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

Michael Barton Michael.Barton at asu.edu
Sat Nov 29 09:29:54 PST 2014


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




> On Nov 29, 2014, at 10:20 AM, Michael Barton <Michael.Barton at asu.edu> wrote:
> 
> Thanks. This helped.
> 
> 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
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
>> On Nov 29, 2014, at 1:23 AM, Markus Neteler <neteler at osgeo.org> wrote:
>> 
>> On Sat, Nov 29, 2014 at 6:16 AM, Michael Barton <Michael.Barton at asu.edu> wrote:
>>> I have a vector line that is divided into 12 cat values. I’d like all of the
>>> line to have a single cat value. I’ve tried v.category to no avail. If I
>>> delete all categories and then add new categories, I get 12 cats again. And
>>> I can find no other way to get a single cat for the entire line. Hopefully
>>> someone can tell what I’m missing here.
>> 
>> Please try to use
>> http://grass.osgeo.org/grass70/manuals/v.build.polylines.html
>> 
>> Markus
> 



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