Using the Hill Shade tool, you can obtain hypothetical illumination of a surface by determining the illumination values for each cell in a raster grid file. Hill shading darkens areas that are sloped, or darkens areas that are obscured by higher elevated areas. This tool works on the premise of brightening areas that face the sun directly. Hill shading can significantly enhance the visualization of a surface for analysis or graphical display, especially when using transparency.
Once sun shading is a part of your map, you can use it with:
- a DEM to create an elevation or relief effect.
- a contour map and create a real world topographic data.
- an aerial image and create custom texture and perspective to the imagery.
The source sun position used for shading and highlighting are independent, however you cannot enable sun highlight without enabling sun shading.
The primary factor when creating a hillshade map for any particular location is the location of the sun in the sky.
Sun Shadow
Sun shading helps you calculate the amount of sun or shade for a 3D surface or a 2D gridded surface. As mentioned above, a sun shade specifies the brightness or darkness for each cell on a raster grid. This depends on how a cell is positioned with respect to a light source, for example, the sun. The two variables that define the light source are elevation and azimuth. Elevation ranges from 0-90 degrees and it defines the angle of the light source from the horizon. 0 degrees means that the light source is on the horizon. 90 degrees means that the light source is directly overhead.
Azimuth ranges from 0-360 degrees. The azimuth angle is the compass direction from which the sunlight is coming from. In the Northern compass direction, the azimuth angle is 0 degree, and in the North Western compass direction, the azimuth angle is 315 degrees.
The example raster below has an elevation of 45 degrees and an azimuth of 315 degrees.
Highlight
Sun highlighting helps you control how bright areas on the map display. Using highlighting, you can make areas brighter than the non-sun shaded grid file. Highlighting also depends on the elevation and azimuth.
The example raster below shows the same grid with highlighting.