r.fill.dir(1)

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

6       r.fill.dir   - Filters and generates a depressionless elevation map and
7       a flow direction map from a given elevation layer
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KEYWORDS

10       raster
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SYNOPSIS

13       r.fill.dir
14       r.fill.dir help
15       r.fill.dir   [-f]    input=name    elevation=string    direction=string
16       [areas=string]   [type=string]   [--overwrite]
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18   Flags:
19       -f  find unresolved areas only
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21       --overwrite
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23   Parameters:
24       input=name
25           Name of existing raster map containing elevation surface
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27       elevation=string
28           Output elevation raster map after filling
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30       direction=string
31           Output direction raster map
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33       areas=string
34           Output raster map of problem areas
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36       type=string
37           Output  aspect direction format (agnps, answers, or grass) Default:
38           grass
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DESCRIPTION

41       r.fill.dir filters and generates a depressionless elevation map  and  a
42       flow direction map from a given elevation layer.
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EXAMPLE

45
46       r.fill.dir input=ansi.elev elevation=ansi.fill.elev direction=ansi.asp
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49       will  create  a  depressionless (sinkless) elevation map ansi.fill.elev
50       and a flow direction map ansi.asp for the type "grass".
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ATTENTION

53       The type is the type of format at which the user wishes to  create  the
54       flow  direction  map.  The agnps format gives category values from 1-8,
55       with 1 facing north and increasing values in the  clockwise  direction.
56       The  answers  format  gives  category values from 0-360 degrees, with 0
57       (360) facing east and values increasing in the counter clockwise direc‐
58       tion  at 45 degree increments. The grass format gives the same category
59       values as the r.slope.aspect program.
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61       The method adopted to filter the elevation map and rectify it is  based
62       on  the  paper titled "Software Tools to Extract Structure from Digital
63       Elevation Data for Geographic Information System Analysis" by S.K. Jen‐
64       son and J.O. Domingue (1988).
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66       The procedure takes an elevation layer as input and initially fills all
67       the depressions with one pass across the layer. Next the flow direction
68       algorithm tries to find a unique direction for each cell. If the water‐
69       shed program detects areas with pothholes, it delineates this area from
70       the  rest  of  the area and once again the depressions are filled using
71       the neighborhood technique used by  the  flow  direction  routine.  The
72       final output will be a depressionless elevation layer and a unique flow
73       direction layer.
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75       This (D8) flow algorithm performs as follows: At each raster  cell  the
76       code  determines  the  slope  to  each  of  the 8 surrounding cells and
77       assigns the flow direction to the highest slope out of  the  cell.   If
78       there  is  more  than one equal, non-zero slope then the code picks one
79       direction based on preferences that are hard-coded  into  the  program.
80       If  the  highest  slope is flat and in more than one direction then the
81       code first tries to select an alternative based on flow  directions  in
82       the  adjacent cells.  It iteratives that process, effectively propagat‐
83       ing flow directions from areas where the directions are known into  the
84       area where the flow direction can't otherwise be resolved.
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86       The flow direction map can be encoded in either ANSWERS (Beasley et.al,
87       1982) or AGNPS (Young et.al, 1985) form, so that it can be readily used
88       as  input to these hydrologic models. The resulting depressionless ele‐
89       vation layer can further be manipulated for deriving slopes  and  other
90       attributes required by the hydrologic models.
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92       In  case  of local problems, those unfilled areas can be stored option‐
93       ally.  Each unfilled area in this  maps  is  numbered.  The  flag  "-f"
94       instructs  the  program  to fill single-cell pits but otherwise to just
95       find the undrained areas and exit. With the "-f" flag set  the  program
96       writes  an elevation map with just single-cell pits filled, a direction
97       map with unresolved problems and a map of the undrained areas that were
98       found but not filled. This option was included because filling DEMs was
99       often not the best way to solve a drainage problem. These  options  let
100       the  user  get  a partially-fixed elevation map, identify the remaining
101       problems and fix the problems appropriately.
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NOTE

104       The r.fill.dir program is sensitive to the current window setting. Thus
105       the  program  can be used to generate a flow direction map for any sub-
106       area within the full map layer. Also, r.fill.dir is  sensitive  to  any
107       mask in effect.
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109       In  some  cases it may be necessary to run r.fill.dir repeatedly (using
110       output from one run as input to the next run)  before  all  of  problem
111       areas are filled.
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AUTHOR

130       Fortran version: Raghavan Srinivasan, Agricultural Engineering  Depart‐
131       ment, Purdue University
132       Rewrite to C with enhancements: Roger S. Miller
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134       Last changed: $Date: 2006/04/20 21:31:23 $
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136       Full index
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140GRASS 6.2.2                                                      r.fill.dir(1)