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 (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 attributes 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 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 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 Geonames.org country files
       are transferred  to  selected  EU  CORINE  landuse/landcover  classes  ("Continuous  urban
       fabric",  111,  and  "Discontinuous  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)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual