NAME

r.fill.dir - Filters and generates a depressionless elevation map and a flow direction map from a given elevation layer r.fill.dir (GRASS Raster Program)

SYNOPSIS

r.fill.dir

r.fill.dir input=elev_map elevation=corrected_elev_map
direction=flow_direction_map type=agnps (answers or grass)

OPTIONS

Parameters:

input=mapname
elevation map
elevation=map
corrected elevation map
direction=map
flow direction map
type=text
type of flow direction map to be created

EXAMPLE

r.fill.dir input=ansi.elev elevation=ansi.fill.elev direction=ansi.asp type=grass

will create a depressionless elevation map ansi.fill.elev and a flow direction map ansi.asp for the type grass

ATTENTION

The type 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.

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.

NOTE

The r.fill.dir program 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.

SEE ALSO

r.direct, r.slope.aspect

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.

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.

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.

AUTHOR

Raghavan Srinivasan, Agricultural Engineering Department, Purdue University