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



NNAAMMEE
       rr..mmaasskk  - Establishes or removes the current working mask.
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..mmaasskk

DDEESSCCRRIIPPTTIIOONN
       The  _r_._m_a_s_k program allows the user to block out certain areas of a map
       from analysis, by "hiding" them from sight  of  other  GRASS  programs.
       This  is  done by establishing a mask.  While a mask exists, most GRASS
       programs will operate only on data falling inside the masked area,  and
       ignore any data falling outside of the mask.


       Because	the mask is actually only a reclass file called "MASK" that is
       created when the user identifies a mask using _r_._m_a_s_k, it can be copied,
       renamed,  removed,  and	used in analyses, just like other GRASS raster
       map layers.  The user should be aware that  a  mask  remains  in  place
       until  a  user renames it to something other than "MASK", or removes it
       using _r_._m_a_s_k or _g_._r_e_m_o_v_e.


       _r_._m_a_s_k provides the following options:
	     1 Remove the current mask
	     2 Identify a new mask
	    RETURN Exit from program
	The user establishes a new mask by choosing option (2).  The user will
       be  asked  to name an existing raster map layer from among those avail-
       able in the current mapset search path.	Once done, the user is shown a
       listing of this map's categories, and is asked to assign a value of "1"
       or "0" to each map category.  Areas assigned category  value  "1"  will
       become  part of the mask's surface, while areas assigned category value
       "0" will become "no data" areas in the MASK file.


       If a category is not assigned category value "1" it will  automatically
       be  assigned  the  category  value "0" in the resulting MASK file.  Any
       cells falling in category "0" will fall outside the newly formed  mask,
       and  their  presence will be ignored by GRASS programs run later on, as
       long as the MASK file remains in place.

NNOOTTEESS
       The above method for specifying a  "mask"  may  seem  counterintuitive.
       Areas  inside  the  mask are not hidden; areas outside the mask will be
       ignored until the MASK file is removed.


       This program actually creates a raster map layer (reclass type)	called
       _M_A_S_K,  which  can  be manipulated (renamed, removed, copied, etc.) like
       any other raster map layer.


       Somewhat similar program functions to those performed by _r_._m_a_s_k can  be
       done using _r_._m_a_p_c_a_l_c, _g_._r_e_g_i_o_n, and other programs.


       This program can only be run interactively.


       Note that some programs, like _r_._s_t_a_t_s, have options that allow the user
       to see the effects of the current mask  without	removing  the  current
       mask. See, for example, use of the --mm option for _r_._s_t_a_t_s.

SSEEEE AALLSSOO
       _g_._c_o_p_y

       _g_._r_e_g_i_o_n

       _g_._r_e_m_o_v_e

       _g_._r_e_n_a_m_e

       _r_._c_o_m_b_i_n_e

       _r_._i_n_f_e_r

       _r_._m_a_p_c_a_l_c

       _r_._r_e_c_l_a_s_s

       _r_._s_t_a_t_s

       _r_._w_e_i_g_h_t

AAUUTTHHOORR
       Michael Shapiro, 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.mask(1)
