r.surf.idw2(1)		      Grass User's Manual		r.surf.idw2(1)



NNAAMMEE
       rr..ssuurrff..iiddww22  - Surface generation program.
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ssuurrff..iiddww22 iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e [nnppooiinnttss==_c_o_u_n_t]

DDEESSCCRRIIPPTTIIOONN
       _r_._s_u_r_f_._i_d_w_2  fills  a  raster matrix with interpolated values generated
       from a set of irregularly spaced data points using numerical approxima-
       tion (weighted averaging) techniques.  The interpolated value of a cell
       is determined by values of nearby data points and the distance  of  the
       cell from those input points.  In comparison with other methods, numer-
       ical approximation allows representation of more complex surfaces (par-
       ticularly  those with anomalous features), restricts the spatial influ-
       ence of any errors, and generates the  interpolated  surface  from  the
       data  points.   It is the most appropriate method to apply to most spa-
       tial data.


       The program will be run non-interactively if  the  user	specifies  the
       values  of needed program parameters and any desired optional parameter
       values on the command line, using the form: rr..ssuurrff..iiddww22 iinnppuutt==_n_a_m_e oouutt--
       ppuutt==_n_a_m_e [nnppooiinnttss==_c_o_u_n_t]



       Alternately,  the user can simply type rr..ssuurrff..iiddww22 on the command line,
       without program arguments.  In this case, the user will be prompted for
       parameter  values  using the standard GRASS user interface described in
       the manual entry for _p_a_r_s_e_r.

   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      Name of an input raster map layer that contains a set of irregu-
	      larly  spaced  data  values; i.e., some cells contain known data
	      values while the rest contain zero (0).

       oouuttppuutt==_n_a_m_e
	      Name to be assigned to the new output raster map layer  contain-
	      ing a smooth surface generated from the known data values in the
	      input map layer.

       nnppooiinnttss==_c_o_u_n_t
	      The number of points to use for interpolation.  The  default  is
	      to  use the 12 nearest points when interpolating the value for a
	      particular cell.
	      Default:	12


NNOOTTEESS
       The amount of memory used by this program is related to the  number  of
       non-zero  data  values in the input map layer.  If the input raster map
       layer is very dense (i.e., contains many  non-zero  data  points),  the
       program may not be able to get all the memory it needs from the system.
       The time required to execute increases with the number  of  input  data
       points.


       If  the	user has a mask set, then interpolation is only done for those
       cells that fall within the mask.  However, all non-zero data points  in
       the input layer are used even if they fall outside the mask.


       This program does not work with latitude/longitude data bases.  Another
       surface generation program, named _r_._s_u_r_f_._i_d_w, should be used with lati-
       tude/longitude data bases.


       The user should refer to the manual entries for

       _r_._s_u_r_f_._i_d_w

       _r_._s_u_r_f_._c_o_n_t_o_u_r

       _s_._s_u_r_f_._i_d_w

       _s_._s_u_r_f_._r_s_t
       to  compare  this  surface  generation program with others available in
       GRASS.

SSEEEE AALLSSOO
       _r_._m_a_s_k

       _r_._s_u_r_f_._c_o_n_t_o_u_r

       _r_._s_u_r_f_._i_d_w

       _s_._s_u_r_f_._i_d_w

       _s_._s_u_r_f_._r_s_t

       _r_._s_u_r_f_._g_a_u_s_s

       _r_._s_u_r_f_._f_r_a_c_t_a_l

       _r_._s_u_r_f_._r_a_n_d_o_m

       _r_._s_u_r_f_._i_d_w_2

       _p_a_r_s_e_r

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.surf.idw2(1)
