On 30/11/14 06:28, Michael Barton wrote:
____________________
C. Michael Barton
Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Head, Graduate Faculty in Complex Adaptive Systems Science
Arizona State University
voice: 480-965-6262 (SHESC), 480-965-8130/727-9746 (CSDC)
fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
Thanks César,
This is pretty much what I’m doing. However, it is not that simple, it
turns out.
First, for a stream profile, you want to isolate a single watercourse.
r.stream.extract creates a stream network. Getting stream order does not
help with profiling, however.
I looked at r.stream.distance. But this calculates distance from each
stream junction. I want it for the entire course of the selected
stream—from headwaters to outlet. That is the only way to graph a stream
profile for the entire stream.
Once I have a set of points with the distance from the beginning or the
end of the line stored as an attribute for each point, the rest is easy.
It is getting to this step that is hard.
If a line is composed of multiple segments—as is the case for any line
created with r.stream.extract or r.watershed, and also with r.drain
surprisingly—there is nothing that will ignore all of these segments and
just give me the distance along the line from one end to the other. This
is the case with v.to.points
As MarkusN said: you have to use v.build.polylines with cats=first, but
then it is easy to get total length with v.to.db or v.to.points if that
is what you need (or many other options (get end node coordinates and
use v.distance 'to_along' or MarkusM's suggestion: v.net.distance from
start to end node along the stream).
Here's an example in the NC dataset, using r.stream.order to approximate
the main stream:
g.region n=227440 s=221640 w=630220 e=637220 res=10
r.watershed --overwrite elevation=elevation@PERMANENT threshold=10000
accumulation=accum drainage=direction stream=streams
r.stream.order --overwrite stream_rast=streams@user1
direction=direction@user1 elevation=elevation@PERMANENT
accumulation=accum@user1 stream_vect=streams horton=horton
v.extract --overwrite input=streams@user1 where=horton=3 output=main_stream
v.build.polylines --overwrite input=main_stream@user1
output=main_stream_poly cats=first
then: v.to.db (result=11312.5) or
v.to.points input=main_stream@user1 output=main_stream_points dmax=1
db.select sql="select round(max(along)) from main_stream_points_2"
round(max(along))
11312.5
Moritz
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