r.fill.dir(1)		      Grass User's Manual		 r.fill.dir(1)



NNAAMMEE
       rr..ffiillll..ddiirr   - Filters and generates a depressionless elevation map and
       a flow direction map from a given elevation layer
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ffiillll..ddiirr


	rr..ffiillll..ddiirr [[--ff]] iinnppuutt==_n_a_m_e eelleevvaattiioonn==_n_a_m_e
	      ddiirreeccttiioonn==_n_a_m_e [aarreeaass==_n_a_m_e] [ttyyppee==_n_a_m_e]

OOPPTTIIOONNSS
   FFllaaggss::
       --ff     find unresolved areas only (don't generate filled DEM  except  1
	      pixel sinks)


   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      elevation map

       eelleevvaattiioonn==_n_a_m_e
	      corrected elevation map (depression less)

       ddiirreeccttiioonn==_n_a_m_e
	      flow direction map

       ttyyppee==_n_a_m_e
	      type of flow direction map to be created

       aarreeaass==_n_a_m_e
	      Output raster map of problem areas


DDEESSCCRRIIPPTTIIOONN
       rr..ffiillll..ddiirr  filters  and generates a depressionless elevation map and a
       flow direction map from a given elevation layer.

EEXXAAMMPPLLEE
       rr..ffiillll..ddiirr iinnppuutt==_a_n_s_i_._e_l_e_v eelleevvaattiioonn==_a_n_s_i_._f_i_l_l_._e_l_e_v ddiirreeccttiioonn==_a_n_s_i_._a_s_p



       will create a depressionless (sinkless)	elevation  map	ansi.fill.elev
       and a flow direction map ansi.asp for the type "grass".


AATTTTEENNTTIIOONN
       _T_h_e  _t_y_p_e  is the type of format at which the user wishes to create the
       flow direction map. The _a_g_n_p_s format gives category  values  from  1-8,
       with  1	facing north and increasing values in the clockwise direction.
       The _a_n_s_w_e_r_s format gives category values from  0-360  degrees,  with  0
       (360) facing east and values increasing in the counter clockwise direc-
       tion at 45 degree increments. The _g_r_a_s_s format gives the same  category
       values as the _r_._s_l_o_p_e_._a_s_p_e_c_t program.


       _T_h_e  _m_e_t_h_o_d adopted to filter the elevation map and rectify it is based
       on the paper titled "Software Tools to Extract Structure  from  Digital
       Elevation Data for Geographic Information System Analysis" by S.K. Jen-
       son and J.O. Domingue (1988).


       The procedure takes an elevation layer as input and initially fills all
       the depressions with one pass across the layer. Next the flow direction
       algorithm tries to find a unique direction for each cell. If the water-
       shed program detects areas with pothholes, it delineates this area from
       the rest of the area and once again the depressions  are  filled  using
       the  neighborhood  technique  used  by  the flow direction routine. The
       final output will be a depressionless elevation layer and a unique flow
       direction layer.


       This  (D8)  flow algorithm performs as follows: At each raster cell the
       code determines the slope to  each  of  the  8  surrounding  cells  and
       assigns	the  flow  direction to the highest slope out of the cell.  If
       there is more than one equal, non-zero slope then the  code  picks  one
       direction  based  on  preferences that are hard-coded into the program.
       If the highest slope is flat and in more than one  direction  then  the
       code  first  tries to select an alternative based on flow directions in
       the adjacent cells.  It iteratives that process, effectively  propagat-
       ing  flow directions from areas where the directions are known into the
       area where the flow direction can't otherwise be resolved.


       The flow direction map can be encoded in either ANSWERS (Beasley et.al,
       1982) or AGNPS (Young et.al, 1985) form, so that it can be readily used
       as input to these hydrologic models. The resulting depressionless  ele-
       vation  layer  can further be manipulated for deriving slopes and other
       attributes required by the hydrologic models.


       In case of local problems, those unfilled areas can be  stored  option-
       ally.   Each  unfilled  area  in  this  maps is numbered. The flag _"_-_f_"
       instructs the program to fill single-cell pits but  otherwise  to  just
       find  the  undrained areas and exit. With the _"_-_f_" flag set the program
       writes an elevation map with just single-cell pits filled, a  direction
       map with unresolved problems and a map of the undrained areas that were
       found but not filled. This option was included because filling DEMs was
       often  not  the best way to solve a drainage problem. These options let
       the user get a partially-fixed elevation map,  identify	the  remaining
       problems and fix the problems appropriately.

NNOOTTEE
       _T_h_e _r_._f_i_l_l_._d_i_r program is sensitive to the ccuurrrreenntt wwiinnddooww sseettttiinngg. Thus
       the program can be used to generate a flow direction map for  any  sub-
       area  within  the  full map layer. Also, _r_._f_i_l_l_._d_i_r is sensitive to any
       _m_a_s_k in effect.


       In some cases it may be necessary to run r.fill.dir  repeatedly	(using
       output  from  one  run  as input to the next run) before all of problem
       areas are filled.

SSEEEE AALLSSOO
       _r_._d_i_r_e_c_t_, _r_._f_i_l_l_n_u_l_l_s_, _r_._s_l_o_p_e_._a_s_p_e_c_t


       Jenson, S.K., and J.O. Domingue. 1988. Extracting topographic structure
       from  digital  elevation  model	data for geographic information system
       analysis. Photogram. Engr. and Remote Sens. 54: 1593-1600.


       Beasley, D.B. and L.F. Huggins. 1982. ANSWERS  (areal  nonpoint	source
       watershed  environmental  response  simulation):  User's  manual.  U.S.
       EPA-905/9-82-001, Chicago, IL, 54 p.


       Young, R.A., C.A. Onstad, D.D. Bosch and W.P. Anderson. 1985.  Agricul-
       tural nonpoint surface pollution models (AGNPS) I and II model documen-
       tation. St. Paul: Minn. Pollution control Agency and  Washington  D.C.,
       USDA-Agricultural Research Service.

AAUUTTHHOORR
       Fortran	version: Raghavan Srinivasan, Agricultural Engineering Depart-
       ment, Purdue University

       Rewrite to C with enhancements: Roger S. Miller

       _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							 r.fill.dir(1)
