[GRASS-user] how to change all cats in a vector line

[Michael Barton]

____________________
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 and v.fixed.segmentpoints. v.profile might do the job but it is not available for GRASS 7.

Michael










On Nov 29, 2014, at 10:02 PM, grass-user-request at lists.osgeo.org<mailto:grass-user-request at lists.osgeo.org> wrote:

From: César Augusto Ramírez Franco <caesarivs at gmail.com<mailto:caesarivs at gmail.com>>
To: GRASS User List <grass-user at lists.osgeo.org<mailto:grass-user at lists.osgeo.org>>
Date: November 29, 2014 at 9:13:43 PM MST
Subject: Re: [GRASS-user] how to change all cats in a vector line


Hello Michael
You could use r.stream.order after r.stream.extract to get your stream network ordered, and then, after running r.thin on the ordered stream network, convert it to vector using r.to.vect with the -v flag, that way, each order is a cat, you can them use v.to.points or the add-on suggested below to get topologically-correct points along the stream network, you could also use r.stream.distance and upload distance and elevation to each point using v.what.rast
I usually run R from within GRASS and use the spgrass6 library to read the vector map and analyze the data there
Regards
César.

El sáb, 29 de noviembre de 2014 06:29 p.m., Helmut Kudrnovsky <hellik at web.de<mailto:hellik at web.de>> escribió:
Michael Barton wrote
> Hi Markus,
>
> What I'm trying to do is start with a raster stream map from r.drain and
> convert it to a sequence of vector points, where each point has
> information as to its position along the stream. I then use the points for
> sampling a stream profile and related information. Oddly enough, with all
> of the very useful stream analysis modules, there is nothing I could find
> to generate the data for a stream profile (distance from outlet or from
> headwaters vs. elevation).
>
> v.to.points does a nice job of creating a sequence of evenly spaced points
> with information about their location along a line (the "along" field).
> BUT, if the line is composed of multiple segments or even if it has an
> irregularity in it, the "along" values start over again from 0. The only
> way I can use it is if I have a very clean and continuous vector line with
> only a single cat.
>
> This has proven surprisingly difficult to obtain reliably from my raster
> stream map. So far, the only way has been to do a two sequences of v.clean
> (with thresholds 1.5 X the raster resolution) and v.build.polylines. If
> you have any better suggestion, I'd love to hear it.
>
> Thanks again for the polylines idea. That was a big help.
>
> Michael
> ____________________
> 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<http://csdc.asu.edu/>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20141130/a23372d2/attachment-0001.html>