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

NAME

6       v.external   - Creates a new pseudo-vector map as a link to an OGR-sup‐
7       ported layer or a PostGIS feature table.
8

KEYWORDS

10       vector, import, external, OGR, PostGIS, level1
11

SYNOPSIS

13       v.external
14       v.external --help
15       v.external  [-ojfltb]  input=string   [layer=name]    [where=sql_query]
16       [output=name]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]
17
18   Flags:
19       -o
20           Override projection check (use current location’s projection)
21           Assume  that  the  dataset  has  the same projection as the current
22           location
23
24       -j
25           Perform projection check only and exit
26
27       -f
28           List supported formats and exit
29
30       -l
31           List available layers in data source and exit
32
33       -t
34           List available layers including feature type  in  data  source  and
35           exit
36           Format: layer name,type,projection check,geometry
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38       -b
39           Do not build topology
40           Advantageous when handling a large number of points
41
42       --overwrite
43           Allow output files to overwrite existing files
44
45       --help
46           Print usage summary
47
48       --verbose
49           Verbose module output
50
51       --quiet
52           Quiet module output
53
54       --ui
55           Force launching GUI dialog
56
57   Parameters:
58       input=string [required]
59           Name of input OGR or PostGIS data source
60           Examples:
61           ESRI Shapefile: directory containing a shapefile
62           MapInfo File: directory containing a mapinfo file
63           PostGIS database: connection string, eg. ’PG:dbname=db user=grass’
64
65       layer=name
66           Name of OGR layer or PostGIS feature table to be linked
67           Examples:
68           ESRI Shapefile: shapefile name
69           MapInfo File: mapinfo file name
70           PostGIS database: table name
71
72       where=sql_query
73           WHERE conditions of SQL statement without ’where’ keyword
74           Example: income < 1000 and population >= 10000
75
76       output=name
77           Name for output GRASS vector map (default: input layer)
78

DESCRIPTION

80       v.external  creates  new  vector map as a link to external OGR layer or
81       PostGIS feature table. OGR (Simple Features Library)  is  part  of  the
82       GDAL  library, so you need to install GDAL to use v.external for exter‐
83       nal OGR layers. Note that a PostGIS feature table can  be  linked  also
84       using  built-in  GRASS-PostGIS  data driver (requires GRASS to be built
85       with PostgreSQL support).
86

NOTES

88       The simple feature data model used by OGR (or PostGIS) is very  differ‐
89       ent  from  the topological format used by GRASS. Instead of true topol‐
90       ogy, so called ’pseudo topology’ is created for data linked by v.exter‐
91       nal.  User  should  learn  the  difference  between  those two formats,
92       because some modules working correctly with GRASS native data, can pro‐
93       duce wrong results with input vector maps created by v.external.
94
95       Limitations:
96
97       Due  to  these data model differences v.external does not work with all
98       data formats. In general, for all formats that do not have a key column
99       (e.g.  SHAPE file), attributes are not accessible, and attributes would
100       get lost when modifying the geometries. Therefore it is  generally  not
101       safe  to  link  vector  data with v.external. In many cases it does not
102       make sense to use v.external linked data with simple features,  instead
103       vector  data  should  be imported with v.import or v.in.ogr to get true
104       topology support. Importantly, point  cloud  data  which  do  not  have
105       topology,  can  be  linked  with  v.external  as  long  as there are no
106       attributes attached to these point cloud data, or if the format of  the
107       point cloud data has a key column that allows linking vector geometries
108       to attributes.
109
110       See v.db.connect for an example of maintaining attributes  in  external
111       DBMS in also writable mode.
112
113   Supported OGR vector formats
114       To list supported OGR formats, type
115       v.external -f
116       For details see GDAL web site.
117

EXAMPLES

119   ESRI Shapefile
120       Assuming    that    ’test_shape.shp’    is    located    in   directory
121       ’/home/user/shape_data’.
122       v.external input=/home/user/shape_data layer=test_shape output=grass_map
123
124   PostGIS layers
125       By default, PostGIS links are created by built-in PostGIS support,  ie.
126       using GRASS-PostGIS data driver. If the environment variable GRASS_VEC‐
127       TOR_OGR exists, or GRASS is compiled without  PostgreSQL  support  then
128       GRASS will use OGR-PostgreSQL driver for creating a link.
129
130       List of layers for given data source can be printed by -l flag.
131       v.external input="PG:host=localhost user=postgres dbname=postgis" -l
132       ...
133       polymap
134       ...
135       v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap
136       Note:  Authentication details (user password) can be preferably defined
137       by db.login.
138
139   MapInfo files
140       Assuming that ’mapinfo_test’ MapInfo file is  located  in  the  current
141       directory (".").
142       v.external input=./ layer=mapinfo_test output=grass_map
143
144   SDTS files
145       Note: you have to select the CATD file
146       v.external input=CITXCATD.DDF output=cities
147
148   TIGER files
149       v.external input=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all
150
151   Linking subset of features
152       By  where  option only subset of features can be linked. In the example
153       below only one feature (in this case a vector tile) will be linked as a
154       new GRASS vector map.
155       v.external in="PG:dbname=tiles" layer=wrs2_descending where="pr=191026"
156       ...
157       Number of areas: 1
158       ...
159

REFERENCES

161       OGR vector library C API documentation
162

SEE ALSO

164         v.external.out,  v.clean,  v.db.connect, v.import, v.in.db, v.in.ogr,
165       v.out.ogr
166
167       GDAL Library
168       PostGIS
169
170       See also GRASS user wiki page for more examples.
171

AUTHORS

173       Radim Blazek, ITC-Irst, Trento, Italy
174       PostGIS support by Martin Landa, GeoForAll (OSGeoREL) Lab, Czech  Tech‐
175       nical University in Prague, Czech Republic
176
177       Last changed: $Date: 2017-11-18 09:57:44 +0100 (Sat, 18 Nov 2017) $
178

SOURCE CODE

180       Available at: v.external source code (history)
181
182       Main  index  | Vector index | Topics index | Keywords index | Graphical
183       index | Full index
184
185       © 2003-2019 GRASS Development Team, GRASS GIS 7.4.4 Reference Manual
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189GRASS 7.4.4                                                      v.external(1)
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