[GRASS-dev] Re: [GRASS-user] points in polygon query

[Markus Neteler]

Here a try but something is still missing:

# Spearfish
# Task: count number of archaeological sites per field

g.copy vect=fields,myfields
# 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

g.copy vect=archsites,myarchsites
# 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
v.db.select myarchsites

# 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...
Markus

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.
> 
>    Mark
> 
>    On 5/18/07, Markus Neteler <[1]neteler at itc.it> wrote:
> 
>      Hi,
> 
>      someone asked me today a similar question as expressed by Maximiliano,
>      still
>      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?
> 
>      Markus
> 
>      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