v.extract(1)

1v.extract(1)                  Grass User's Manual                 v.extract(1)
2
3
4

NAME

6       v.extract   -  Selects  vector  objects from an existing vector map and
7       creates a new map containing only the selected objects.
8       If 'list', 'file' and 'where' options are not specified,  all  features
9       of  given  type  and layer are extracted. Categories are not changed in
10       that case.
11

KEYWORDS

13       vector
14

SYNOPSIS

16       v.extract
17       v.extract help
18       v.extract  [-dtr]  input=name  output=name   [type=string[,string,...]]
19       [layer=integer]       [new=integer]       [list=range]      [file=name]
20       [where=sql_query]   [--overwrite]  [--verbose]  [--quiet]
21
22   Flags:
23       -d
24           Dissolve common boundaries (default is no)
25
26       -t
27           Do not copy table (see also 'new' parameter)
28
29       -r
30           Reverse selection
31
32       --overwrite
33           Allow output files to overwrite existing files
34
35       --verbose
36           Verbose module output
37
38       --quiet
39           Quiet module output
40
41   Parameters:
42       input=name
43           Name of input vector map
44
45       output=name
46           Name for output vector map
47
48       type=string[,string,...]
49           Type
50           Types to be extracted
51           Options: point,line,boundary,centroid,area,face
52           Default: point,line,boundary,centroid,area,face
53
54       layer=integer
55           Layer number
56           If -1, all features in all layers of given type are extracted
57           Default: 1
58
59       new=integer
60           Enter -1 to keep original categories or the  desired  NEW  category
61           value
62           If new >= 0, table is not copied
63           Default: -1
64
65       list=range
66           Category values
67           Example: 1,3,7-9,13
68
69       file=name
70           Input text file with category numbers/number ranges to be extracted
71           If '-' given reads from standard input
72
73       where=sql_query
74           WHERE conditions of SQL statement without 'where' keyword
75           Example: income = 10000
76

DESCRIPTION

78       v.extract  allows a user to select vector objects from an existing vec‐
79       tor map and creates a new map containing  only  the  selected  objects.
80       Database  tables can be queried with SQL statements, if a connection is
81       established.  Dissolving (optional) is based on the output  categories.
82       If  2  adjacent  areas  have  the same output category, the boundary is
83       removed.
84

NOTES

86       Only features with a category number will be extracted. So if you  want
87       to  extract  boundaries  (which  are  usually without category, as that
88       information is normally held in the area's centroid) you must first use
89       v.category to add them.
90

EXAMPLES

92   Extract areas by category number with dissolving #1:
93
94       v.extract  -d  list=1,2,3,4  input=soils  output=soil_groupa  type=area
95       new=0
96
97
98       produces a new vector soil_groupa, containing those areas  from  vector
99       soils  which  have category numbers 1 thru 4; any common boundaries are
100       dissolved, and all areas in the new map will be assigned category  num‐
101       ber 0.
102
103   Extract areas by category number with dissolving #2:
104
105       v.extract -d list=1-4 input=soils output=soil_groupa type=area new=-1
106
107
108       produces  a new vector map soil_groupa containing the areas from vector
109       soils which have categories 1 thru 4. Any common  boundaries  are  dis‐
110       solved,  all  areas  in the new map will retain their original category
111       numbers 1 thru 4, since new was set to -1.
112
113   Extract all areas and assign the same category to all:
114
115       v.extract input=soils output=soil_groupa type=area new=1
116
117
118       produces a new vector map soil_groupa containing all areas from  soils.
119       No  common  boundaries  are dissolved, all areas of the new map will be
120       assigned category number 1.
121
122   Extract vectors with SQL:
123
124       v.extract input=markveggy.shp output=markveggy.1 new=13 where="(VEGTYPE
125       = 'Wi') or (VEGTYPE = 'PS') or (PRIME_TYPE='Wi')"
126
127
128       produces  a new vector map with category number 13 if the SQL statement
129       is fulfilled.
130
131   Extract vector features which have the given field empty:
132
133       v.extract input=forest output=forest_gaps where="CANOPY is NULL"
134
135
136   Extract vector features which have the given field not empty:
137
138       v.extract input=forest output=forest_canopy where="CANOPY not NULL"
139
140
141   Reverse extracting (behaves like selective vector objects deleting):
142       Remove unreferenced stations from the GlobalSOD database:
143       # check what to delete:
144       v.db.select gsod_stationlist where="latitude < -91"
145       # perform reverse selection
146       v.extract -r gsod_stationlist  out=gsod_stationlist_clean  where="lati‐
147       tude < -91"
148       v.db.select gsod_stationlist_clean
149
150
151   Dissolving based on column attributes:
152
153       # check column names:
154       v.info -c polbnda_italy
155       # reclass based on desired column:
156       v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam
157       # verify:
158       v.info -c polbnda_italy_recl_nam
159       v.db.select polbnda_italy_recl_nam
160       # dissolve:
161       v.extract -d polbnda_italy_recl_nam out=pol_italy_regions
162
163
164       produces  a  new  vector map with common boundaries dissolved where the
165       reclassed attributes of adjacent (left/right) areas are identical.
166
167   Remove islands from polygon map
168
169       v.extract in=map_with_islands out=maps_without_islands list=1-99999
170       # and/or
171       v.extract -d in=map_with_islands out=maps_without_islands
172
173

AUTHORS

178       R.L. Glenn, USDA, SCS, NHQ-CGIS
179       GRASS 6 port by Radim Blazek
180
181       Last changed: $Date: 2007-05-17 11:08:04 +0200 (Thu, 17 May 2007) $
182
183       Full index
184
185       © 2003-2008 GRASS Development Team
186
187
188
189GRASS 6.3.0                                                       v.extract(1)