The human brain automatically interprets the vast amount of visual information available according to basic rules. Color, or hue, is used to categorize objects. Shading, or intensity, is interpreted as three-dimensional texturing. Finally, the degree of haziness, or saturation, is associated with distance or depth. This program allows data from up to three raster map layers to be combined into an image which retains the original information in terms of hue, intensity, and saturation.
Alternately, the user can run the program interactively by typing d.his without naming parameter values on the command line. In this case, the program will prompt the user for parameter values using the standard GRASS GUI interface.
While any raster map layer can be used to represent the hue information, map layers with a few very distinct colors work best. Only raster map layers representing continuously varying data like elevation, aspect, weights, intensities, or amounts can suitably be used to provide intensity and saturation information.
For example, a visually pleasing image can be made by using a watershed map for the hue factor, an aspect map for the intensity factor, and an elevation map for saturation. (The user may wish to leave out the elevation information for a first try.) Ideally, the resulting image should resemble the view from an aircraft looking at a terrain on a sunny day with a bit of haze in the valleys.
The brighten option does not truly represent a percentage, but calling it that makes the option easy to understand, and it sounds better than Normalized Scaling Factor.r.colors. Finally, the color is made somewhat gray-based on the red intensity of that cell in the saturation map layer. Again, this map layer should have a gray-scale color table associated with it.
H.i.s + G.(1-s) where H is the R,G,B color from the hue map i is the red value from the intensity map s is the red value from the saturation map G is 50% gray (R = G = B = 0.5)
Either (but not both) of the intensity or the saturation map layers may be omitted. This means that it is possible to produce output images that represent combinations of his, hi, or hs.
Users wishing to store the result in new raster map layers instead of displaying it on the monitor should use the command r.his.
g.region raster=elevation r.relief input=elevation output=elevation_shaded_relief d.mon wx0 d.his hue=elevation intensity=elevation_shaded_relief brighten=50
© 2003-2021 GRASS Development Team, GRASS GIS 7.8.6dev Reference Manual