v.out.postgisgrass - Online in the Cloud

PROGRAM:

NAME

v.out.postgis - Exports a vector map layer to PostGIS feature table.

KEYWORDS

vector, export, PostGIS, simple features, topology, 3D

SYNOPSIS

v.out.postgis
v.out.postgis --help
v.out.postgis [-tl2] input=name [type=string[,string,...]] [layer=string]
output=string [output_layer=name] [output_link=name]
[options=key=value[,key=value,...]] [--overwrite] [--help] [--verbose] [--quiet]
[--ui]

Flags:
-t
Do not export attribute table

-l
Export PostGIS topology instead of simple features

-2
Force 2D output even if input is 3D
Useful if input is 3D but all z coordinates are identical

--overwrite
Allow output files to overwrite existing files

--help
Print usage summary

--verbose
Verbose module output

--quiet
Quiet module output

--ui
Force launching GUI dialog

Parameters:
input=name [required]
Name of input vector map

type=string[,string,...]
Input feature type
Options: point, line, boundary, centroid, area, face, kernel, auto
Default: auto

layer=string
Layer number or name
Default: 1

output=string [required]
Name for output PostGIS datasource
Starts with ’PG’ prefix, eg. ’PG:dbname=grass’

output_layer=name
Name for output PostGIS layer
If not specified, input name is used

output_link=name
Name for output vector map defined as a link to the PostGIS feature table
If not specified, the vector link is not created. The link can be also manually
created by ’v.external’ module.

options=key=value[,key=value,...]
Creation options
Examples:
’FID=cat’: define feature id column ’cat’
’GEOMETRY_NAME=wkb_geometry’: define geometry column ’wkb_geometry’
’SPATIAL_INDEX=NO’: do not create spatial index on geometry column

DESCRIPTION

v.out.postgis exports an existing GRASS vector map layer to PostGIS feature table.
Features without category are skipped.

By default GRASS GIS topological features are converted into simple features (see OGC
Simple Feature Access specification for details). Flag -l allows to export vector features
as topological elements stored in PostGIS Topology schema. Note that topological export
requires PostGIS version 2 or later.

Additional creation options can be defined by options parameter:

· FID=<column> - name of column which will be used as primary key (feature id),
default: fid

· GEOMETRY_NAME=<column> name of column which will be used for storing geometry data
in feature table, default: geom

· SPATIAL_INDEX=YES|NO - enable/disable creating spatial index on geometry column,
default: YES

· PRIMARY_KEY=YES|NO - enable/disable adding primary key on FID column, default: YES

· SRID=<value> - spatial reference identifier, default: not defined
PostGIS Topology related options (relevant only for -l flag):

· TOPOSCHEMA_NAME=<schema name> - name of PostGIS Topology schema, default:
topo_<input>

· TOPOGEOM_NAME=<column> - name of column which will be used for storing
topogeometry data in feature table, default: topo

· TOPO_TOLERANCE=<value> - tolerance for PostGIS Topology schema, see CreateTopology
function for defails, default: 0

· TOPO_GEO_ONLY=YES|NO - store in PostGIS Topology schema only data relevant to
Topo-Geo data model, default: NO

Creation options are comma-separated pairs (key=value), the options are case-insensitive.
Note that options defined by v.external.out are ignored by v.out.postgis.

v.out.postgis optionally also creates a new vector map in the current mapset if
output_link is defined.

NOTES

By default v.out.postgis exports vector data as simple features, ie. boundaries and
centroids (forming topological areas) become polygons, isles become holes. Geometry of
simple feature elements is stored in PostGIS feature table in the column named "geom".
Name of the geometry column can be changed by options=GEOMETRY_NAME=<column>. Note that
for exporting vector features as simple features can be alternatively used PostgreSQL
driver from OGR library through v.out.ogr module.

Also note that it’s allowed to store in the feature table only features of the same type,
ie. mixing of points and lines is not currently possible. The feature type is determined
for output feature table from the first vector feature accessing data sequentially
(type=auto). Vector features of other types are during export skipped. User can choose
preferable feature type by type parameter. Only single type is currently allowed (see TODO
section for details).

v.out.postgis currently supports only three basic output simple feature types: Points,
Linestrings and Polygons. Also 3D features of the same type are supported, eg. 3D points
are exported as PointZ simple feature. Faces are exported as 3D polygons. 3D features are
written to the output automatically if input vector map is 3D. If -2 flag is given then
the output is always 2D (z-coordinate is silently ignored for 3D input vector maps).

Multigeometries are not currently supported. Features with the same category are exported
as multiple singe features.

v.out.postgis also allows exporting vector features as topological elements in PostGIS
Topology schema. PostGIS Topology extension uses three tables to store basic topological
elements which forms topological objects like areas or isles in GRASS terminology. Nodes
(0-dimensional topological elements) are stored in "node" table, edges (1-dimensional
elements) in "edge" table and faces (2-dimensional elements) in "face" table.

· GRASS nodes are stored in node table

· GRASS points are stored in node table as regular nodes

· GRASS centroids are stored in node table as regular nodes ("containing_face"
refers to related area)

· GRASS lines are stored in edge table

· GRASS boundaries are stored in edge table

· GRASS areas are stored in face table
Tables node, edge and face are stored in given topological schema. By default
v.out.postgis defines its name as topo_<input>. Alternatively, the name for topology
schema can be defined by options=TOPOSCHEMA_NAME=<name>.

EXAMPLES

Export Simple Features
Export vector map "urbanarea" as feature table "urbanarea" located in database "grass",
schema "public". Note that this database schema is automatically used when not defined by
the user.
v.out.postgis input=urbanarea output="PG:dbname=grass"
GRASS areas are converted into polygons, isles into holes. We can check the number or
created polygons by simple SQL query below.
db.select driver=pg database=grass \
sql="SELECT ST_GeometryType(geom) as geom_type, count(*) from urbanarea group by geom_type"
geom_type|count
ST_Polygon|657
Note: same procedure can be done by v.out.ogr module, eg.
v.out.ogr input=urbanarea output="PG:dbname=grass" format=PostgreSQL
In this case GRASS vector data are exported to PostGIS database using OGR library, namely
using PostgreSQL driver. Contrary to the v.out.ogr module, v.out.postgis is using directly
PostGIS data provider which is part of GRASS vector engine. Beside that, v.out.postgis is
optimized for PostGIS export including topological access to the data.

Export data into specific database schema
Database schema for storing exported data can be defined by output_layer as
<schema_name>.<table_name>. If the specified schema doesn’t exist in the database, then
it’s automatically created.

Export vector map "bridges" as feature table in database schema "grassout".
v.out.postgis input=bridges output="PG:dbname=grass" output_layer=grassout.bridges

Export data with creation options
Example below demonstrates how to define name for geometry column and disable building
spatial index. Spatial reference system is defined by srid identifier which corresponds in
this case with EPSG 3358 (North Carolina dataset).
v.out.postgis input=roadsmajor output="PG:dbname=grass" options="GEOMETRY_NAME=wkb_geometry,SPATIAL_INDEX=NO,SRID=3358"

Link exported data
Exported data can be linked as vector map created in the current mapset by specifying
output_link parameter. In the example below vector map "busstopsall" from PERMANENT mapset
is exported into "grass" PostGIS database. v.out.postgis after successful export also
creates in the current mapset GRASS vector map as a link to the PostGIS feature table.
v.out.postgis input=busstopsall@PERMANENT output="PG:dbname=grass" output_link=busstopsall_pg
Created link can be checked by v.info:
v.info busstopsall_pg
...
|----------------------------------------------------------------------------|
| Map format: PostGIS (PostgreSQL) |
| DB table: public.busstopsall |
| DB name: grass |
| Geometry column: geom |
| Feature type: point |
| Topology: pseudo (simple features) |
|----------------------------------------------------------------------------|
...

Export data without attributes
v.out.postgis allows ignoring attributes when exporting vector features by specifying -t
flag. Command below exports vector features without attributes. The feature will contain
only two columns, the fid and geometry column.
v.out.postgis -t input=railroads output="PG:dbname=grass"

Export topological data
By default v.out.postgis exports data as simple features. Flag -l allows exporting data as
topological elements instead of simple features. Export topological elements is stored in
PostGIS Topology schema.
v.out.postgis -l input=busroutesall output="PG:dbname=grass"
For more info about PostGIS Topology implementation in GRASS see the wiki page.

TODO

· Multi-feature export

· Allow mixed features (points, lines)

· Support other simple feature types like GeometryCollection and others

· Implement missing options from v.out.ogr: -a, -s, -c, -p, -n

· Add options: cats, where

REQUIREMENTS

· PostGIS 2.x or later for topological export (flag -l)

REFERENCES

· OGC Simple Feature Access specification

· PostGIS Topology documentation

· GRASS-PostGIS data provider

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