[GRASS-user] making an area with existing lines

GRASS GRASS user
1

Hello,
I have two vector lines and I want to limit operations to the the area in
between these lines. I've had some ideas about how to do this, but I really
don't know how to. I don't know if this extra info would be useful, but here
it is: the lines are a road and a shoreline, the are roughly parallel, and
they do not cross. At first I thought maybe I could export them as ascii,
concatenate the list and import as an area, then convert to a raster that I
could use as a mask. I don't actually know if this would work because I was
having some troubles exporting the vector files, they were blank. But
anyway, if anyone could let me know what they think, that would be great.
Thanks,
Eric
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2

hardinej wrote:

Hello,
I have two vector lines and I want to limit operations to the the area in
between these lines. I've had some ideas about how to do this, but I really
don't know how to. I don't know if this extra info would be useful, but here
it is: the lines are a road and a shoreline, the are roughly parallel, and
they do not cross. At first I thought maybe I could export them as ascii,
concatenate the list and import as an area, then convert to a raster that I
could use as a mask. I don't actually know if this would work because I was
having some troubles exporting the vector files, they were blank. But
anyway, if anyone could let me know what they think, that would be great. Thanks,
Eric
  

Depends on what operations you're planning. vector? or raster?
For raster, I'd make the two parallel lines into a closed boundary (using v.digit) and also digitize a centroid. THen I'd change the vector area to a raster (v.to.rast type=area ...) and finally use that raster as a mask. Now all raster operations will be limited to the area between the two lines.
If it's vector operations, I'd guess that you'll again want to create a closed boundary with a centroid, and then, after running whatever operations you have in mind, just do "v.overlay operator=and ..." to get results again only in between the parallel lines.
--
Micha

3

Micha Silver wrote:

hardinej wrote:

Hello,
I have two vector lines and I want to limit operations to the the area in
between these lines. I've had some ideas about how to do this, but I really
don't know how to. I don't know if this extra info would be useful, but here
it is: the lines are a road and a shoreline, the are roughly parallel, and
they do not cross. At first I thought maybe I could export them as ascii,
concatenate the list and import as an area, then convert to a raster that I
could use as a mask. I don't actually know if this would work because I was
having some troubles exporting the vector files, they were blank. But
anyway, if anyone could let me know what they think, that would be great. Thanks,
Eric

Depends on what operations you're planning. vector? or raster?
For raster, I'd make the two parallel lines into a closed boundary (using v.digit) and also digitize a centroid. THen I'd change the vector area to a raster (v.to.rast type=area ...) and finally use that raster as a mask. Now all raster operations will be limited to the area between the two lines.
If it's vector operations, I'd guess that you'll again want to create a closed boundary with a centroid, and then, after running whatever operations you have in mind, just do "v.overlay operator=and ..." to get results again only in between the parallel lines.

Or run v.select first to select only the features falling into the newly created area. That may be faster, depending on the subsequent vector operation.

4

Thanks Micha
I'll have to get used to learn to use v.digit.
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