NAME¶
v.extract - Selects vector objects from an existing vector map and
creates a new map containing only the selected objects.
KEYWORDS¶
vector, extract
SYNOPSIS¶
v.extract
v.extract help
v.extract [-
dtr]
input=
name
output=
name [
type=
string[,
string,...]]
[
layer=
integer] [
list=
range]
[
where=
sql_query] [
file=
name]
[
random=
integer] [
new=
integer]
[--
overwrite] [--
verbose] [--
quiet]
Flags:¶
- -d
-
Dissolve common boundaries (default is no)
- -t
-
Do not copy table (see also 'new' parameter)
- -r
-
Reverse selection
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- input=name
-
Name of input vector map
- output=name
-
Name for output vector map
- type=string[,string,...]
-
Types to be extracted
Feature type
Options: point,line,boundary,centroid,area,face
Default: point,line,boundary,centroid,area,face
- layer=integer
-
Layer number (if -1, all features in all layers of given type are extracted)
A single vector map can be connected to multiple database tables. This
number determines which table to use.
Default: 1
- list=range
-
Category values
Example: 1,3,7-9,13
- where=sql_query
-
WHERE conditions of SQL statement without 'where' keyword
Example: income = 10000
- file=name
-
Input text file with category numbers/number ranges to be extracted
If '-' given reads from standard input
- random=integer
-
Number of random categories matching vector objects to extract
Number must be smaller than unique cat count in layer
- new=integer
-
Enter -1 to keep original categories or the desired NEW category value
If new >= 0, table is not copied
Default: -1
DESCRIPTION¶
v.extract allows a user to select vector objects from an existing vector
map and creates a new map containing only the selected objects. Database
tables can be queried with SQL statements, if a connection is established.
Dissolving (optional) is based on the output categories. If 2 adjacent areas
have the same output category, the boundary is removed.
If
list,
file,
random or
where options are not
specified, all features of given type and layer are extracted. Categories are
not changed in that case.
NOTES¶
Only features with a category number will be extracted. So if you want to
extract boundaries (which are usually without category, as that information is
normally held in the area's centroid) you must first use
v.category to
add them.
EXAMPLES¶
v.extract -d list=1,2,3,4 input=soils output=soil_groupa type=area new=0
produces a new vector
soil_groupa, containing those areas from vector
soils which have category numbers
1 thru 4; any common
boundaries are dissolved, and all areas in the new map will be assigned
category number 0.
v.extract -d list=1-4 input=soils output=soil_groupa type=area new=-1
produces a new vector map
soil_groupa containing the areas from vector
soils which have categories
1 thru 4. Any common boundaries are
dissolved, all areas in the new map will retain their original category
numbers 1 thru 4, since
new was set to -1.
Extract all areas and assign the same category to all:¶
v.extract input=soils output=soil_groupa type=area new=1
produces a new vector map
soil_groupa containing all areas from
soils. No common boundaries are dissolved, all areas of the new map
will be assigned category number 1.
v.extract input=markveggy.shp output=markveggy.1 new=13 where="(VEGTYPE =
'Wi') or (VEGTYPE = 'PS') or (PRIME_TYPE='Wi')"
produces a new vector map with category number 13 if the SQL statement is
fulfilled.
v.extract input=forest output=forest_gaps where="CANOPY is NULL"
v.extract input=forest output=forest_canopy where="CANOPY not NULL"
Remove unreferenced stations from the GlobalSOD database:
# check what to delete:
v.db.select gsod_stationlist where="latitude < -91"
# perform reverse selection
v.extract -r gsod_stationlist out=gsod_stationlist_clean where="latitude
< -91"
v.db.select gsod_stationlist_clean
Dissolving based on column attributes:¶
# check column names:
v.info -c polbnda_italy
# reclass based on desired column:
v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam
# verify:
v.info -c polbnda_italy_recl_nam
v.db.select polbnda_italy_recl_nam
# dissolve:
v.extract -d polbnda_italy_recl_nam out=pol_italy_regions
produces a new vector map with common boundaries dissolved where the reclassed
attributes of adjacent (left/right) areas are identical.
Remove islands from polygon map¶
v.extract in=map_with_islands out=maps_without_islands list=1-99999
# and/or
v.extract -d in=map_with_islands out=maps_without_islands
Extract 3 random areas from geology map¶
v.extract input=geology output=random_geology type=area random=3
will create new map with three random categories matching areas. Note that there
may be more than one feature with the same category.
SEE ALSO¶
v.category, v.dissolve, v.reclass, GRASS SQL
interface
AUTHORS¶
R.L. Glenn, USDA, SCS, NHQ-CGIS
GRASS 6 port by Radim Blazek
Last changed: $Date: 2011-11-08 10:42:51 +0100 (Tue, 08 Nov 2011) $
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