[GRASS-user] v.overlay: An Observation About Time

GRASS GRASS user
1

   I have a map of water bodies for the entire state. Yesterday, when I
re-imported it (correctly), it took about 3 hours to complete; most of the
time was waiting for it to 'break boundaries'.

   Today I'm clipping it to a very small region, one drainage basin and parts
of the surrounding basins, yet it's taking about the same amount of time.
Yes, there are a lot of nodes, vertices, and primitives, but I want only
those within the area of the overlaid map. So I'm surprised it's taking as
long as it is.

   This is an extensive original map:

Building topology for vector map <bl_lakes>...
Registering primitives...
220819 primitives registered
4589198 vertices registered
Number of nodes: 158848
Number of primitives: 220819
Number of points: 0
Number of lines: 0
Number of boundaries: 220819
Number of centroids: 0
Number of areas: -
Number of isles: -
Breaking lines...
Removing duplicates...
Cleaning boundaries at nodes...
Breaking lines...

   This is not a complaint, but an observation.

Rich

2

v.select can be a nice first pass to filter back a substantial amount of unnecessary data.

Mark

On Dec 30, 2009, at 2:33 PM, Rich Shepard <rshepard@appl-ecosys.com> wrote:

I have a map of water bodies for the entire state. Yesterday, when I
re-imported it (correctly), it took about 3 hours to complete; most of the
time was waiting for it to 'break boundaries'.

Today I'm clipping it to a very small region, one drainage basin and parts
of the surrounding basins, yet it's taking about the same amount of time.
Yes, there are a lot of nodes, vertices, and primitives, but I want only
those within the area of the overlaid map. So I'm surprised it's taking as
long as it is.

This is an extensive original map:

Building topology for vector map <bl_lakes>...
Registering primitives...
220819 primitives registered
4589198 vertices registered
Number of nodes: 158848
Number of primitives: 220819
Number of points: 0
Number of lines: 0
Number of boundaries: 220819
Number of centroids: 0
Number of areas: -
Number of isles: -
Breaking lines...
Removing duplicates...
Cleaning boundaries at nodes...
Breaking lines...

This is not a complaint, but an observation.

Rich
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3

On Wed, 30 Dec 2009, MS wrote:

v.select can be a nice first pass to filter back a substantial amount of
unnecessary data.

Mark,

   Thank you. I'll keep this in mind for future clipping.

Rich

4

Rich wrote:

I have a map of water bodies
for the entire state. Yesterday, when I
re-imported it (correctly), it took about 3 hours to
complete; most of the
time was waiting for it to 'break boundaries'.

fyi this is the classic "Florida Coastline" problem.
to work around it, after it is in grass you can use the v.split
command on it, after that it will be faster. (if may is really
huge it may still take some time..)
see the mailing list archives.

Hamish