About the raster process definition

In ArcGIS Image Server, the raster process definition (.RPDef) file defines a raster dataset that is used in the image service definition. Often raster datasets consist of georeferenced or orthorectified imagery, and ArcGIS Image Server only has to mosaic each of these together to create an image service for the client application. However, you may need to define specific georeferencing for a raster, such as orthorectification, or something more complex that may also include enhancements, classification, or panchromatic sharpening.

When the raster dataset is added to an image service definition, a raster process definition is created to fully encapsulate the definition of the raster dataset. The only information about a raster dataset that is not included in the .RPDef file is the actual pixel values, which are large in volume. Instead, these are explicitly referenced. Internally, in the image server, whenever a raster dataset is used to create a requested image, the service provider obtains all details on how to access and process the pixels using the properties defined in the .RPDef file. Metadata about the raster dataset that is sent to the client application is also included in the .RPDef file.

A raster dataset is added to the image service definition by using the Add Raster Dataset operation and identifying the raster type to add. According to the selected raster type, different sources and parameters required to define the raster datasets are then prompted for, and an .RPDef is created for each raster dataset and added as a record in the service table. The service table defines key attributes of the raster dataset and a pointer to the .RPDef, which defines the raster dataset and includes pointers to the actual pixels.

Typically, a raster process definition file contains the following:

• Footprint—The footprint of the data pixels. When an .RPDef file is included in an image service definition, the footprint is transformed to the spatial reference system of the image service and extracted to the image service definition footprint shapefile.
• Spatial reference—Spatial reference system of the raster dataset.
• Number of bands—Number of bands in the raster dataset.
• Pixel type—Numeric type of pixel value, for example, 8-bit integer or 32-bit float.
• Bit depth—Out of the number of bits available, those that contain actual values.
• Seamline—The seamline polygon to be used when a seamline mosaic is created. Often, this is not available when a raster dataset is added but could be defined for advanced applications.
• High and low pixel size range—These define the range of pixel values that exist in the raster dataset. For example, in a simple orthorectified image, both the high and low values can be the same, corresponding to the resolution of the imagery. Datasets that include pyramids or multiple overlapping rasters can have a range of pixel sizes. When an .RPDef file is included in an image service definition, these values are included in the LoPS and HiPS columns in the service table.
• Histogram statistics—The histogram and histogram statistics for the raster dataset. There can be multiple histograms representing both the unprocessed rasters and raster output from raster processes.
• Metadata—Data providing information about the raster. This data is extracted from the source, depending on the raster type. For generic raster types, such as GeoTIFF, the amount of metadata available can be limited. For more specific raster types, such as QuickBird, the metadata can include a number of different attributes, such as date and time of acquisition.
• Raster group process—Definition of the raster dataset process chain to be applied to all rasters within the raster dataset.
• Multiple raster items—A raster process definition contains the definition of one or more rasters. Each has a definition—raster processes as well as information—about the format; the location of the pixels; and metadata, such as histogram statistics.

Properties of a raster process definition

You can set the properties of a raster process definition for selected raster datasets using the Raster Properties dialog box.

These properties are organized into five groups:

• Info—Contains general information about the raster process definition, such as a version, the author's name, the type of .RPDef generator, creation date, and creation time.
• General—Contains the general raster properties, such as the pixel size range, bit depth, whether transparency is allowed, unit of measure, and histogram statistics.
• Metadata—Contains information about the raster that the client can view as metadata.
• Raster Group Process—Defines the chain of processes to be applied to the raster dataset. These processes are applied to all rasters before the mosaicking operation.
• Rasters—Lists one or more rasters. For each, the general properties, such as the ID and pixel sizes as well as the raster process to be applied to the pixels and the format information about the raster, are defined.