[GRASS-user] v.to.points: extract start/end nodes

GRASS GRASS user
1

Hi,

I need to extract start or end nodes of lines into two separated
output maps. Unfortunately `v.to.points` doesn't seems to support it
(only `nodes` or `vertices` can be chosen). I am thinking to add such
functionality to `v.to.points`. But before that, it can be that I am
overlooking another tool which I am looking for?

Thanks for pointers in advance, Ma

--
Martin Landa
http://geo.fsv.cvut.cz/gwiki/Landa
http://gismentors.cz/mentors/landa

2

On 15/03/19 14:03, Martin Landa wrote:

Hi,

I need to extract start or end nodes of lines into two separated
output maps. Unfortunately `v.to.points` doesn't seems to support it
(only `nodes` or `vertices` can be chosen). I am thinking to add such
functionality to `v.to.points`. But before that, it can be that I am
overlooking another tool which I am looking for?

v.to.db with options start/end provides the coordinates of these points.

Moritz

3

Hi,

pá 15. 3. 2019 v 15:01 odesílatel Moritz Lennert
<mlennert@club.worldonline.be> napsal:

v.to.db with options start/end provides the coordinates of these points.

thanks, I overlooked `v.to.db`. Anyway I would still need to hack
around since `v.to.db` does not create a new output vector map. So
it's still make sense to me to implement this functionality in
`v.to.points`.

Ma

--
Martin Landa
http://geo.fsv.cvut.cz/gwiki/Landa
http://gismentors.cz/mentors/landa

4
···

On 15/03/2019 22:45, Martin Landa wrote:

Hi,

pá 15. 3. 2019 v 15:01 odesílatel Moritz Lennert
[<mlennert@club.worldonline.be>](mailto:mlennert@club.worldonline.be) napsal:


v.to.db with options start/end provides the coordinates of these points.


thanks, I overlooked `v.to.db`. Anyway I would still need to hack
around since `v.to.db` does not create a new output vector map. So
it's still make sense to me to implement this functionality in
`v.to.points`.

Ma

Whenever we get new Lidar data, I run a script to extract the streamlines network, then obtain the upstream flow accumulation area for both ends of each stream reach. The script uses a combination of v.db.update to get the x,y coordinates of both ends of each stream reach. Then these coordinates are extracted and piped into v.in.ascii, creating a new points vector. Next I get the upstream contributing area from the flow accumulation raster (v.what.rast). Finally an sql expression is constructed for db.execute to update the streams vector with upstream area for each reach from the end points vector.

So, for me, an option in v.to.points to get the start and end points would help to simplify this workflow.

Cheers, Micha

-- 
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
5

Hi,

so 16. 3. 2019 v 13:28 odesílatel Micha Silver <tsvibar@gmail.com> napsal:

So, for me, an option in v.to.points to get the start and end points would help to simplify this workflow.

done in r74283 (trunk), will be included in 7.8 release. I also find
strange that `dmax` option has defined default value (100 of map
units), could be changed in G8 see [1].

Ma

--
Martin Landa
http://geo.fsv.cvut.cz/gwiki/Landa
http://gismentors.cz/mentors/landa