitted faster than an uncompressed image, but the image quality may not be as good. The Symbology tab is similar to the raster dataset layer; however, the user will only have the option to change the renderer using the RGB or Stretched renderers. Here the user can change the renderer, change the stretch applied to the histogram, and alter the background color and NoData representation.
When the image service is created from an image service definition, additional layer properties are presented on two additional tabs--the Mosaic tab and the Metadata tab. The Mosaic tab allows the user to change the mosaic method, such as By Attribute or Closest to Center; choose a field that will contain values used to sort on when using the By Attribute mosaic method; and specify the value by which the imagery will be ordered. The Metadata tab provides information about the image service, the returned image, any processes that were applied, and specifics about the source datasets. This information will be available for any image service that is derived from an image service definition, whether it is served from ArcGIS Server or the ArcGIS Image Server stand-alone configuration.
For a detailed example of preparing, publishing, and using an image service, see Tutorial: Publishing an image service.