Raster functions are operations that apply processing directly to the pixels of imagery and raster datasets, as opposed to geoprocessing tools, which write out a new raster to disk. Calculations are applied to the pixels of the original data as the raster is displayed, so only pixels that are visible on your screen are processed. As you zoom and pan around, the calculations are performed on the fly. Since no intermediate datasets are created, processes can be applied quickly, as opposed to the time it would take to create a processed file on disk.
There are many of out-of-the-box functions that are provided in the software that can be used for radiometric correction, geometric correction, data management, visualization, and analysis. The Raster Functions pane can be accessed through the Imagery tab or the Analysis tab. Functions can be applied individually or combined to create function chains. There are several methods for applying functions depending on the structure of the dataset.
The following three types of functions are available in AllSource:
- Local Functions—A collection of ready-to-use raster analysis and management tools that are available in the Raster Functions pane.
- Global Functions—Global functions provide you with the ability to perform processing at a specific resolution and extent. By default, global functions process rasters at the source resolution and full extent as opposed to regular functions, which are applied to pixels that are visible on your screen.
- Custom Functions—Custom functions can be written in Python and applied in the same way as out-of-the-box-functions.
Functions can be applied to the following data types:
- Raster layers—Functions can be applied to raster layers using the Raster Functions pane.
- Mosaic datasets—Functions can be applied to the entire mosaic dataset. To apply a raster function to a mosaic dataset, right-click the mosaic dataset in the Catalog pane and click Edit Mosaic Dataset Functions. When applying a function to a mosaic dataset, the function remains applied to the mosaic dataset during distribution, such as when sharing and publishing.
- Rasters items in a mosaic dataset—Functions can be applied to individual items in a mosaic dataset using the Edit Raster Function tool. When applying a function to a mosaic dataset, the function remains applied to the mosaic dataset during distribution it, such as when sharing and publishing.
- Image service layers—Raster functions can be applied to image services using the Raster Functions pane. You can also add individual items from image services and apply functions to them. This can be done by expanding the image service in the Catalog pane and adding the items to your map.
- Raster analysis with Portal for ArcGIS—Portal for ArcGIS has been enhanced to perform distributed server-based processing on imagery and raster data. This technology enables you to boost the performance of raster processing by processing data in a distributed fashion, even at full resolution and full extent. You can use the processing capabilities to define the processing to be applied to raster data and perform processing in a distributed fashion using your on premises portal. The results of this processing can be accessed in the form of a web imagery layer that is hosted in their ArcGIS organization.
Raster function templates
Functions can be combined into function chains which can be saved as raster function templates using the Function Editor. Raster function templates can be used and distributed in several ways:
- Raster layers—Processing templates can be applied to layers in a project in the same way as an out-of-the box function. Processing templates are located in the Raster Functions pane on the Custom and Project tabs.
- Mosaic dataset or image service processing templates—Processing templates can be added to mosaic datasets and published as an image service. Adding processing templates to a mosaic dataset can be performed by right-clicking the template in the Catalog pane and clicking Manage Processing Templates. The Manage Processing Templates pane can be used to add, edit, and organize templates associated with mosaic datasets. When publishing a mosaic dataset as an image service, the associated processing templates are published with the service. Once the template is added to the mosaic dataset or image service, the processing templates can be accessed through the Processing Templates drop-down menu on the Data tab when the layer is selected in the Contents pane. They can also be accessed through the layer Properties on the image layer in the Contents pane.
- Share to Portal—Processing templates can be shared to a portal by right-clicking the template in the Raster Functions pane and clicking Share to Portal. You must be connected to an active portal for this option to be available. Once shared, portal users can download them or apply them to rasters directly.
- Export—Templates can be exported to disk as rft.xml files from the Raster Functions pane. They can then be shared with other users. These files can be imported in several places across the ArcGIS platform.