NAME

       r.null  - Manages NULL-values of given raster map.

KEYWORDS

       raster, null data

SYNOPSIS

       r.null
       r.null help
       r.null [-fincr] map=name  [setnull=val[-val][,val[-val],...]]   [null=float]   [--verbose]
       [--quiet]

   Flags:
       -f
           Only do the work if the map is floating-point

       -i
           Only do the work if the map is integer

       -n
           Only do the work if the map doesn't have a NULL-value bitmap file

       -c
           Create NULL-value bitmap file validating all data cells

       -r
           Remove NULL-value bitmap file

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       map=name
           Name of raster map for which to edit null file

       setnull=val[-val][,val[-val],...]
           List of cell values to be set to NULL

       null=float
           The value to replace the null value by

DESCRIPTION

       The function of r.null 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.

       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.

       The setnull 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.

       The null 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.

EXAMPLES

       Set specific values of a classified map to NULL:

       r.null map=landcover.30m setnull=21,22
        Set NULL-values of a map to a specific value:

       r.null map=fields null=99

NOTES

       Note that value is restricted to integer if the map is an integer map.

       r.null and reclassified maps:
       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).
       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:

       r.mapcalc newmap = reclass

SEE ALSO

       r.support and r.quant

AUTHOR

       U.S.Army Construction Engineering Research Laboratory

       Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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