.TH r.fill.dir 1grass "" "GRASS 6.4.2" "Grass User's Manual"
.SH NAME
\fI\fBr.fill.dir\fR\fR  - Filters and generates a depressionless elevation map and a flow direction map from a given elevation raster map.
.SH KEYWORDS
raster, hydrology
.SH SYNOPSIS
\fBr.fill.dir\fR
.br
\fBr.fill.dir help\fR
.br
\fBr.fill.dir\fR [-\fBf\fR] \fBinput\fR=\fIname\fR \fBelevation\fR=\fIstring\fR \fBdirection\fR=\fIstring\fR  [\fBareas\fR=\fIstring\fR]   [\fBtype\fR=\fIstring\fR]   [--\fBoverwrite\fR]  [--\fBverbose\fR]  [--\fBquiet\fR] 
.SS Flags:
.IP "\fB-f\fR" 4m
.br
Find unresolved areas only
.IP "\fB--overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB--verbose\fR" 4m
.br
Verbose module output
.IP "\fB--quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR" 4m
.br
Name of existing raster map containing elevation surface
.IP "\fBelevation\fR=\fIstring\fR" 4m
.br
Output elevation raster map after filling
.IP "\fBdirection\fR=\fIstring\fR" 4m
.br
Output direction raster map
.IP "\fBareas\fR=\fIstring\fR" 4m
.br
Output raster map of problem areas
.IP "\fBtype\fR=\fIstring\fR" 4m
.br
Output aspect direction format (agnps, answers, or grass)
.br
Default: \fIgrass\fR
.PP
.SH DESCRIPTION
\fIr.fill.dir\fR filters and generates a depressionless
elevation map and a flow direction map from a given raster elevation map.
.SH NOTES
The \fBtype\fR parameter is the type of format at which the user wishes to create
the flow direction map. The \fIagnps\fR format gives category values from
1-8, with 1 facing north and increasing values in the clockwise direction.
The \fIanswers\fR 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 \fIgrass\fR format gives the same category
values as the \fIr.slope.aspect\fR
program.
.PP
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).
.PP
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.
.PP
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. \fIr.fill.dir\fR 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.
.PP
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.
.PP
In case of local problems, those unfilled areas can be stored optionally.
Each unfilled area in this maps is numbered. The \fB-f\fR flag
instructs the program to fill single-cell pits but otherwise to just find
the undrained areas and exit. With the \fB-f\fR 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.
.PP
\fIr.fill.dir\fR 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, \fIr.fill.dir\fR is
sensitive to any \fImask\fR in effect.
.PP
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.
.SH EXAMPLE
\fC
.DS
.br
r.fill.dir input=ansi.elev elevation=ansi.fill.elev direction=ansi.asp
.br
.DE
\fR
.PP
will create a depressionless (sinkless) elevation map ansi.fill.elev and a flow
direction map ansi.asp for the type "grass".
.SH SEE ALSO
\fI
r.fillnulls,
r.slope.aspect\fR
.PP
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.
.PP
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.
.PP
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.
.PP
.SH AUTHOR
Fortran version:
Raghavan Srinivasan, Agricultural Engineering Department, Purdue
University
.br
Rewrite to C with enhancements:
Roger S. Miller
.PP
\fILast changed: $Date: 2008-05-15 20:59:22 +0200 (Thu, 15 May 2008) $\fR
.PP
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.PP
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