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NAME
v.strahler - Strahler order
KEYWORDS
SYNOPSIS
v.strahler
v.strahler help
v.strahler input=name output=name dem=name [txout=string] [sloppy=float] [layer=integer] [--overwrite] [--verbose] [--quiet]
Flags:
- --overwrite
- Allow output files to overwrite existing files
- --verbose
- Verbose module output
- --quiet
- Quiet module output
Parameters:
- input=name
- Name of input vector map
- output=name
- Name for output vector map
- dem=name
- Underlying DEM
- txout=string
- Path to ASCII file where results will be written
- sloppy=float
- Threshold for distance within different nodes are considered the same node - may not work
- Default: 0.0
- layer=integer
- Layer number
- A single vector map can be connected to multiple database tables. This number determines which table to use.
- Default: 1
DESCRIPTION
v.strahler calculates the Strahler Order for all lines of a given
dendritic network. The input vector map must be free of cycles. For the
elaboration a new imported network or a network extracted from DEM by
using r.watershed can be used
(in this case the topology has to be cleaned manually). More than one
tree in the input data is allowed. No given flow direction is needed.
To find the outlet of each tree, a DEM must be given.
There are two additional scripts distributed with v.strahler:
- r.strahler.sh extracts streams from a DEM and call v.strahler
on the result.
- r.broscoe.sh computes further statistical values for a given
basin.
NOTES
Problems
This program is in beta status. It has the following shortcomings:
- The input data has to be topologically clean. Use sloppy=0.0
- Source code comments are not doxygenized (not a real problem).
How the algorithm works
In a first step, v.strahler identifies all separate networks in
the input dataset. That means, all connected lines are assigned a common
Basin ID.
Consequently, the lowest leaf of each tree is identified as outlet.
An auxiliary DEM is needed at this point.
Strahler ordering begins at each leaf of the tree with order N=1
(excluding the outlet). At a confluence, the order N(r) of the resulting
stream is equal to the highest order N(max) of the joining streams or is
raised by one if there are two or more joining streams of order N(max).
The algorithm returns an ASCII text file with columns: Category
(from input map), Line (topology), Basin, Order;
and the output map has the Strahler Order value instead of "category"
for each line, and no connection with the database.
See the also the diagrams in the documentation/ directory.
EXAMPLE
The input map (vector on DEM):
An example of the syntax in GRASS command line:
v.strahler input=esp_1@mapset output=esp_1 dem=dem_20@mapset \
txout=/home/mapset/esp_1 sloppy=0 layer=1
An extract from the resultant text file:
== Result of Strahler Order ==
Category: Line: Basin: Order:
22 1 1 4
73 2 1 1
25 3 1 4
27 4 1 4
39 5 1 1
48 6 1 1
56 7 1 4
55 8 1 2
88 9 1 4
59 10 1 1
60 11 1 1
61 12 1 2
83 13 1 2
82 14 1 1
91 15 1 1
87 16 1 4
95 17 1 2
96 18 1 1
106 19 1 1
102 20 1 1
104 21 1 4
111 22 1 1
112 23 1 3
121 24 1 3
126 25 1 1
128 26 1 3
137 27 1 3
The output map (vector on DEM) form a snapshot of GRASS display:
The output map (vector only) from Qgis (different colors for different orders):
SEE ALSO
r.watershed
AUTHOR
Florian Kindl, Univ. Innsbruck.
Modified by: Ivan Marchesini and Annalisa Minelli, Univ. Perugia.
Last changed: $Date: 2013-01-26 09:22:08 -0800 (Sat, 26 Jan 2013) $
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