There are many things to consider when you're preparing to create an image service, because not all raster data is served in an equal manner, depending on the capabilities, and the operations within them, you choose.
Is there one raster dataset or many raster datasets?
With ArcGIS Server, you can publish single raster datasets, such as a mosaicked raster dataset or a large DEM. If you need to share many raster datasets that compose a single image service, or you want to share many raster datasets that overlap completely and were captured at various dates or times and that compose a single image service, you should create and publish a mosaic dataset.
A raster catalog cannot be published. However, you can convert the raster catalog to a mosaic dataset and publish the mosaic dataset using one of the following options:
- Create a new mosaic dataset using the Create Mosaic Dataset tool and add the raster catalog using the Add Rasters To Mosaic Dataset tool.
- This option will allow you to modify the mosaic dataset and its components, including adding additional raster data.
- Create a mosaic dataset from the raster catalog using the Create Referenced Mosaic Dataset tool.
- You cannot build any overviews, update the boundary, or edit any of the properties of the input raster datasets (including footprints).
Is the raster data for viewing as an image or as input for analysis?
Overall, when working within ArcGIS, the Image Service capability provides the information required to do analysis using the image service. However, if your application cannot connect to ArcGIS Server, then the WCS service is an ideal alternative.
As an image
The user will not make adjustments to the appearance of the image, other than adjusting things such as transparency, brightness, and contrast.
Used in analysis
The image service will be used as data to do analysis, such as spatial analysis, with the geoprocessing tools or generating a surface from elevation data.
The user will be taking measurements from the image service using mensuration tools, such as those that measure height.
Does the data have multiple bands or need to be enhanced?
The layer properties of an image service with Image Service or WCS capabilities allow users to change the band combination or apply a stretch to the histogram to enhance the appearance of the image. If publishing raster data using WMS, the user is unable to change the rendering or the band combination; therefore, a raster dataset layer, mosaic dataset, or mosaic dataset layer are the preferred inputs for a WMS service so the display properties can be set correctly. If a raster dataset is published using the WMS capabilities, the default raster display settings are applied. If a mosaic dataset is used, and the source images contain more than three bands, the mosaic dataset needs to have its number of bands defined, so it serves either a three-band color (RGB) or one-band grayscale image service.
Is any processing required on the image service data?
When you publish an image service, you can define processing (using functions) that is applied by the server on the fly, for example, orthorectification, hillshading, enhancements, band combinations, band algebra, pan sharpening, and filtering. Basic functions are supported on image services (via REST and SOAP), such as Aspect, Colormap, NDVI, Slope, Hillshade, and Stretch. You can also create a raster function template file (.rft.xml) to use any of the raster functions and to chain them together. To learn more, see Server-side processing with raster functions.
Will users be measuring height from the image service?
If users will be using the mensuration tools, there are some settings on the image service to allow this. As in ArcMap, the mensuration capabilities are limited by the data, but also by the presence of a DEM. If your users will be getting measurements in 3D, you can provide a DEM with the image service that will be used. This setting is in the service properties.
Will users be downloading imagery from the image service?
If you're publishing a mosaic dataset as an image service, users can connect to it and download the source files as they would if they were using the mosaic dataset directly. By default, this is already enabled on the mosaic dataset. If you want to change the limit, you need to set the Maximum number of items downloadable per request property on the mosaic dataset (you can reduce this value when publishing the image service but not increase it). If you want to disable this function, set the value to 0. When publishing, you need to enable the Download operation, which is part of the Imaging capability of the image service.
You also need to manage the directories involved. By default, the server will move the source images to its output directory before transmitting to the user. This adds an additional load to the server to move these files. Alternatively, you can associate a virtual directory with the server's output directly so the source files are not moved. The only risk with this virtual directory is that all the source files in this directory are directly exposed though HTTP. You also need to configure the MIME types for the virtual directories.
When using download on an image service, it is always recommended that you secure the server.
Will users be uploading imagery to the image service?
You can publish a mosaic dataset as an image service and allow users to upload their own data into it and edit the properties associated with what they've uploaded. To enable this, you must enable the Editing operation within the Imaging capability when publishing the mosaic dataset.
To use this functionality, a geodatabase must be registered with the server, because your mosaic dataset must reside in a geodatabase. You can publish the image service with Editing by one of the following:
- Sharing the geodatabase with ArcGIS Server and publishing the mosaic dataset from the shared geodatabase.
- Ensuring a geodatabase is registered as a replicated database with ArcGIS Server. Make sure the same mosaic dataset is stored in the enterprise or file geodatabase, and then publish the mosaic dataset from your file geodatabase.
- Ensuring a geodatabase is registered as a shared database with ArcGIS Server, and publishing a mosaic dataset from within a file geodatabase. This will copy the mosaic dataset from the file geodatabase to the enterprise geodatabase.
Since the mosaic dataset will be in an enterprise geodatabase, make sure it is set up to consume the allowed raster types by using the Alter Mosaic Dataset Schema tool. When the mosaic dataset is published, there is a schema lock; therefore, you will have to stop the image service to alter the schema if it was not altered prior to publishing.
You can also set up editor tracking on your mosaic dataset whereby ArcGIS can record the following information for each item added or edited:
- Name of the user who created it
- Date and time it was created
- Name of the user who edited it
- Date and time it was last edited
The fields to contain this information can be designated on the Editor Tracking tab on the Mosaic Dataset Properties dialog box, or they can be defined or created using the Enable Editor Tracking tool.
When publishing, make sure to configure the Editing parameters, including defining the directory on the server where the user's imagery will be uploaded (if users can add, update, or delete items in the image service), and define the raster types that a user can choose when adding their data to the image service.
Is access speed critical?
Image services can be cached to improve the access speed for the user to the imagery. An image service cache is not dynamic; it must be pre-generated. An image service cache can only support a one- or three-band image. This is ideal for most orthophotography but not image services with more than three bands of data. When publishing a four-band (or greater) image service, the first three bands will be cached to create a color image; however, if the client chooses to change the band combination, they will no longer be using the cache, and the image service will dynamically return the required image.
When using ArcGIS Desktop applications, such as ArcMap, you can access the cached image service or access it as a dynamic image service. You can control how it's being accessed by checking or unchecking Enable Cache View Mode in the context menu on the image service layer in the table of contents.