Understanding how to create a new image service definition

Legacy:

ArcGIS 10 is the last release of the stand-alone ArcGIS Image Server product. The image service definition (.ISDef) has been replaced by an improved geodatabase data model—the mosaic dataset—which can be published as an image service using the ArcGIS Server Image extension.

The Service Editor component is used within ArcMap via the Image Service Definition Editor toolbar. This component is used to create and edit the image service definitions. An image service definition is made up of several files and folders. The key attributes of an image service definition are contained in an Extensible Markup Language (XML) file, ImageService.ISDef. To learn about the files that make up an image service definition, see The image service definition file structure or About the image service definition file.

There are two options for creating an image service definition; the one you use depends on how advanced the image service definition will be. The Image Service Editor Wizard allows you to create three of the most common types of image service definitions: panchromatic, color, or elevation. A panchromatic image service definition is any single-band image service, such as 1-bit scanned maps or grayscale aerial photography. A color image service definition is a combination of three bands (red, green, and blue) that creates a color image, such as a color orthophoto, Landsat or QuickBird band combination, or an internal color map within data you are using. An elevation image service definition can be used to create a hillshaded digital elevation model (DEM) or a slope product from a DEM, or it can be used to create an elevation image service to orthorectify the data of another image service.

The Image Service Editor Wizard walks you through all the steps required to create an image service definition, including adding the data, optimizing the image service definition, enhancing the imagery or visualizing the elevation data, and compiling the service.

If you need to build more advanced image service definitions that may, for example, use a variety of processes, choose New Service Definition from the Advanced menu. This displays the Image Service Definition dialog box where you enter the required information to start creating an image service definition. This information is used to generate the image service definition, which is displayed in ArcMap as a group layer in the table of contents (as shown below). You can then add raster datasets, define the processes, and set other properties of the image service definition.

The footprint is the first layer that is contained in the image service definition group layer using the advanced methods. When using the New Image Service Wizard, the footprint is also built; however, the wizard walks you through all the following steps that you would otherwise have to do independently, thus resulting in a complete group layer. The footprint contains the outline of the valid pixel data in each raster dataset, in the spatial reference system of the raster dataset, after the data is added. The example below displays a raw Landsat scene and the footprint that is derived. In this case, the extent of the valid pixel data is not rectangular as suggested by the file extents. The valid pixel data is actually contained within a skewed rectangle in the dataset, and the other pixel values surrounding this skewed rectangle are null data.

There are many cases where the footprint will be the extent of the file, thus resulting in rectangular footprints. You can edit the shape of the footprint. For example, you may want to exclude areas you do not want to display, such as areas of cloud cover in an image or a legend in a scanned map.

The contents of the image service definition you create are contained in a folder with the name you give the image service definition and an .ISDef extension, such as Landsat321.ISDef. This folder contains the image service definition XML, footprint, seamline, boundary information, and raster process definition files. To move or copy the image service definition contents to another location, simply move or copy the image service definition folder (with its contents). The paths stored within the image service definition are relative to the folder contents.

The workflow to create an image service definition

The stages in the workflow of creating an image service definition using the advanced commands are as follows:

1. Create a new image service definition, thus creating an image service definition file (.ISDef).
2. Edit the image service definition properties. You can do this at any time before compiling the image service definition.
3. Add raster datasets to the image service definition.
4. Build the image service definition. You need to build the image service definition to preview, optimize, or compile the image service definition. During the build stage, you are deriving and validating service parameters such as pixel size ranges and boundaries, computing derived images, validating tiles, and extracting metadata.
5. Optimize the image service definition. This is optional; however, it is highly recommended. Optimization options include generating service overviews, derived rasters, and derived tiles.
6. Compile the image service definition, thus creating a compiled image service definition (.ISCDef).

The New Image Service Wizard follows this same workflow.

The Image Service Definition dialog box parameters

Parameters on the Image Service Definition dialog box define the key aspects of the image service and should not be changed once defined. These parameters specify the location of the image service definition and control how the internal mosaicking of the raster data is performed.

Image Service Definition dialog box parameters

Parameter	Description
Service definition	Type the name and location where the image service definition folder is created. The system provides a default name and location that you can change. This is also the default name of the image service a client uses to access the image service. The default name of the image service can be specified on the Image Service Definition Properties dialog box.
Spatial reference	Choose the spatial reference system to be used for all internal searches and derived tiles. The spatial reference system should be selected such that no coordinate system boundaries exist within the extents of the required image service definition. For example, it would be advantageous to specify the Mercator projection while using data that covers multiple Universal Transverse Mercator (UTM) zones rather than specifying a single UTM zone. Once the spatial reference is defined, it cannot be easily changed.
Service type	Specify the type of image service to be created. All input rasters are converted to this type of raster for mosaicking internally prior to applying a service process. After defining the service type, it should not be changed. The type of output can be changed later using a service process. There are four service types—color (RGB), panchromatic, 4 band (RGBI), and elevation—that have the default number of bands and pixel type defined. The custom service type allows you to define the key parameters based on your requirements.
Number of bands	Specify the number of bands that will be mosaicked together to form the output of the image service definition. All rasters that are mosaicked together in an image service must have the specified number of bands. Rasters with a different number of bands must be converted to a raster with the specified number of bands using raster processes. The output of the image service can have a different number of bands; for example, an image service definition with grayscale imagery can be created from color imagery.
Pixel type	Specify the pixel type of rasters that will be mosaicked to form the output of the image service definition. Rasters that are mosaicked must have this pixel type, but the output service can be different. For standard color imagery, you can choose unsigned 8-bit integer.
Bit depth	Specify the number of bits of the mosaicked image. For example, a 16-bit-depth raster may use only 12 bits compared to the available 16 bits. This value affects the histogram and radiometric transformations used.
Color space	Define the relationship between the bands for each pixel. This is required primarily to activate compression.

Image Service Definition dialog box parameters