Referenced mosaic datasets

In addition to accessing the elevation values, users typically desire many additional representations of elevation data (listed below). It is generally recommended to not preprocess the data to create static representations of these different products, but use the power of the mosaic dataset to perform on-the-fly processing.

Recommended services based on elevation data that may be generated on the fly (using raster functions) to provide quantitative values include the following:

• Slope—Slope of the terrain, in degrees or percent rise.
• Aspect—Orientation of the terrain, from 0 to 360 degrees.
• Ellipsoidal Height—Calculated by adding the elevation derived mosaic dataset to an appropriate geoid, for example, EGM2008, to shift elevation values to ellipsoidal height. This is useful for orthorectification of satellite imagery.

For common visualizations, these additional services are recommended:

• Hillshade—Single-band grayscale, which may be JPEG compressed, so this view requires the least bandwidth to deliver to the user.
• Elevation Tinted Hillshade—Hillshade with color map applied.
• Slope Map—Slope with color map applied.
• Aspect Map—Aspect with color map applied.

NOTE: The sample scripts (and appropriate .rtf.xml files) are available in the ArcGIS Image Management Workflows group on ArcGIS Online and include examples of these alternative elevation products.

Note that there are two methods of exposing such on-the-fly (OTF) processing as services: using referenced mosaic datasets and using server raster functions.

A referenced mosaic dataset is a new mosaic dataset that references an existing mosaic dataset but can redefine some properties and also includes additional functions such as Hillshade. Such referenced mosaic datasets, when published, have their own service endpoint. Such services, when added to an application directly, display the required functions and can therefore be served also as WMS and WCS. The disadvantage of this approach is that each published referenced mosaic dataset will take up some resources on the server.

When a mosaic dataset is published, server raster functions can be defined (as .rft.xml files). These functions are applied on demand and become accessible as selectable functions to applications such as ArcGIS 10.1 for Desktop and web applications based on the ArcGIS Web APIs. The advantage is that they do not take up additional server resources and can be easily extended with more functions without needing to host additional image services.

For more background information, see this link for help on referenced mosaic datasets, and this link for discussion of raster functions.