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]  [--verbose]  [--quiet]
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18   Flags:
19       -f
20           find unresolved areas only
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22       --overwrite
23           Allow output files to overwrite existing files
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25       --verbose
26           Verbose module output
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28       --quiet
29           Quiet module output
30
31   Parameters:
32       input=name
33           Name of existing raster map containing elevation surface
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35       elevation=string
36           Output elevation raster map after filling
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38       direction=string
39           Output direction raster map
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41       areas=string
42           Output raster map of problem areas
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44       type=string
45           Output aspect direction format (agnps, answers, or grass)
46           Default: grass
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DESCRIPTION

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

53
54       r.fill.dir input=ansi.elev elevation=ansi.fill.elev direction=ansi.asp
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56
57       will create a depressionless (sinkless)  elevation  map  ansi.fill.elev
58       and a flow direction map ansi.asp for the type "grass".
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ATTENTION

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

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

138       Fortran  version: Raghavan Srinivasan, Agricultural Engineering Depart‐
139       ment, Purdue University
140       Rewrite to C with enhancements: Roger S. Miller
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142       Last changed: $Date: 2006-04-20 23:31:24 +0200 (Thu, 20 Apr 2006) $
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144       Full index
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146       © 2003-2008 GRASS Development Team
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150GRASS 6.3.0                                                      r.fill.dir(1)