xenial (1) r.fill.dir.1grass.gz

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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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