r.stream.channel - GRASS GIS manual

NAME

r.stream.channel - Calculates local parameters for individual streams.

KEYWORDS

SYNOPSIS

r.stream.channel

r.stream.channel --help

r.stream.channel [-dlcm] stream_rast=name direction=name elevation=name [identifier=name] [distance=name] [difference=name] [gradient=name] [curvature=name] [memory=integer] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-d: Calculate parameters from outlet (downstream values)
-l: Calculate local values (for current cell)
-c: Calculate distance in cell count (ignored local)
-m: Use memory swap (operation is slow)
--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:

stream_rast=name [required]: Name of input raster map with stream network
direction=name [required]: Name of input raster map with flow direction
elevation=name [required]: Name of input elevation raster map
identifier=name: Name for output unique stream identifier raster map
distance=name: Name for output init/join/outlet distance raster map
difference=name: Name for output elevation init/join/outlet difference raster map
gradient=name: Name for output mean init/join/outlet gradient of stream raster map
curvature=name: Name for output local stream curvature raster map
memory=integer: Maximum memory used in memory swap mode (MB); Default: 300

DESCRIPTION
OPTIONS
EXAMPLE
SEE ALSO
AUTHOR

DESCRIPTION

The module r.stream.channel is prepared to calculate some local properties of the stream network. It is supplementary module for r.stream.order, and r.stream.distance to investigate channel subsystem. For slope subsystem parameters is r.stream.slope. It may use ordered or unordered network. It calculate parameters for every segment between it init to outlet/join to the next stream. it also may calculate parameters between outlet and segment's init. It can calculate parameters for every orders but best results are for these orders where order remains unchanged from stream init to natural outlet (Hack and Horton ordering).

OPTIONS

-d: Calculate downstream distance (from current cell DOWNSTREAM to outlet/join). Default is upstream (from current cell upstream to init/join.
-m: Only for very large data sets. Uses segment library to optimize memory consumption during analysis
stream_rast: Stream network: name of input stream map. Map may be ordered according to one of the r.stream.order ordering systems as well as unordered (with original stream identifiers). Because the streams network produced by r.watershed and r.stream.extract may slightly differ in detail it is required to use both stream and direction map produced by the same module. Non-stream cell values must be set to NULL.
direction: Flow direction: name of input direction map produced by r.watershed or r.stream.extract. If the r.stream.extract output map is used, it contains non-NULL values only in places where streams are present. NULL cells are ignored; zero and negative values are valid direction data if they vary from -8 to 8 (CCW from East in steps of 45 degrees). The direction map shall be of integer type (CELL). The region resolution and map resolution must be the same. Also the stream_rast network map must have the same resolution. If resolutions differ the module informs about it and stops. Region boundary and maps boundary may be different but it may lead to unexpected results.
elevation: Elevation: name of input elevation map. Map can be of type CELL, FCELL or DCELL. It is not restricted to resolution of region settings as streams and direction.
distance: Upstream distance of current cell to the init/join. Flag modifications:
-d: downstream distance of current cell to the join/outlet;
-l: local distance between current cell and next cell. In most cases cell resolution and sqrt2 of cell resolution. useful when projection is LL or NS and WE resolutions differs. Flag -d ignored
-c: distance in cells. Map is written as double. Use r.mapcalc to convert to integer. Flags -l and -d ignored.
difference: Upstream elevation difference between current cell to the init/join. It we need to calculate parameters different than elevation. If we need to calculate different parameters than elevation along streams (for example precipitation or so) use necessary map as elevation. Flag modifications:
-d: downstream difference of current cell to the join/outlet;
-l: local difference between current cell and next cell. With flag calculates difference between previous cell and current cell
-c: Ignored.
gradient: Upstream mean gradient between current cell and the init/join. Flag modifications:
-d: downstream mean gradient between current cell and the join/outlet;
-l: local gradient between current cell and next cell. Flag -d ignored
-c: Ignored.
curvature: Local stream course curvature of current cell. Calculated according formula: first_derivative/(1-second_derivative²)^3/2 Flag modifications:
-d: ignored;
-l: Ignored.
-c: Ignored.
identifier: Integer map: In ordered stream network there are more than one segment (segment: a part of the network where order remains unchanged) with the same order. To identify particular segments (for further analysis) every segment receive his unique identifier.

EXAMPLE

This example shows how to visualise the change of gradient map along the main stream of the catchment:

g.region -p -a raster=elevation
r.watershed elevation=elevation threshold=10000 drainage=direction stream=streams
r.stream.order streams=streams direction=direction hack=hack
r.stream.channel streams=hack direction=direction elevation=elevation \
  identifier=stream_identifier distance=stream_distance gradient=stream_gradient

# Eg., 495 is a stream identifier. May be different in different situation
r.mapcalc "stgrad = if(stream_identifier==495,float(stream_gradient),null())"
r.mapcalc "stdist = if(stream_identifier==495,float(stream_distance),null())"

# Use R for plotting
R
library(spgrass6)
r=readRAST6(c("stdist","stgrad"),NODATA=-9999)
p=subset(r@data,!is.na(r@data$dist))
sorted=p[order(p$stdist),]
plot(sorted,stdist~stgrad,type="l")

AUTHOR

Jarek Jasiewicz, Adam Mickiewicz University, Geoecology and Geoinformation Institute.

SOURCE CODE

Available at: r.stream.channel source code (history)