DESCRIPTION

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

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")

SEE ALSO

AUTHOR

Last changed: $Date$