[GRASS-user] clipping line data to a polygon

GRASS GRASS user
1

Is the best way to clip data to use the v.overlay command with the “and” operator?

it works great, but seems quite slow on larger datasets. Additionally as an example, if i have topographic contour lines, and i want to clip them to a polygon, and only want the topo line attributes (elevation) outputted, is there a way to do this? Is there another way to clip line data to within a polygon that might be a bit faster?

thanks,
Mark

2

Mark wrote:

Is the best way to clip data to use the v.overlay command with the "and"
operator?

it works great, but seems quite slow on larger datasets. Additionally as an
example, if i have topographic contour lines, and i want to clip them to a
polygon, and only want the topo line attributes (elevation) outputted, is
there a way to do this? Is there another way to clip line data to within a
polygon that might be a bit faster?

run v.select, then v.overlay. That way the intensive v.overlay operation only
happens for relevant vector features. Then it will speed up hugely.

I wonder if v.select functionality could be built into v.overlay as a
preprocessing step?

Hamish

____________________________________________________________________________________
Moody friends. Drama queens. Your life? Nope! - their life, your story. Play Sims Stories at Yahoo! Games.
http://sims.yahoo.com/

3

Mark wrote:
> Is the best way to clip data to use the v.overlay command with the
> "and" operator?
>
> it works great, but seems quite slow on larger datasets.
> Additionally as an example, if i have topographic contour lines, and
> i want to clip them to a polygon, and only want the topo line
> attributes (elevation) outputted, is there a way to do this? Is
> there another way to clip line data to within a polygon that might
> be a bit faster?

Hamish:

run v.select, then v.overlay. That way the intensive v.overlay
operation only happens for relevant vector features. Then it will
speed up hugely.

I wonder if v.select functionality could be built into v.overlay as a
preprocessing step?

(see Radim's doc/vector/TODO in the source code; maybe splitting long
boundaries helps too?)

Hamish

4

Sorry if my answer is a bit out of the scope of Grass :
from time to time I use OpenJump GIS. For this type of task (don't ask
me why) it's incredibly faster. Maybe any of you could explain this
difference ?

VB

Le vendredi 17 août 2007 à 17:21 +1200, Hamish a écrit :

> Mark wrote:
> > Is the best way to clip data to use the v.overlay command with the
> > "and" operator?
> >
> > it works great, but seems quite slow on larger datasets.
> > Additionally as an example, if i have topographic contour lines, and
> > i want to clip them to a polygon, and only want the topo line
> > attributes (elevation) outputted, is there a way to do this? Is
> > there another way to clip line data to within a polygon that might
> > be a bit faster?
>
Hamish:
> run v.select, then v.overlay. That way the intensive v.overlay
> operation only happens for relevant vector features. Then it will
> speed up hugely.
>
> I wonder if v.select functionality could be built into v.overlay as a
> preprocessing step?

(see Radim's doc/vector/TODO in the source code; maybe splitting long
boundaries helps too?)

Hamish

_______________________________________________
grassuser mailing list
grassuser@grass.itc.it
http://grass.itc.it/mailman/listinfo/grassuser