NAME
r.stream.snap - Snap point to modelled stream network.
Input can be stream network, point vector map with outlets or outlet coordinates.
KEYWORDS
raster,
hydrology,
stream network,
basins creation
SYNOPSIS
r.stream.snap
r.stream.snap --help
r.stream.snap input=name output=name [stream_rast=name] [accumulation=name] [threshold=float] [radius=integer] [memory=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
- --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 vector map
- Name of input vector points map
- output=name [required]
- Name for output vector points map
- stream_rast=name
- Name of input raster map with stream network
- accumulation=name
- Name of input accumulation raster map
- threshold=float
- Minimum accumulation threshold to snap
- Default: -1
- radius=integer
- Maximum distance to snap (in cells)
- Default: 1
- memory=integer
- Max memory used (MB)
- Default: 300
The module r.stream.snap is a supplementary module for
r.stream.extract and
r.stream.basins to correct
the position of outlets or stream initial points as they do not lie on
the streamlines.
For the outlet, the point is snapped to the nearest point which lies on
the streamline.
For the stream initial points, when there is a small tributary near
the main stream, the accumulation threshold shall be high enough to
force the program ignoring this tributary and snap to the main stream.
If there is no accumulation map, the points will be snapped to the
nearest stream line, which in particular situations may be wrong.
Because the r.stream.* modules are prepared to work with MFD
accumulation maps, both stream network and accumulation map are
necessary.
While it is assumed that the accumulation map is a MFD map, if the
stream network is not supplied, the snap point is calculated in
different way: the threshold is used to select only those points in the
search radius which have accumulation value greater than the given
threshold. The next mean value of these points is calculated and its
value is taken as a new threshold. This procedure guarantees that
points are snapped to the center of the stream tube. While for inits
small thresholds are in use, it is probable that points were snapped to
the stream tube border instead of its center.
It is strongly recommended to use both stream network (even
pre-generated with small accumulation threshold) and accumulation
raster map, than accumulation or stream raster map only.
- stream_rast
- Stream network created
by r.stream.extract or
r.watershed. If used, the
points are snapped to the nearest streamline point whose accumulation
is greater than the threshold. If the accumulation is not used, the
point is snapped to the nearest stream.
- accumulation
- Accumulation map created with
r.watershed and used to
generate the stream network with
r.stream.extract. If
the stream network is not used, the point is adaptively snapped to the
point where the value is greater than mean values of accumulation
greater than given threshold in a search radius. See the description for
details.
- radius
- Search radius (in cells). If there are no streams in the search
radius, the point is not snapped. If there are no cells with
accumulation greater than accumulation threshold, the point also is
not snapped.
- threshold
- Minimum value of accumulation to snap the point. This option is
added to the snap stream inits to the stream tubes
and to distinguish between local tributaries and main streams.
- input
- Vector file containing outlets or inits as vector points. Only
point's categories are used. Any table attached to it is
ignored. Every point shall have its own unique category.
- output
- Vector file containing outlets or inits after snapping. On layer 1,
the original categories are preserved, on layer 2 there are four
categories which mean:
- skipped (not in use yet)
- unresolved (points remain unsnapped due to lack of streams in search radius
- snapped (points snapped to streamlines)
- correct (points which remain on their original position, which were
originally corrected)
g.region -p -a raster=elevation
r.watershed elevation=elevation threshold=10000 drainage=dirs stream=streams accumulation=accum
# snap a point sampled in the riverine landscape to the calculated river network
r.stream.snap input=mysampleoutlet output=mysampleoutlet_snapped stream_rast=streams accumulation=accum
r.mapcalc,
r.patch,
r.reclass,
r.stream.extract,
r.stream.basins,
r.stream.channel,
r.stream.order,
r.stream.segment,
r.stream.slope,
r.stream.stats,
r.stream.distance,
r.watershed
See
also r.streams.*
modules wiki page.
Jarek Jasiewicz, Adam Mickiewicz University, Geoecology and Geoinformation
Institute.
SOURCE CODE
Available at:
r.stream.snap source code
(history)
Latest change: Thursday Aug 15 15:27:16 2024 in commit: a0e37beaf0ce8a4cc6ec615b6d3d40e39f9d725f
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GRASS Development Team,
GRASS GIS 8.4.1dev Reference Manual