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- <h2>DESCRIPTION</h2>
- The function of <em>r.null</em> is to explicitly create the NULL-value
- bitmap file. The intended usage is to fix "old" maps that don't have a
- NULL-value bitmap file (i.e. to indicate if zero is valid value or is to be
- converted to NULL). The module does not work with reclassified maps.
- <p>
- The design is flexible. Ranges of values can be set to NULL and/or the NULL
- value can be eliminated and replace with a specified value.
- <p>
- The <b>setnull</b> parameter is used to specify values in the ranges to
- be set to NULL. A range is either a single value (e.g., 5.3), or a pair of
- values (e.g., 4.76-34.56). Existing NULL-values are left NULL, unless the
- null argument is requested.
- <p>
- The <b>null</b> parameter eliminates the NULL value and replaces it with
- value. This argument is applied only to existing NULL values, and not to the
- NULLs created by the setnull argument.
- <h2>EXAMPLES</h2>
- Set specific values of a classified map to NULL:<br>
- <div class="code"><pre>
- r.null map=landcover.30m setnull=21,22
- </pre></div>
- Set NULL-values of a map to a specific value:<br>
- <div class="code"><pre>
- r.null map=fields null=99
- </pre></div>
- <h2>NOTES</h2>
- Note that value is restricted to integer if the map is an integer map.
- <p><em>r.null</em> and reclassified maps:<br>
- The problem is, if r.null was run on the reclass raster it would alter the
- original and any other reclass rasters of the original. Therefore r.null
- doesn't allow to recode reclassified maps (products of r.reclass).
- <br>
- So, the way to recode such a map is: The user makes a raster out of the
- reclass that isn't a reclass by copying it:<br>
- <div class="code"><pre>
- r.mapcalc newmap = reclass
- </pre></div>
- <h2>SEE ALSO</h2>
- <em><a href="r.support.html">r.support</a></em>
- and
- <em><a href="r.quant.html">r.quant</a></em>
- <h2>AUTHOR</h2>
- U.S.Army Construction Engineering Research Laboratory
- <p><i>Last changed: $Date$</i>
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