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v.what.vect.1grass

NAME

v.what.vect - Uploads vector values at positions of vector points to the table.

KEYWORDS

vector, database, attribute table

SYNOPSIS

v.what.vect
v.what.vect help
v.what.vect vector=name [layer=integer] column=string qvector=name [qlayer=integer] qcolumn=string [dmax=float] [--verbose] [--quiet]

Parameters:

vector=name

Vector map to modify

layer=integer

Layer in the vector to be modified
Default: 1

column=string

Column to be updated with the query result

qvector=name

Vector map to be queried

qlayer=integer

Layer of the query vector containing data
Default: 1

qcolumn=string

Column to be queried

dmax=float

Maximum query distance in map units
Default: 0.0

DESCRIPTION

v.what.vect transfers attributes from the qvector's map attribute table into the attribute table of points present in the vector map. The script is based on v.distance.

NOTES

The upload column, into which the query results are stored, must be present in the vector map. Use v.db.addcol to add one if needed.

Use dmax parameter to control query distance tolerance (how far points/centroids can be from qvector features). For more options, use v.distance instead.

In case of a multipoint input vector map, with several points having the same category number, it can happen, that the query result is NULL, if the same category number falls into different qvector polygons.

When transferring attributes from a point map to a polygon map, usually dmax has to be larger than zero (determined by distance between query points and polygon centroids).

EXAMPLES

In this example, the 'archsites' point map in the Spearfish location is copied to the current mapset, a new attribute column is added and the owner names from the 'fields' polygon map are transferred to the 'myarchsites' map at points' locations:
g.copy vect=archsites,myarchsites
v.db.addcol myarchsites col="owner varchar(25)"
v.what.vect myarchsites qvect=fields column=owner qcolumn=label
# verification:
v.db.select myarchsites

In this example, city names, population data and more from Geonames.org country files are transferred to selected EU CORINE landuse/landcover classes ("Continuous urban fabric", 111, and "Discontinuous urban fabric", 112). Note: Example in UTM projection to which the input maps have been projected beforehand to have metric distances support:
# extract populated places from geonames
v.extract geonames_IT where="featurecla='P'" out=geonames_IT_cities
# add new column
v.db.addcol corine_code111_112_cities col="gnameid double precision"
# transfer geonameid (3000m maximal distance between points and centroids)
v.what.vect corine_code111_112_cities qvect=geonames_IT_cities col=gnameid \

            qcol=geonameid dmax=3000
# now gnameid can be used for v.db.join to join further
# attributes in from Geonames.org

SEE ALSO

v.db.addcol, v.db.select, v.distance, v.rast.stats, v.what.rast

AUTHOR

Markus Neteler

Last changed: $Date: 2009-11-29 11:12:00 +0100 (dom, 29 nov 2009) $

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