[GRASS-user] Clipping Very Large Vector Map

GRASS GRASS user
1

   I have a map of streams and rivers that is about 474M for the coor file
and 65M for the topo file; very large. The area of interest is very much
smaller and I tried using v.overlay with the 'and' (intersect) operator to
clip the huge line map with the small area map. After about 1/2-hour of
processing the system shut down because the CPU overheated (at it's only 20C
here today).

   Are there other modules, or ways of using v.overlay, that will allow me to
trim off smaller chunks of the line file?

TIA,

Rich

2

maybe gdalwarp can do it? it has a clipping option where you give coordinates of a rectangle.

best

Carlos

On Mon, Oct 8, 2012 at 8:28 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:

I have a map of streams and rivers that is about 474M for the coor file
and 65M for the topo file; very large. The area of interest is very much
smaller and I tried using v.overlay with the ‘and’ (intersect) operator to
clip the huge line map with the small area map. After about 1/2-hour of
processing the system shut down because the CPU overheated (at it’s only 20C
here today).

Are there other modules, or ways of using v.overlay, that will allow me to
trim off smaller chunks of the line file?

TIA,

Rich

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3

On Mon, 8 Oct 2012, Carlos Grohmann wrote:

maybe gdalwarp can do it? it has a clipping option where you give
coordinates of a rectangle.

Carlos,

   The clip box is not quite rectangular. In any case, I think it is the huge
size of the line map on a system with "only" 4G of memory that might be the
problem.

   Looking at v.select suggests that it might work, but I've no way of
knowing if it is any more efficient than v.overlay, and I don't want to
re-boot my server/workstation again. :slight_smile:

Thanks,

Rich

4

On Mon, 8 Oct 2012, Rich Shepard wrote:

Are there other modules, or ways of using v.overlay, that will allow me
to trim off smaller chunks of the line file?

   If I create a new map of a box that is slightly smaller in are than the
large stream/river map, and use the 'not' operator with v.overlay, will this
be a quicker way of trimming off the lines external to the new box?

   If so, I can keep creating new boxes, each smaller than the last, and clip
the line map in smaller bites.

Rich

5

On Mon, 8 Oct 2012, Rich Shepard wrote:

If I create a new map of a box that is slightly smaller in are than the

                                                               ^^^
   area

6

try using v.select.

Rich Shepard rshepard@appl-ecosys.com escribió:

   I have a map of streams and rivers that is about 474M for the coor file
and 65M for the topo file; very large. The area of interest is very much
smaller and I tried using v.overlay with the 'and' (intersect) operator to
clip the huge line map with the small area map. After about 1/2-hour of
processing the system shut down because the CPU overheated (at it's only 20C
here today).

Are there other modules, or ways of using v.overlay, that will allow me to
trim off smaller chunks of the line file?

TIA,

Rich

---

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7

On Tue, 9 Oct 2012, Juan Carlos Torrrs wrote:

try using v.select.

Juan,

   That was one of my thoughts, and it did the job when I properly specified
the a and b maps.

   Thanks for the suggestion.

Rich