Preparing image services

There are many things to consider when you are preparing to create an image service, because not all raster data is served in an equal manner depending on the capabilities you choose.

How many raster datasets are there?

If you have a single raster dataset that you want to serve, such as a mosaicked raster dataset in ArcSDE or a large digital elevation model (DEM), then ArcGIS Server can serve this directly. If, however, you need to serve a collection of raster datasets as a single image service, or you want to serve up many raster datasets that overlap completely and were captured at various dates or times as a single image service, you should create a mosaic dataset. You can then publish this to your server.

Can a raster catalog be served as an image service?

A raster catalog cannot be served directly. You need to create a mosaic dataset from the raster catalog or add it to a mosaic dataset and serve the mosaic dataset. You can create a mosaic dataset directly from the raster catalog using the Create Referenced Mosaic Dataset tool to serve it without building any overviews or editing any of the properties of the input raster dataset, . If you need to build overviews or edit the properties of the raster datasets, or even want to combine multiple raster catalogs within one mosaic dataset, then you need to create a new mosaic dataset using the Create Mosaic Dataset tool and add the raster catalog using the Add Rasters To Mosaic Dataset tool.

Is the raster data available for viewing as an image or as input for analysis?

The raster data is available for both viewing as an image and as input for analysis, depending on which capabilities you enable when you publish the service. If the users of the image service do not make adjustments to the appearance of the image, other than adjusting things like transparency, brightness, and contrast, and do not use the raster data as input for any analysis, then this data can be served with any of the capabilities. For the user to access the data in the image service to do further analysis, such as spatial analysis with the geoprocessing tools or generating a surface from elevation data, enable the additional WCS capability for the image service.

When working within ArcGIS, the Image Service capability provides the pixel information required to do analysis using the image service. However, if the user's application cannot connect to ArcGIS Server, then the WCS service is an ideal alternative.

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 the user to change the band combination or apply a stretch to the histogram to enhance the appearance of the image. If serving raster data using WMS, the user is not able 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 served 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, then 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?

When you serve a raster dataset or raster dataset layer, the raster dataset must be in its final state and ready for the user to use. However, when you publish a mosaic dataset, processing can be defined that is applied by the server on the fly, for example, orthorectification, enhancements, band combinations, band algebra, pan-sharpening, and filtering.