About the ArcGIS Image Server process chain

One of the key features of the ArcGIS Image Server is its ability to process pixels between reading them from the raster source file and their transmission to a client application. The process chain is a list of actions that are to be performed on the raster data. This process chain is saved as part of the image service definition and raster process definition (.RPDef) file.

Learn about the raster process definition file

The following diagram is an example of a simple process chain used by ArcGIS Image Server:

In ArcGIS Image Server, there are two main parts to the complete process chain; the image service processes and the raster data processes.

Image service process chain

The image service process chain, also considered an output process chain, is applied to all raster data after the mosaicking process. It is defined in the image service definition (.ISDef) file. Generally, the service processes are used to render a mosaicked image for display. A typical use of a service process would be to convert a mosaic of elevation data into a shaded relief representation for display. Other typical examples can be computation of an NDVI and rendering results into different classes. When using rasters with high bit depth, the service process is often employed to convert the data to 8 bit for display. One restriction is that a service process cannot define the geometry of pixels. For example, a warp of the image cannot be applied as a service process. Warps including coordinate reprojection are applied as part of the raster process.

Raster data process chains

The raster dataset process chain is also considered an input process chain. This is defined by the raster process definition (.RPDef) file and is applied to each individual rasters prior to mosaicking. A single raster dataset can consist of multiple rasters. Therefore a process chain can be specified on each raster (band) within the raster dataset or on the group of rasters.

The georeferencing processes are applied on individual rasters. For example, a simple raster dataset can consist of orthorectified raster data with a pyramid of overviews, and each of the overviews can exist with different georeferencing. The raster process chain can be more complex; for example, a panchromatic raster can be converted to a color raster using the pansharpen process, which is applied depending on pixel size. Within an .RPDef file, there are separate sections for each raster, and each of these sections can contain a process chain.

Learn about applying raster processes

The raster group process chain is applied to all the rasters within a raster dataset. It is typically used to transform a raster into the required number of bands or pixel type required by the service. The raster group process is defined in the header or the .RPDef file.

Within the Image Service Editor interface (in ArcMap), these process chains can be viewed by selecting a raster dataset, clicking the Raster Properties button on the Image Service Definition Editor toolbar, then clicking the Process node to view the raster group processes, or by clicking the Raster node and clicking the Process tab to view the process chain for the individual rasters.

Learn about creating and editing process chains

When a request for an image covering a specified extent is received by ArcGIS Image Server, the service provider identifies the rasters that are required in the output image. For each of these rasters, the required pixels are read and passed through the raster process and raster group process. The individual processed rasters are then mosaicked together, and the resulting image is passed through the service processes before being sent back to the client.