1v.extract(1) GRASS GIS User's Manual v.extract(1)
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6 v.extract - Selects vector features from an existing vector map and
7 creates a new vector map containing only the selected features.
8
10 vector, extract, select, dissolve, random
11
13 v.extract
14 v.extract --help
15 v.extract [-dtr] input=name [layer=string]
16 [type=string[,string,...]] [cats=range] [where=sql_query] out‐
17 put=name [file=name] [random=integer] [new=integer] [dis‐
18 solve_column=name] [--overwrite] [--help] [--verbose] [--quiet]
19 [--ui]
20 Flags:
22 -d
23 Dissolve common boundaries (default is no)
24 -t
26 Do not copy attributes (see also ’new’ parameter)
27 -r
29 Reverse selection
30 --overwrite
32 Allow output files to overwrite existing files
33 --help
35 Print usage summary
36 --verbose
38 Verbose module output
39 --quiet
41 Quiet module output
42 --ui
44 Force launching GUI dialog
45 Parameters:
47 input=name [required]
48 Name of input vector map
49 Or data source for direct OGR access
50 layer=string
52 Layer number or name (’-1’ for all layers)
53 A single vector map can be connected to multiple database tables.
54 This number determines which table to use. When used with direct
55 OGR access this is the layer name.
56 Default: 1
57 type=string[,string,...]
59 Types to be extracted
60 Input feature type
61 Options: point, line, boundary, centroid, area, face
62 Default: point,line,boundary,centroid,area,face
63 cats=range
65 Category values
66 Example: 1,3,7-9,13
67 where=sql_query
69 WHERE conditions of SQL statement without ’where’ keyword
70 Example: income < 1000 and population >= 10000
71 output=name [required]
73 Name for output vector map
74 file=name
76 Input text file with category numbers/number ranges to be extracted
77 If ’-’ given reads from standard input
78 random=integer
80 Number of random categories matching vector objects to extract
81 Number must be smaller than unique cat count in layer
82 new=integer
84 Desired new category value (enter -1 to keep original categories)
85 If new >= 0, attributes is not copied
86 Default: -1
87 dissolve_column=name
89 Name of attribute column for dissolving areas
90 Preserves category values
91
93 v.extract allows a user to select vector objects from an existing vec‐
94 tor map and creates a new map containing only the selected objects.
95 Database tables can be queried with SQL statements, if a connection is
96 established. Dissolving (optional) is based on the output categories.
97 If 2 adjacent areas have the same output category, the boundary is re‐
98 moved.
99 If cats, file, random or where options are not specified, all features
101 of given type and layer are extracted. Categories are not changed in
102 that case.
103
105 Only features with a category number in the selected layer will be ex‐
106 tracted. So if you want to extract boundaries (which are usually with‐
107 out category, as that information is normally held in the area’s cen‐
108 troid) you must first use v.category to add them, or use layer=-1.
109
111 The examples are intended for the North Carolina sample dataset:
112 Extract areas by category number with dissolving #1:
114 v.extract -d cats=1,2,3,4 input=soils_wake output=soil_groupa type=area new=0
115 produces a new vector soil_groupa, containing those areas from vector
117 soils which have category numbers 1 thru 4; any common boundaries are
118 dissolved, and all areas in the new map will be assigned category num‐
119 ber 0.
120 Extract areas by category number with dissolving #2:
122 v.extract -d cats=1-4 input=soils_wake output=soil_groupa type=area new=-1
123 produces a new vector map soil_groupa containing the areas from vector
125 soils which have categories 1 thru 4. Any common boundaries are dis‐
126 solved, all areas in the new map will retain their original category
127 numbers 1 thru 4, since new was set to -1.
128 Extract all areas and assign the same category to all:
130 v.extract input=soils_wake output=soil_groupa type=area new=1
131 produces a new vector map soil_groupa containing all areas from soils.
133 No common boundaries are dissolved, all areas of the new map will be
134 assigned category number 1.
135 Extract vectors with SQL:
137 v.extract input=markveggy.shp output=markveggy.1 new=13 \
138 where="(VEGTYPE = ’Wi’) or (VEGTYPE = ’PS’) or (PRIME_TYPE=’Wi’)"
139 produces a new vector map with category number 13 if the SQL statement
141 is fulfilled.
142 Extract vector features which have the given field empty:
144 v.extract input=lakes output=lakes_gaps where="FTYPE is NULL"
145 Extract vector features which have the given field not empty:
147 v.extract input=lakes output=lakes_ftype where="FTYPE not NULL"
148 Reverse extracting (behaves like selective vector objects deleting):
150 Remove meteorological stations from map which are located above 1000m:
151 # check what to delete:
152 v.db.select precip_30ynormals where="elev > 1000"
153 # perform reverse selection
154 v.extract -r input=precip_30ynormals output=precip_30ynormals_lowland \
155 where="elev > 1000"
156 # verify
157 v.db.select precip_30ynormals_lowland
158 Dissolving based on column attributes:
160 # check column names:
161 v.info -c zipcodes_wake
162 # reclass based on desired column:
163 v.reclass input=zipcodes_wake output=zipcodes_wake_recl_nam column=ZIPNAME
164 # verify:
165 v.info -c zipcodes_wake_recl_nam
166 v.db.select zipcodes_wake_recl_nam
167 # dissolve:
168 v.extract -d input=zipcodes_wake_recl_nam output=zipcodes_wake_regions
169 This produces a new vector map with common boundaries dissolved where
171 the reclassed attributes of adjacent (left/right) areas are identical.
172 Extract 3 random areas from geology map
174 v.extract input=geology output=random_geology type=area random=3
175 This creates a new map with three random categories matching areas.
176 Note that there may be more than one feature with the same category.
177
179 v.category, v.dissolve, v.reclass, GRASS SQL interface
180
182 R.L. Glenn, USDA, SCS, NHQ-CGIS
183 GRASS 6 port by Radim Blazek
184
186 Available at: v.extract source code (history)
187 Accessed: Saturday Jan 21 20:39:47 2023
189 Main index | Vector index | Topics index | Keywords index | Graphical
191 index | Full index
192 © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
194GRASS 8.2.1 v.extract(1)