Raster Functions: Accessing and Applying for Elevation

A raster is a geographic dataset that consists of pixels which are organized in rows and columns. Each pixel has a value, such as elevation. Each pixel also has an x and y coordinate which gives it a location.

A raster function is a defined processing operation that can be applied to a raster. The on-the-fly application does not change the underlying raster data, just how it is displayed. On CT ECO, raster functions are available for image services of DEMs (digital elevation models, or pixel based bare earth elevation).

Elevation Services on CT ECO with Raster Functions

They are evident by the year at the end. The aspect, elevation, hillshade, shaded relief and slope are based on the 2016 DEMs and already have a function applied.

Statewide 2016 More info REST
Central 2014 More info REST
Coast 2012 More info REST
East 2010 More info REST
Northwest 2011 More info REST
Southeast 2011 More info REST
Southwest 2011 More info REST

Hillshade Services on CT ECO with Raster Functions

Hillshade is a way to look at topography by adding an illumination source. Just as the sun moves across the sky, the illumination source can be set to any azimuth, or angular direction like a circle where 0 is North, 90 is east, 180 is south and 270 is west. Different features are visible on the hillshade depending on the illumination angle which is why multiple hillshade functions are included for user application in ArcGIS Online and Desktop GIS. All functions have an altitude of 45 and a Z factor of 2. If you need a different angle and do not have desktop GIS, please email us (information in the footer). These raster functions are available with the Elevation service and the Hillshade SE service.

Hillshade default 315
Hillshade NW 315 315 (same as default)
Hillshade E 90 90
Hillshade NE 45 45
Hillshade SE 135 135

Apply a Raster Function in ArcMap

Go to arcgis.com, log in and add an elevation service from CT ECO. Detailed instructions here if you need them. Remember to add one of the services that has functions.

  • Click the three blue dots to open the menu then choose Image Display (right).
  • Choose the renderer, or function from the dropdown list (left). Optionally, choose a stretch. Click Apply. The elevation is now shown with the function applied. Note that the same service can be added multiple times with different renderers applied.

Raster Functions

Aspect can be thought of as slope direction. The values of the aspect layer are the compass direction of the slope with north being 0, east being 90, south being 180 and west being 270.

Hillshade is a grayscale model of terrain with the sun's angle taken into account for shading the terrain. Hillshade varies by illumination angle so multiple hillshade functions are available.

Shaded Relief is a color representation of the terrain that takes the sun's angle into account.

Slope represents the rate of change of elevation. The output is shown in degrees from 0 to 90.