s.surf.idw(1)		      Grass User's Manual		 s.surf.idw(1)



NNAAMMEE
       ss..ssuurrff..iiddww  - Surface interpolation from sites data by Inverse Distance
       Weighted algorithm.
       _(_G_R_A_S_S Raster Program)

SSYYNNOOPPSSIISS
       ss..ssuurrff..iiddww iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e [[nnppooiinnttss==_c_o_u_n_t]] [[ffiieelldd==_v_a_l_u_e]]

DDEESSCCRRIIPPTTIIOONN
       _s_._s_u_r_f_._i_d_w 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.


       This program allows the user to use a GRASS site list file, rather than
       a raster map layer, as input.


       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:


       ss..ssuurrff..iiddww iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e [[nnppooiinnttss==_c_o_u_n_t]] [[ffiieelldd==_v_a_l_u_e]]

       Alternately,  the  user can simply type ss..ssuurrff..iiddww on the command line,
       without program arguments. In this case, the user will be prompted  for
       needed inputs and option choices using the standard GRASS _p_a_r_s_e_r inter-
       face.

OOPPTTIIOONNSS
   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      Name of an input site list file 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 site list file.

       nnppooiinnttss==_c_o_u_n_t
	      The number of points to use for interpolation.  By default,  the
	      12 nearest points are used for interpolation.
	      Default: 12

       ffiieelldd  Number of z-field attribute to use for calculation default: 1



NNOOTTEESS
       The  amount  of memory used by this program is related to the number of
       non-zero data values in the iinnppuutt sites list file.  If the  iinnppuutt  site
       list is very dense (i.e., contains many non-zero data points), the pro-
       gram 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 iinnppuutt map are used even if they fall outside the mask.


       If two or more sites fall into one target raster cell,  the  last  site
       value will determine the cell value (no warning yet).

SSEEEE AALLSSOO
       _d_._s_i_t_e_s

       _g_._r_e_g_i_o_n

       _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

       _r_._s_u_r_f_._i_d_w_2

       _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

       _v_._s_u_r_f_._r_s_t

       _s_._s_u_r_f_._r_s_t

       _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_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_5 _$



GRASS 5.0							 s.surf.idw(1)
