Provided by: grass-doc_7.0.3-1build1_all 
NAME
r.fill.dir - Filters and generates a depressionless elevation map and a flow direction map from a given
elevation raster map.
KEYWORDS
raster, hydrology
SYNOPSIS
r.fill.dir
r.fill.dir --help
r.fill.dir [-f] input=name output=name direction=name [areas=name] [format=string] [--overwrite]
[--help] [--verbose] [--quiet] [--ui]
Flags:
-f
Find unresolved areas only
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input elevation raster map
output=name [required]
Name for output depressionless elevation raster map
direction=name [required]
Name for output flow direction map for depressionless elevation raster map
areas=name
Name for output raster map of problem areas
format=string
Aspect direction format
Options: agnps, answers, grass
Default: grass
DESCRIPTION
r.fill.dir filters and generates a depressionless elevation map and a flow direction map from a given
raster elevation map.
NOTES
The format parameter is the type of format at which the user wishes to create the flow direction map. The
agnps format gives category values from 1-8, with 1 facing north and increasing values in the clockwise
direction. The answers format gives category values from 0-360 degrees, with 0 (360) facing east and
values increasing in the counter clockwise direction at 45 degree increments. The grass format gives the
same category values as the r.slope.aspect program.
The method 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. Jenson 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 watershed 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. r.fill.dir
iteratates that process, effectively propagating 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 elevation 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 optionally. Each unfilled area in this
maps is numbered. The -f flag 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.
r.fill.dir is sensitive to the current window setting. Thus the program can be used to generate a flow
direction map for any sub-area within the full map layer. Also, r.fill.dir is sensitive to any mask 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.
EXAMPLE
r.fill.dir input=ansi.elev output=ansi.fill.elev direction=ansi.asp
Will create a depressionless (sinkless) elevation map ansi.fill.elev and a flow direction map ansi.asp
for the type "grass".
REFERENCES
• 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.
• 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.
• Young, R.A., C.A. Onstad, D.D. Bosch and W.P. Anderson. 1985. Agricultural nonpoint surface
pollution models (AGNPS) I and II model documentation. St. Paul: Minn. Pollution control Agency
and Washington D.C., USDA-Agricultural Research Service.
SEE ALSO
r.fillnulls, r.slope.aspect
AUTHORS
Fortran version: Raghavan Srinivasan, Agricultural Engineering Department, Purdue University
Rewrite to C with enhancements: Roger S. Miller
Last changed: $Date: 2014-11-28 17:25:40 +0100 (Fri, 28 Nov 2014) $
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