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v.extract

Langue: en

Autres versions - même langue

Version: 369738 (fedora - 01/12/10)

Section: 1 (Commandes utilisateur)

NAME

v.extract - Selects vector objects from an existing vector map and creates a new map containing only the selected objects.
If 'list', 'file' and 'where' options are not specified, all features of given type and layer are extracted. Categories are not changed in that case.

KEYWORDS

vector

SYNOPSIS

v.extract
v.extract help
v.extract [-dtr] input=name output=name [type=string[,string,...]] [layer=integer] [new=integer] [list=range] [file=name] [where=sql_query] [--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,...]

Type
Types to be extracted
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
Default: 1
new=integer

Enter -1 to keep original categories or the desired NEW category value
If new >= 0, table is not copied
Default: -1
list=range

Category values
Example: 1,3,7-9,13
file=name

Input text file with category numbers/number ranges to be extracted
If '-' given reads from standard input
where=sql_query

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

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.

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

Extract areas by category number with dissolving #1:


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.

Extract areas by category number with dissolving #2:


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.

Extract vectors with SQL:


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.

Extract vector features which have the given field empty:


v.extract input=forest output=forest_gaps where="CANOPY is NULL"

Extract vector features which have the given field not empty:


v.extract input=forest output=forest_canopy where="CANOPY not NULL"

Reverse extracting (behaves like selective vector objects deleting):

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

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: 2007-05-17 11:08:04 +0200 (Thu, 17 May 2007) $

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© 2003-2008 GRASS Development Team

Ici, l'exemple est un peu capillotracté.
Si on choisissait plutôt un dilemme entre fr.comp.os.unix et
fr.rec.arts.os.unix ?
-+- APM in: Guide du Cabaliste Usenet - La Cabale est-elle barbue ? -+-