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 not to 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:
- 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 - e.g. 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 JPG compressed, so this view requires the least bandwidth to deliver to the user), and/or
- Elevation Tinted Hillshade - (Hillshade with colormap applied)
- Slope Map (Slope with colormap applied)
- Aspect Map (Aspect with colormap applied)
NOTE: The sample scripts (and appropriate .rtf.xmls files) are available in the ArcGIS Image Management Workflows group on ArcGIS Online include examples of these alternative elevation products.
Note there are two methods of exposing such on-the-fly (OTF) processing as services: Using reference mosaic dataset & using server raster functions.
A reference mosaic dataset is a new mosaic dataset that references an existing mosaic dataset but can redefine some properties and also include additional functions such as Hillshade. Such reference 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 that each published reference 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 application such as ArcGIS for Desktop 10.1 and web applications based on the ArcGIS WebAPIs. 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, readers may follow this link for help on referenced mosaic datasets, and this link for discussion of raster functions.