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 oper-
       ate 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  available 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  pres-
       ence  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 counter-
       intuitive.   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)
