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  approximation (weighted averaging) tech-
       niques. 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  meth-
       ods, numerical approximation allows representation of more
       complex surfaces (particularly those with  anomalous  fea-
       tures), restricts the spatial influence 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 interface.

OOPPTTIIOONNSS
   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      Name of an input site list file that contains a set
	      of irregularly 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 containing 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 inter-
	      polation.
	      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., con-
       tains 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 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)
