[GRASS-user] points in polygon query

Hamish hamish_nospam at yahoo.com
Mon May 21 03:39:38 EDT 2007

Stefano Costa wrote:
> Scrive Dylan Beaudette <dylan.beaudette at gmail.com>:
> > This sounds like a form of quadrat counting
> Last night I wrote this script that does the job. Quite slow, but
> works. http://grass.gdf-hannover.de/wiki/V.count.points

re speed-

> echo "UPDATE $output SET count = $count WHERE cat = $i" | db.execute

instead of running db.execute at every iteration in your loop, >> append
the SQL command to a g.tempfile (end each line with a ';'), then once
the for loops are done, run db.execute once with the input=$tempfile.

then the script will be much much faster I think.

> for i in $areas; do
>    count=$( db.select -c points_tmp sql="select cat_area from points_tmp" | grep -c $i)

You might want to make the ending "grep -c $i" a bit more specific,
as you don't want to count "10,11,Site 1" in a where="cat = 1" grep count.
As written it could lead to buggy results.

for example:
G63> g.copy v=bugsites,local_bugs
G63> i=1
G63> db.select local_bugs | grep -c $i
G63> db.select local_bugs | grep -c "^$i|"

also if you save the output of db.select to a temp file you don't need
to run the process for every step in the loop, as it doesn't change.
Maybe a bit faster that way- move as much repeated static operations
as possible out of loops.


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