GRASS GIS manual: v.what.rast

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=string column=string [where=sql_query] [--verbose] [--quiet]

Parameters:

vector=name: Name of input vector map; Name of input vector points map for which to edit attribute table
raster=name: Name of existing raster map to be queried
layer=string: Layer number or name; A single vector map can be connected to multiple database tables. This number determines which table to use. Layer name for direct OGR access.; 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 < 1000 and inhab >= 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 column of 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:

v.db.connect -p vectpoints
# .. no table yet.

# add new table, link to map:
v.db.addtable vectpoints col="cat integer, myvalue integer, otherval double precision"

# query raster map and upload values to vector table into specified column:
v.what.rast vect=vectpoints rast=rastmap col=myvalue

# verify new attribute table:
v.db.select vectpoints

# verify statistics of uploaded values:
v.univar map=vectpoints col=myvalue type=point

AUTHOR

Radim Blazek

Last changed: $Date: 2008-08-14 23:16:42 -0700 (Thu, 14 Aug 2008) $

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