[GRASS-dev] Re: [GRASS-user] points in polygon query
neteler at itc.it
Fri May 18 17:12:57 EDT 2007
Here a try but something is still missing:
# Task: count number of archaeological sites per field
# fetch field IDs:
v.category myfields layer=2 out=myfields2 op=add type=centroid
# prepare numer of points per polygon column:
v.db.addtable myfields2 layer=2 col="ptsnum integer"
v.info -c myfields2 layer=2
# prepare and fetch polygon numbers each archsite falls into:
v.db.addcol myarchsites col="polynum integer"
v.what.vect myarchsites qvector=myfields2 qcol=cat qlayer=2 col=polynum
d.vect myarchsites disp=shape,cat lcol=blue
# so far, so nice
# Approach 1:
v.what.vect myfields2 layer=2 col=ptsnum qvector=myarchsites qcol="count(polynum)"
# -> count() doesn't exist!
# Approach 2:
v.to.db myfields2 option=query layer=2 qlayer=1 [qvector=myarchsites] column=ptsnum qcolumn="count(*)"
# -> we cannot query the myarchsites here! qvector missing
Close but not yet. More ideas welcome...
On Fri, May 18, 2007 at 12:14:35PM -0400, M S wrote:
> cant you have a polygon coverage with an attribute in it "PolyNum" with
> unique IDs, and then do a v.overlay with the points and polys so the
> points get the PolyNum attribute?
> then run reports and summaries on the counts in each PolyNum. maybe I
> misunderstand the question.
> On 5/18/07, Markus Neteler <neteler at itc.it> wrote:
> someone asked me today a similar question as expressed by Maximiliano,
> no idea how to calculate this in an elegant way.
> Any suggestions how to count the number of points falling into polygons
> of another map?
> Massimiliano Cannata wrote:
> > Hi all,
> > I have a task to accomlpish but I don't know how to perform it...
> > Maybe someone can give me some hinits.... :-)
> > I have a points layer and a polygon layer.
> > I want to generate a map with the geometry of the polygons and an
> > attribute that is the count of the points that fall inside.
> > Example:
> > polygons: Municipalities
> > points: car accidents
> > resulting map: Municipalities represented for number of car accidents
> > Thanks you all,
> > Maxi
> > --
> > Dr. Eng. Massimiliano Cannata
> > Scuola Universitaria Professionale della Svizzera Italiana
> > Istituto Scienze della Terra
> > Via Trevano, c.p. 72
> > CH-6952 Canobbio-Lugano
> > Tel: +41 (0)58 666 62 14
> > Fax +41 (0)58 666 62 09
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Markus Neteler <neteler itc it> http://mpa.itc.it/markus/
FBK-irst - Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18 - 38050 Povo (Trento), Italy
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