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 argu-
	      ment is applied only to existing NULL values,  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)
