[GRASS-dev] How to sample raster values along a vector line?

GRASS GIS GRASS GIS developer
1

Hi devs,

I somehow don't get how to sample values from a raster map along a
vector line which is several pixels long.
In essence, something like this
#1852: r.profile: accept lines vector map as profile
https://trac.osgeo.org/grass/ticket/1852

Issues:
- I tried v.split but don't know how to extract the nodes from the
resulting map.
- I also tried v.to.points but the distance is "random". Try this:

# NC data
v.to.points railroads output=railroads_nodes use=node dmax=200

g.region vector=railroads_nodes
d.mon wx0
d.vect railroads_nodes
--> ??

I found a hint about v.drape but also no success.

Any suggestions?

thanks
Markus

PS: I have roughly 100.000 lines to process.

2

Markus Neteler wrote

Hi devs,

I somehow don't get how to sample values from a raster map along a
vector line which is several pixels long.
In essence, something like this
#1852: r.profile: accept lines vector map as profile
https://trac.osgeo.org/grass/ticket/1852

Issues:
- I tried v.split but don't know how to extract the nodes from the
resulting map.
- I also tried v.to.points but the distance is "random". Try this:

# NC data
v.to.points railroads output=railroads_nodes use=node dmax=200

g.region vector=railroads_nodes
d.mon wx0
d.vect railroads_nodes
--> ??

I found a hint about v.drape but also no success.

Any suggestions?

thanks
Markus

PS: I have roughly 100.000 lines to process.
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a very simple implementation for just 1 vector line to get sample points
along a river/transect/whatever with a fixed segment length:

https://grass.osgeo.org/grass70/manuals/addons/v.fixed.segmentpoints.html

maybe it could be extended to loop through all lines of a vector?

-----
best regards
Helmut
--
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3

On 10/03/16 18:56, Markus Neteler wrote:

Hi devs,

I somehow don't get how to sample values from a raster map along a
vector line which is several pixels long.
In essence, something like this
#1852: r.profile: accept lines vector map as profile
https://trac.osgeo.org/grass/ticket/1852

Issues:
- I tried v.split but don't know how to extract the nodes from the
resulting map.
- I also tried v.to.points but the distance is "random". Try this:

# NC data
v.to.points railroads output=railroads_nodes use=node dmax=200

g.region vector=railroads_nodes
d.mon wx0
d.vect railroads_nodes
--> ??

This is the expected result with use=node. Try without that, and you should get what you are looking for:

v.to.points railroads output=railroads_nodes dmax=200

Moritz