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NAME

v.select - Selects features from vector map (A) by features from other vector map (B).

KEYWORDS

vector, spatial query

SYNOPSIS

v.select
v.select help
v.select [-tcr] ainput=name [atype=string[,string,...]] [alayer=integer] binput=name [btype=string[,string,...]] [blayer=integer] output=name [operator=string] [--overwrite] [--verbose] [--quiet]

Flags:

-t
Do not create attribute table
-c
Do not skip features without category
-r
Reverse selection
--overwrite
Allow output files to overwrite existing files
--verbose
Verbose module output
--quiet
Quiet module output

Parameters:

ainput=name
Name of input vector map (A)
atype=string[,string,...]
Feature type (vector map A)
Feature type
Options: point,line,boundary,centroid,area
Default: point,line,boundary,centroid,area
alayer=integer
Layer number (vector map A)
A single vector map can be connected to multiple database tables. This number determines which table to use.
Default: 1
binput=name
Name of input vector map (B)
btype=string[,string,...]
Feature type (vector map B)
Feature type
Options: point,line,boundary,centroid,area
Default: point,line,boundary,centroid,area
blayer=integer
Layer number (vector map B)
A single vector map can be connected to multiple database tables. This number determines which table to use.
Default: 1
output=name
Name for output vector map
operator=string
Operator defines required relation between features
A feature is written to output if the result of operation 'ainput operator binput' is true. An input feature is considered to be true, if category of given layer is defined.
Options: overlap
Default: overlap
overlap: features partially or completely overlap

DESCRIPTION

v.select allows the user to select features from a vector map by features from another one.

Supported operators (without GEOS):

Supported operators (with GEOS):

NOTES

Only features with category numbers will be considered. If required the v.category module can be used to add them. Typically boundaries do not need to be given a category number, as an area's attributes are inherited from the centroid. Typically points, lines, and centroids will always want to have a cat number.

E.g. take a road which separates two farms. It is ambiguous as to which farm an attribute that is attached to the road belongs to. The boundary only needs a cat number if it will hold its own attributes, such as road name or pavement form. A centroid in each paddock holds the information with respect to ownership, area, etc.

EXAMPLES

Extract forest fire points from larger fire vector map:
v.select ainput=fire binput=forest output=forest_fire operator=overlap
Extract Italian rivers from VMAP0 watercourses map:
v.select ainput=watrcrsl_eurnasia_wgs84 binput=italy_area \
         output=watrcrsl_italy operator=overlap

TODO

Processing areas with GEOS is currently incredibly slow. Significant speed-up is required.

SEE ALSO

v.category, v.overlay

GRASS SQL interface

AUTHORS

Radim Blazek
Updated by Martin Landa, CTU in Prague, Czech Republic (GEOS support)

Last changed: $Date: 2010-11-07 09:37:50 -0800 (Sun, 07 Nov 2010) $


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