r.null(1)	       Grass User's Manual		r.null(1)



NNAAMMEE
       rr..nnuullll	-  The function of r.null is to explicitly create
       the NULL-value bitmap file.
       _(_G_R_A_S_S _5 _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..nnuullll

       rr..nnuullll	     --ffiinnccrr	    mmaapp==_n_a_m_e	     [sseettnnuullll==_v_a_l
       [_-_v_a_l][,_v_a_l[_-_v_a_l],...]]	[nnuullll==_v_a_l_u_e]

DDEESSCCRRIIPPTTIIOONN
       The  function  of _r_._n_u_l_l 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.

   FFllaaggss::
       _-_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 which  validates  all
	      data cells.

       _-_r     Remove NULL-value bitmap file.


   PPaarraammeetteerrss::
       mmaapp    raster map for which to edit null file

       sseettnnuullll==_r_a_n_g_e_[_,_r_a_n_g_e_._._._]
	      The values specified in the ranges are 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.

       nnuullll==_v_a_l_u_e
	      Eliminate the NULL value and replace it with value.
	      This argument is applied only to existing NULL val-
	      ues,  and  not  to the NULLs created by the setnull
	      argument.


NNOOTTEESS
       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

       Then he/she recodes this copy.

SSEEEE AALLSSOO
       _r_._s_u_p_p_o_r_t

       and

       _r_._q_u_a_n_t


AAUUTTHHOORR
       U.S.Army Construction Engineering Research Laboratory

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_4 _$



GRASS 5.0						r.null(1)
