v.what.vect(1grass) GRASS GIS User's Manual v.what.vect(1grass)
NAME
v.what.vect - Uploads vector values at positions of vector points to
the table.
KEYWORDS
vector, sampling, database, position, querying, attribute table
SYNOPSIS
v.what.vect
v.what.vect --help
v.what.vect map=name [layer=string] column=name query_map=name
[query_layer=string] query_column=name [dmax=float] [--help]
[--verbose] [--quiet] [--ui]
Flags:
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
map=name [required]
Name of vector points map for which to edit attributes
Or data source for direct OGR access
layer=string
Layer number or name
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
column=name [required]
Name of attribute column to be updated with the query result
query_map=name [required]
Name of vector map to be queried
Or data source for direct OGR access
query_layer=string
Layer number or name
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
query_column=name [required]
Name of attribute column to be queried
dmax=float
Maximum query distance in map units (meters for ll)
Default: 0.0
DESCRIPTION
v.what.vect transfers attributes from the query_map’s attribute table
into the map’s attribute table. The module can be used to transfer at-
tributes from the table of a polygon map into the attribute table of a
point vector map, as well as the other way around, i.e., from a point
map into the attribute table of a polygon map (See examples). The
script is based on v.distance.
NOTES
The upload column into which the query results are stored must be
present in map. Use v.db.addcolumn to add one if needed.
Use the dmax parameter to control the query distance tolerance, i.e.,
how far map’s points/centroids can be from the query_map features. For
further options, use v.distance.
In case of a multipoint input 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 query_map polygons.
When transferring attributes from a point map into a polygon map, dmax
has to be larger than zero, i.e., it will be determined by the distance
between query points and polygon centroids. Importantly, distance is in
meters for latitude-longitude locations.
In case that one or both input vector maps are 3D, features need to
touch also in the 3rd dimension (z coordinate) in order to transfer at-
tributes.
EXAMPLES
In this example, the ’hospitals’ point map in the North Carolina loca-
tion is copied to the current mapset, a new attribute column is added
and the urban names from the ’urbanarea’ polygon map are transferred to
hospital points locations in ’myhospitals’ map:
g.copy vect=hospitals,myhospitals
v.db.addcolumn myhospitals column="urb_name varchar(25)"
v.what.vect myhospitals query_map=urbanarea column=urb_name query_column=NAME
# verification:
v.db.select myhospitals
In this example, city names, population data and others from Geon-
ames.org country files are transferred to selected EU CORINE lan-
duse/landcover classes ("Continuous urban fabric", 111, and "Discontin-
uous urban fabric", 112). Note: The example is in UTM projection to
which the input maps have been projected beforehand.
# extract populated places from geonames
v.extract geonames_IT where="featurecla=’P’" output=geonames_IT_cities
# add new column
v.db.addcol corine_code111_112_cities column="gnameid double precision"
# transfer geonameid (3000m maximal distance between points and centroids)
v.what.vect corine_code111_112_cities query_map=geonames_IT_cities column=gnameid \
query_column=geonameid dmax=3000
# now gnameid can be used for v.db.join to join further
# attributes from geonames.org
SEE ALSO
v.db.addcolumn, v.db.select, v.distance, v.rast.stats, v.what.rast,
v.what.rast3, v.vect.stats
AUTHOR
Markus Neteler
SOURCE CODE
Available at: v.what.vect source code (history)
Accessed: unknown
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GRASS 7.8.7 v.what.vect(1grass)
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