The r.rescale.eq program rescales the range of category values appearing in a raster map layer with equalized histogram. A new raster map layer, and an appropriate category file and color table based upon the original raster map layer, are generated with category labels that reflect the original category values that produced each category. This command is useful for producing representations with a reduced number of categories from a raster map layer with a large range of category values (e.g., elevation). Rescaled map layers are appropriate for use in such GRASS programs as r.stats,, and r.coin.


To rescale an elevation raster map layer with category values ranging from 1090 meters to 1800 meters into the range 0-255, the following command line could be used (without the from parameter, the full value range will be used):
r.rescale.eq input=elevation from=1090,1800 output=elevation.255 to=0,255


Category values that fall beyond the input range will become NULL. This allows the user to select a subset of the full category value range for rescaling if desired. This also means that the user should know the category value range for the input raster map layer. The user can request the r.rescale.eq program to determine this range, or can obtain it using the r.describe or command. If the category value range is determined using r.rescale.eq, the input raster map layer is examined, and the minimum and maximum non-NULL category values are selected as the input range.


r.coin, r.describe,, r.mapcalc, r.reclass, r.rescale,, r.resample, r.stats


Michael Shapiro, U.S.Army Construction Engineering Research Laboratory

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