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

[Helmut Kudrnovsky]

Michael Barton wrote
> Hi Markus, 
> 
> What I'm trying to do is start
> http://grasswiki.osgeo.org/wiki/AddOns/GRASS7/vector#v.fixed.segmentpointsa
> 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@

> > 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@

> > wrote:
>>> 
>>> On Sat, Nov 29, 2014 at 6:16 AM, Michael Barton <

> Michael.Barton@

> > 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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for points along a vector with a fixed distance between the points, see the
addon

 http://grasswiki.osgeo.org/wiki/AddOns/GRASS7/vector#v.fixed.segmentpoints




-----
best regards
Helmut
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