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



NNAAMMEE
       ss..ssuurrff..iiddww  - Surface interpolation from sites data by Inverse Distance
       Squared Weighting.
       _(_G_R_A_S_S Sites Program)

SSYYNNOOPPSSIISS
       ss..ssuurrff..iiddww [[--nn]] iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e [[nnppooiinnttss==_c_o_u_n_t]] [[ffiieelldd==_n_u_m_b_e_r]]

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 [[--nn]] iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e [[nnppooiinnttss==_c_o_u_n_t]] [[ffiieelldd==_n_u_m_b_e_r]]

       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
   FFllaaggss::
       --nn     Don't index sites by cell. (for very large  regions;  uses  less
	      memory, but is very slow if there is a large number of sites)


   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	   Name  of  an  input	site list file that contains sites with one or
	   more floating point attributes.

       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 interpolation.
	   Default: 12

       ffiieelldd==_n_u_m_b_e_r
	   Number of floating point attribute to use for interpolation.
	   Default: 1


NNOOTTEESS
       The  amount  of memory used by this program is related to the number of
       sites in the current region.  If the site list  is  very  dense	(i.e.,
       contains  many data points), the program may not be able to get all the
       memory it needs from the system.   The  time  required  to  execute  is
       related to the resolution of the current region, after an initial delay
       determined by the time taken to read the input sites file.


       If the user has a mask set, then interpolation is only done  for  those
       cells  that  fall  within  the  mask. However, all sites in the current
       region are used even if they fall outside the mask. Sites  outside  the
       current	region	are not used in the interpolation. A larger region may
       be set and a mask used to limit interpolation to a smaller area	if  it
       is desired to use sites from outside the region in the interpolation.


       If  more than _c_o_u_n_t sites fall into one target raster cell, the mean of
       all the site values will determine the cell value (unless the  -n  flag
       is  specifed,  in which case only the _c_o_u_n_t sites closest to the centre
       of the cell will be interpolated).

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
       Improved  algorithm  (indexes sites according to cell and ignores sites
       outside current region) by Paul Kelly

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_3_/_0_8_/_2_0 _0_8_:_1_0_:_1_3 _$



GRASS 5.0							 s.surf.idw(1)
