v.extract(1)

1v.extract(1)                  Grass User's Manual                 v.extract(1)
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NAME

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

KEYWORDS

12       vector
13

SYNOPSIS

15       v.extract
16       v.extract help
17       v.extract  [-dt]  input=name  output=name    [type=string[,string,...]]
18       [layer=integer]          [new=integer]         [list=range[,range,...]]
19       [file=string]   [where=sql_query]   [--overwrite]
20
21   Flags:
22       -d  Dissolve common boundaries (default is no)
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24       -t  Do not copy table (see also 'new' parameter)
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26       --overwrite
27
28   Parameters:
29       input=name
30           Name of input vector map
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32       output=name
33           Name for output vector map
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35       type=string[,string,...]
36           Types   to   be   extracted    Options:    point,line,boundary,cen‐
37           troid,area,face Default: point,line,boundary,centroid,area,face
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39       layer=integer
40           Layer  number.  If -1, all features in all layers of given type are
41           extracted.  Default: 1
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43       new=integer
44           Enter -1 to keep original categories or the  desired  NEW  category
45           value. If new >= 0, table is not copied.  Default: -1
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47       list=range[,range,...]
48           Category ranges: e.g. 1,3-8,13
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50       file=string
51           Input text file with category numbers/number ranges to be extracted
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53       where=sql_query
54           WHERE  conditions  of SQL statement without 'where' keyword. (exam‐
55           ple: income = 10000)
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DESCRIPTION

58       v.extract allows a user to select vector objects from an existing  vec‐
59       tor  map  and  creates  a new map containing only the selected objects.
60       Database tables can be queried with SQL statements, if a connection  is
61       established.   Dissolving (optional) is based on the output categories.
62       If 2 adjacent areas have the same  output  category,  the  boundary  is
63       removed.
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NOTES

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

72   Extract areas by category number with dissolving #1:
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74       v.extract  -d  list=1,2,3,4  input=soils  output=soil_groupa  type=area
75       new=0
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78       produces  a  new vector soil_groupa, containing those areas from vector
79       soils which have category numbers 1 thru 4; any common  boundaries  are
80       dissolved,  and all areas in the new map will be assigned category num‐
81       ber 0.
82
83   Extract areas by category number with dissolving #2:
84
85       v.extract -d list=1-4 input=soils output=soil_groupa type=area new=-1
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87
88       produces a new vector map soil_groupa containing the areas from  vector
89       soils  which  have  categories 1 thru 4. Any common boundaries are dis‐
90       solved, all areas in the new map will retain  their  original  category
91       numbers 1 thru 4, since new was set to -1.
92
93   Extract all areas and assign the same category to all:
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95       v.extract input=soils output=soil_groupa type=area new=1
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97
98       produces  a new vector map soil_groupa containing all areas from soils.
99       No common boundaries are dissolved, all areas of the new  map  will  be
100       assigned category number 1.
101
102   Extract vectors with SQL:
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104       v.extract input=markveggy.shp output=markveggy.1 new=13 where="(VEGTYPE
105       = 'Wi') or (VEGTYPE = 'PS') or (PRIME_TYPE='Wi')"
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107
108       produces a new vector map with category number 13 if the SQL  statement
109       is fulfilled.
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111   Extract vector features which have the given field empty:
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113       v.extract input=forest output=forest_gaps where="CANOPY is NULL"
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115
116   Extract vector features which have the given field not empty:
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118       v.extract input=forest output=forest_canopy where="CANOPY not NULL"
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120
121   Dissolving based on column attributes:
122
123       # check column names:
124       v.info -c polbnda_italy
125       # reclass based on desired column:
126       v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam
127       # verify:
128       v.info -c polbnda_italy_recl_nam
129       v.db.select polbnda_italy_recl_nam
130       # dissolve:
131       v.extract -d polbnda_italy_recl_nam out=pol_italy_regions
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133
134       produces  a  new  vector map with common boundaries dissolved where the
135       reclassed attributes of adjacent (left/right) areas are identical.
136
137   Remove islands from polygon map
138
139       v.extract in=map_with_islands out=maps_without_islands list=1-99999
140       # and/or
141       v.extract -d in=map_with_islands out=maps_without_islands
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AUTHOR

148       R.L. Glenn, USDA, SCS, NHQ-CGIS
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150       Last changed: $Date: 2006/10/31 19:16:26 $
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152       Full index
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156GRASS 6.2.2                                                       v.extract(1)