An overview of metadata in ArcGIS Image Server
For many applications, metadata about imagery is as important as the image itself. For many of you, knowing the date of the acquisition of an image, is critical when making decisions based on information from the image. ArcGIS Image Server stores and distributes metadata about the image services and individual rasters that are used. There are many standards for such metadata. In ArcGIS Image Server, a set of metadata tags have been defined that are used for most applications.
Within ArcGIS Image Server there a two types of metadata that are stored and transmitted:
| • | Service metadata—This is general information about the image service. It is entered in the Image Service Editor using the Image Service Properties dialog box. The metadata is stored within the image service definition. When a user connects to the published service, some of the metadata fields are displayed to assist you in selecting the most appropriate service. Once a service is loaded, the Image Service Properties dialog box can be opened to display an extensive list of the image service metadata. |
| • | Raster metadata—This information about each raster can be assigned to the raster, such as the date and time it was captured or a categorization, such as quality and cloud cover. Raster metadata is originally stored in many forms and extracted into the raster process definition as one of the tasks when adding a raster type. The raster metadata for each input raster participating in an output image, is transmitted to the client application and can be viewed from within the Properties dialog box or exported to a file by the client. This metadata is then stored as Extensible Markup Language (XML) nodes within the raster process definition associated with the raster dataset. Such raster metadata can also be converted to raster attributes. Raster attributes are specifically identified metadata tags that should be extracted from the raster metadata and added to the source table of the image service. Using the Order by Attribute mosaic method, the display order of rasters can be controlled by the client. |
For more information on these types of metadata, see Creating metadata.
Details of metadata transmitted by the service provider to the client can be controlled from the Client Interface Control in the Image Service Properties dialog box that defines flags for transmit process metadata, raster footprints, raster info, and raster metadata. Process metadata is generated by the service provider and provides details of the processes applied to the raster and the parameters for processes. Raster footprints are XML structured Geography Markup Language (GML) that defines which part of the image comes from which raster. Currently, the interface does not make use of the footprint metadata. Raster info is data about rasters that are being read, such as size and location. Raster metadata is stored in a specified node within the raster process definition.
There are a large number of different metadata standards. Within ArcGIS Image Server, there has been an attempt to conform to both the Federal Geographic Data Committee (FGDC) and International Organization for Standardization (ISO) standards including some of the more common tags, but different users will have different requirements. Both service and raster metadata and can be customized. The customization can include the redefinition of the nodes as well as how they are displayed within the Image Service Editor and client properties interfaces.