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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 access 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 access 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
           Default: 0.0

DESCRIPTION

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

NOTES

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

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

       In  case  of  a  multipoint  input  map  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 to a polygon map, usually dmax has to be
       larger than zero (determined by distance between query points and polygon centroids).

       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 attributes.

EXAMPLES

       In this example, the ’hospitals’ point map in the North Carolina location is copied to the
       current mapset, a new attribute column is added and the urban names from  the  ’urbanarea’
       polygon map are transferred to the ’myhospitals’ map at the hospital points’ locations:
       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 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’" 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 in from geonames.org

SEE ALSO

        v.db.addcolumn, v.db.select, v.distance, v.rast.stats, v.what.rast, v.what.rast3

AUTHOR

       Markus Neteler

       Last changed: $Date: 2015-10-07 10:15:43 +0200 (Wed, 07 Oct 2015) $

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