r.carve - GRASS GIS manual

NAME

r.carve - Generates stream channels.
Takes vector stream data, transforms it to raster and subtracts depth from the output DEM.

KEYWORDS

raster, hydrology

SYNOPSIS

r.carve

r.carve --help

r.carve [-n] raster=name vector=name output=name [points=name] [width=float] [depth=float] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-n: No flat areas allowed in flow direction
--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:

raster=name [required]: Name of input raster elevation map
vector=name [required]: Name of input vector map containing stream(s); Or data source for direct OGR access
output=name [required]: Name for output raster map
points=name: Name for output vector map for adjusted stream points
width=float: Stream width (in meters); Default is raster cell width
depth=float: Additional stream depth (in meters)

DESCRIPTION
NOTES
EXAMPLE
KNOWN ISSUES
REFERENCES
SEE ALSO
AUTHORS

DESCRIPTION

r.carve accepts vector stream data as input, transforms them to raster, and subtracts a default-depth + additional-depth from a DEM. If the given width is more than 1 cell, it will carve the stream with the given width. With the -n flag it should eliminate all flat cells within the stream, so when and if the water gets into the stream it will flow. The points option generates x,y,z for points which define the stream with the z-value of the bottom of the carved-in stream. These points can then be combined with contours to interpolate a new DEM with better representation of valleys.

NOTES

r.carve does not create a depressionless DEM because many depressions are in flat areas and not in the streams.

EXAMPLE

North Carolina sample dataset:

# set computational region
g.region raster=elev_lid792_1m -p

# digitize a ditch for the farm pond
echo "L  3 1
 638692.93595422 220198.90026383
 638737.42270627 220149.74706926
 638984.43306379 220148.19158842
 1     1" | v.in.ascii -n input=- output=ditch format=standard

# visualize original data
d.mon wx0
d.rast elev_lid792_1m
d.vect ditch

# carve
r.carve raster=elev_lid792_1m vector=ditch output=carved_dem width=3 depth=0.5

# visualize resulting carved DEM map
d.rast carved_dem

# visualize
r.relief input=elev_lid792_1m output=elev_lid792_1m_shaded
r.relief input=carved_dem output=carved_dem_shaded
d.rast elev_lid792_1m_shaded
d.erase
d.rast carved_dem_shaded

# flow accumulation
r.watershed elevation=elev_lid792_1m accumulation=elev_lid792_1m_accum
r.watershed elevation=carved_dem accumulation=carved_dem_accum
d.rast elev_lid792_1m_accum
d.erase
d.rast carved_dem_accum

# differences
r.mapcalc "accum_diff = elev_lid792_1m_accum - carved_dem_accum"
r.colors accum_diff color=differences
d.erase
d.rast accum_diff

Fig: Original 1m LiDAR based DEM with vector streams map on top	Fig: Original 1m LiDAR based DEM shown as shaded terrain
Fig: Carved 1m LiDAR based DEM	Fig: Carved 1m LiDAR based DEM shown as shaded terrain
Fig: Flow accumulation in original 1m LiDAR based DEM	Fig: Flow accumulation in carved 1m LiDAR based DEM