NAME

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

KEYWORDS

       vector, raster, attribute table

SYNOPSIS

       v.what.rast
       v.what.rast help
       v.what.rast  vector=name  raster=name   [layer=integer]   column=string  [where=sql_query]
       [--verbose]  [--quiet]

   Parameters:
       vector=name
           Name of input vector points map for which to edit attribute table

       raster=name
           Name of existing raster map to be queried

       layer=integer
           Layer number
           A single vector map  can  be  connected  to  multiple  database  tables.  This  number
           determines which table to use.
           Default: 1

       column=string
           Column name (will be updated by raster values)

       where=sql_query
           WHERE conditions of SQL statement without 'where' keyword
           Example: income = 10000

DESCRIPTION

       v.what.rast  reads  raster  value  for  each point in the vector and updates col column in
       vector attribute table by this value. The column should be type  number  (integer,  float,
       double, ... ).
       If  more  points have the same category, attribute value is set to NULL.  If raster values
       is NULL, attribute value is set to NULL.

NOTES

       v.what.rast operates on the attribute table. To modify the vector  geometry  instead,  use
       v.drape.

EXAMPLES

       A)  Reading values from raster map at position of vector points, writing these values into
       a column of the attribute table connected to the vector map:

       v.what.rast vect=pnts rast=elevation col=heights

       B) In case of a vector map without attached attribute table, first  add  a  new  attribute
       table. This table is then populated with values queried from the raster map:

       # create new random vector points map
       v.random pnts n=100
       # add new table, link to map
       v.db.addtable pnts col="heights double precision"
       # query raster map and upload values to vector table into specified column
       g.region rast=elevation -p
       v.what.rast vect=pnts raster=elevation column=heights
       # verify new attribute table:
       v.db.select pnts
       # verify statistics of uploaded values:
       v.univar map=pnts column=heights type=point

SEE ALSO

        v.db.addtable, v.db.select, v.drape, v.univar, v.rast.stats, v.what.vect

AUTHOR

       Radim Blazek

       Last changed: $Date: 2012-02-08 13:39:58 -0800 (Wed, 08 Feb 2012) $

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