s.medp(1)		      Grass User's Manual		     s.medp(1)



NNAAMMEE
       ss..mmeeddpp  - Median polish for a GRASS sites list.
       _(_G_R_A_S_S _S_i_t_e_s _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       ss..mmeeddpp
       ss..mmeeddpp hheellpp
       ss..mmeeddpp	[--aaeeqqss]   ssiitteess==_n_a_m_e   vveecctt==_n_a_m_e   oouuttppuutt==_n_a_m_e	 [rreeppoorrtt==_n_a_m_e]
       [tthhrreesshh==_n]

DDEESSCCRRIIPPTTIIOONN
       _s_._m_e_d_p performs median polish on an existing sites list.  The sites are
       overlayed  onto a grid (vveecctt==_n_a_m_e) and each site is associated with the
       closest node.  Therefore, sites do not necessarily have to be  oriented
       on  a  grid.  Each node may be associated with zero, one, or more sites
       and the grid may be rotated.  Also, the length of  each	box  does  not
       have to be equal to width of each box defining the grid.


       Once  sites  are  associated  with  nodes on a _p by _q grid, _p_+_q_+_1 extra
       storage locations are created (initialized to zero) to store _a_l_l,  _r_o_w,
       and  _c_o_l_u_m_n  effects.   The median of each row is removed from the data
       and added to the extra _p cells. Then, medians are removed from the data
       as  well  as  from  the _p cells containing _r_o_w effects.	The medians of
       data  in this pass are stored in the extra _q cells (_c_o_l_u_m_n effects) and
       the  median  of	the row effects is stored in the extra (_p_+_1_, _q_+_1) cell
       (_a_l_l effect). This is repeated until each successive  iteration	leaves
       each site unchanged (within a tolerance, described by [tthhrreesshh==_n]).

OOPPTTIIOONNSS
   FFllaaggss::
       --aa     Use  all sites found in the named _s_i_t_e_s file, rather than limit-
	      ing output  to  sites  falling  within  the  current  geographic
	      region.

       --ee     Store row, column, and all effects in output file.

       --ss     Write  results  to a sites list file (default is to write points
	      in a binary vector file).

       --qq     Quiet. Cut out the chatter.


   PPaarraammeetteerrss::
       ssiitteess==_n_a_m_e
	      Name of an existing sites file.

       vveecctt==_n_a_m_e
	      Name of the grid file (binary vector file).

       oouuttppuutt==_n_a_m_e
	      Name of the output file (binary vector file or sites list).

       rreeppoorrtt==_n_a_m_e
	      Name of an ASCII file which shows original and residual data  in
	      tabular form.

       tthhrreesshh==_n
	      Threshold  to  determine	when  convergence  of median polish is
	      obtained.  (default = 1).



       _s_._m_e_d_p can be run either non-interactively or interactively.  The  pro-
       gram will be run non-interactively if the user specifies the name of an
       existing _s_i_t_e_s list file, name for a _v_e_c_t file, and name of  an	_o_u_t_p_u_t
       file  using  the  form  ss..mmeeddpp [--aaeeqqss] ssiitteess==_n_a_m_e vveecctt==_n_a_m_e oouuttppuutt==_n_a_m_e
       [rreeppoorrtt==_n_a_m_e] [tthhrreesshh==_n]

       Alternately, the user can simply type ss..mmeeddpp on the command line, with-
       out  program  arguments.   In  this case, the user will be prompted for
       parameter values using the standard GRASS _p_a_r_s_e_r interface.

NNOOTTEESS
       When using the rreeppoorrtt option, the tabular report may be more  than  128
       columns	wide.  Therefore,  it may be useful to add a _T_e_X or _P_o_s_t_S_c_r_i_p_t
       wrapper before  printing  (e.g.,  eennssccrriipptt  --hh  --rr  --ffCCoouurriieerr--BBoolldd55  --pp
       rreeppoorrtt..ppss  rreeppoorrtt)  so  that the page is in landscape orientation and a
       very small font is used.


       The input vector file defining the grid should be large enough so  that
       the extreme east-west and north-south nodes (for non-rotated grids) can
       be used to store row and column effects. Otherwise, when residuals  _a_n_d
       effects	are  written  to the output file, residuals may share the same
       spatial location as effects when written to a vector output file.


       Currently, nothing is done with the residuals, but I would like	imple-
       ment  some  sort  of  analysis  of  these in the future (suggestions?).
       Kriging using these residuals as new data set is being planned.

SSEEEE AALLSSOO
       _v_._m_k_g_r_i_d

       _v_._t_r_a_n_s_f_o_r_m

       _p_a_r_s_e_r

       Cressie, Noel A. C. (1991).  _S_t_a_t_i_s_t_i_c_s _f_o_r _S_p_a_t_i_a_l _D_a_t_a, New York, NY:
       John Wiley & Sons.  pp. 186-187.

BBUUGGSS
       This  should  still be consider beta-release software.  Although I have
       repeated results shown in Cressie (1991), I  would  greatly  appreciate
       someone testing this further.


       The --ss flag is yet to be implemented.


       This  should  probably  be re-written to use points in a vector file as
       input (thus creating _v_._m_e_d_p).


       Ideally, I would also like to output three data files for plotting by a
       graphing program (e.g., _g_n_u_p_l_o_t), but I never got around to doing this.
       The classic plot is to show three surfaces:  data = trend +  residuals.
       The trend can be obtained by extrapolation and/or interpolation.


       Extrapolating  and interpolating using the row, column, and all effects
       to create a raster file would be a  nice  feature  to  include  in  the
       future.	Instead, I am considering retrieving the effects from the out-
       put file and creating the surface with separate program.


       Please send all bug fixes and comments to the author.

AAUUTTHHOORR
       James Darrell McCauley, Agricultural Engineering Purdue University

       _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.medp(1)
