GRASS GIS manual: v.in.ogr

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here

NAME

v.in.ogr - Imports vector data into a GRASS vector map using OGR library.

KEYWORDS

vector, import, OGR

SYNOPSIS

v.in.ogr

v.in.ogr --help

v.in.ogr [-flc2tojrewi] input=string [layer=string[,string,...]] [output=name] [spatial=xmin,ymin,xmax,ymax[,xmin,ymin,xmax,ymax,...]] [where=sql_query] [min_area=float] [type=string[,string,...]] [snap=float] [location=name] [columns=name[,name,...]] [encoding=string] [key=string] [geometry=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-f: List supported OGR formats and exit
-l: List available OGR layers in data source and exit
-c: Do not clean polygons (not recommended)
-2: Force 2D output even if input is 3D; Useful if input is 3D but all z coordinates are identical
-t: Do not create attribute table
-o: Override dataset projection (use location's projection)
-j: Perform projection check only and exit
-r: Limit import to the current region
-e: Extend region extents based on new dataset; Also updates the default region if in the PERMANENT mapset
-w: Change column names to lowercase characters
-i: Create the location specified by the "location" parameter and exit. Do not import the vector data.
--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=string [required]: OGR datasource name; Examples:
ESRI Shapefile: directory containing shapefiles
MapInfo File: directory containing mapinfo files
layer=string[,string,...]: OGR layer name. If not given, all available layers are imported; Examples:
ESRI Shapefile: shapefile name
MapInfo File: mapinfo file name
output=name: Name for output vector map
spatial=xmin,ymin,xmax,ymax[,xmin,ymin,xmax,ymax,...]: Import subregion only; Format: xmin,ymin,xmax,ymax - usually W,S,E,N
where=sql_query: WHERE conditions of SQL statement without 'where' keyword; Example: income < 1000 and inhab >= 10000
min_area=float: Minimum size of area to be imported (square meters); Smaller areas and islands are ignored. Should be greater than snap^2; Default: 0.0001
type=string[,string,...]: Optionally change default input type; Options: point, line, boundary, centroid; Default:; point: import area centroids as points; line: import area boundaries as lines; boundary: import lines as area boundaries; centroid: import points as centroids
snap=float: Snapping threshold for boundaries (map units); '-1' for no snap; Default: -1
location=name: Name for new location to create
columns=name[,name,...]: List of column names to be used instead of original names, first is used for category column
encoding=string: Encoding value for attribute data; Overrides encoding interpretation, useful when importing ESRI Shapefile
key=string: Name of column used for categories; If not given, categories are generated as unique values and stored in 'cat' column
geometry=name: Name of geometry column; If not given, all geometry columns from the input are used

DESCRIPTION

v.in.ogr imports vector data from files and database connections supported by the OGR library) into the current location and mapset.

If the layer parameter is not given, all available OGR layers are imported as separate GRASS layers into one GRASS vector map. If several OGR layer names are given, all these layers are imported as separate GRASS layers into one GRASS vector map.

The optional spatial parameter defines spatial query extents. This parameter allows the user to restrict the region to a spatial subset while importing the data. All vector features completely or partially falling into this rectangle subregion are imported. The -r current region flag is identical, but uses the current region settings as the spatial bounds (see g.region).

Supported Vector Formats

v.in.ogr uses the OGR library which supports various vector data formats including ESRI Shapefile, Mapinfo File, UK .NTF, SDTS, TIGER, IHO S-57 (ENC), DGN, GML, GPX, AVCBin, REC, Memory, OGDI, and PostgreSQL, depending on the local OGR installation. For details see the OGR web site. The OGR (Simple Features Library) is part of the GDAL library, hence GDAL needs to be installed to use v.in.ogr.

The list of actually supported formats can be printed by -f flag.

Topology cleaning

Topology cleaning on areas is automatically performed, but may fail in special cases. In these cases, a snap threshold value is estimated from the imported vector data and printed out at the end. The vector data can then be imported again with the suggested snap threshold value which is incremented by powers of 10 until either an estimated upper limit for the threshold value is reached or the topology cleaning on areas was successful. In some cases, manual cleaning might be required or areas are truly overlapping, e.g. buffers created with non-topological software.

The min_area threshold value is being specified as area size in map units with the exception of latitude-longitude locations in which it is being specified solely in square meters.

The snap threshold value is used to snap boundary vertices to each other if the distance in map units between two vertices is not larger than the threshold. Snapping is by default disabled with -1. See also the v.clean manual.

Overlapping polygons

When importing overlapping polygons, the overlapping parts will become new areas with multiple categories, one unique category for each original polygon. An original polygon will thus be converted to multiple areas with the same shared category. These multiple areas will therefore also link to the same entry in the attribute table. A single category value may thus refer to multiple non-overlapping areas which together represent the original polygon overlapping with another polygon. The original polygon can be recovered by using v.extract with the desired category value or where statement and the -d flag to dissolve common boundaries.

Location Creation

v.in.ogr attempts to preserve projection information when importing datasets if the source format includes projection information, and if the OGR driver supports it. If the projection of the source dataset does not match the projection of the current location v.in.ogr will report an error message ("Projection of dataset does not appear to match current location").

If the user wishes to ignore the difference between the apparent coordinate system of the source data and the current location, they may pass the -o flag to override the projection check.

If the user wishes to import the data with the full projection definition, it is possible to have v.in.ogr automatically create a new location based on the projection and extents of the file being read. This is accomplished by passing the name to be used for the new location via the location parameter. Upon completion of the command, a new location will have been created (with only a PERMANENT mapset), and the vector map will have been imported with the indicated output name into the PERMANENT mapset.

An interesting wrapper command around v.in.ogr is v.import which reprojects (if needed) the vector dataset during import to the projection of the current location.

NOTES

Table column names: supported characters

The characters which are eligible for table column names are limited by the SQL standard. Supported are:

[A-Za-z][A-Za-z0-9_]*

This means that SQL neither supports '.' (dots) nor '-' (minus) nor '#' in table column names. Also a table name must start with a character, not a number.

v.in.ogr converts '.', '-' and '#' to '_' (underscore) during import. The -w flag changes capital column names to lowercase characters as a convenience for SQL usage (lowercase column names avoid the need to quote them if the attribute table is stored in a SQL DBMS such as PostgreSQL). The columns parameter is used to define new column names during import.

The DBF database specification limits column names to 10 characters. If the default DB is set to DBF and the input data contains longer column/field names, they will be truncated. If this results in multiple columns with the same name then v.in.ogr will produce an error. In this case you will either have to modify the input data or use v.in.ogr's columns parameter to rename columns to something unique. (hint: copy and modify the list given with the error message). Alternatively, change the local DB with db.connect.

File encoding

When importing ESRI Shapefiles the OGR library tries to read the LDID/codepage setting from the .dbf file and use it to translate string fields to UTF-8. LDID "87 / 0x57" is treated as ISO8859_1 which may not be appropriate for many languages. Unfortunately it is not clear what other values may be appropriate (see example below). To change encoding the user can set up SHAPE_ENCODING environmental variable or simply to define encoding value using encoding parameter. Note that recoding support is new for GDAL/OGR 1.9.0.

Value for encoding also affects text recoding when importing DXF files. For other formats has encoding value no effect.

Defining the key column

Option key specifies the column name used for feature categories. This column must be integer. If not specified, categories numbers are generated starting with 1 and stored in the column named "cat".

Supports of multiple geometry columns

Starting with GDAL 1.11 the library supports multiple geometry columns in OGR. By default v.in.ogr reads all geometry columns from given layer. The user can choose desired geometry column by geometry option, see example below.

Latitude-longitude data: Vector postprocessing after import

For vector data like a grid, horizontal lines need to be broken at their intersections with vertical lines (v.clean ... tool=break).

EXAMPLES

The command imports various vector formats:

SHAPE files

v.in.ogr input=/home/user/shape_data/test_shape.shp output=grass_map

Alternate method:

v.in.ogr input=/home/user/shape_data layer=test_shape output=grass_map

Define encoding value for attribute data (in this example we expect attribute data in Windows-1250 encoding; ie. in Central/Eastern European languages that use Latin script, Microsoft Windows encoding).

v.in.ogr input=/home/user/shape_data/test_shape.shp output=grass_map encoding=cp1250

MapInfo files

v.in.ogr input=./ layer=mapinfo_test output=grass_map

Arc Coverage

We import the Arcs and Label points, the module takes care to build areas.

v.in.ogr input=gemeinden layer=LAB,ARC type=centroid,boundary output=mymap

E00 file

SDTS files

You have to select the CATD file.

v.in.ogr input=CITXCATD.DDF output=cities

TIGER files

v.in.ogr input=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all \
type=boundary,centroid snap=-1

PostGIS tables

Area example:

v.in.ogr input="PG:host=localhost dbname=postgis user=postgres" layer=polymap \
output=polygons type=boundary,centroid

Oracle Spatial maps

Note that you have to set the environment-variables ORACLE_BASE, ORACLE_SID, ORACLE_HOME and TNS_ADMIN accordingly.

v.in.ogr dsn=OCI:username/password@database_instance output=grasslayer layer=roads_oci

Multiple geometry columns

This example shows how to work with data which contain multiple geometry per feature. The number of geometry columns per feature can be checked by v.external together with -t flag.

v.external -t input=20141130_ST_UKSH.xml.gz
...
Okresy,point,1,DefinicniBod
Okresy,multipolygon,1,OriginalniHranice
Okresy,multipolygon,1,GeneralizovaneHranice
...

In our example layer "Okresy" has three geometry columns: "DefinicniBod", "OriginalniHranice" and "GeneralizovanaHranice". By default v.in.ogr reads data from all three geometry columns. The user can specify desired geometry column by geometry option, in this case the module will read geometry only from the specified geometry column. In the example below, the output vector map will contain only geometry saved in "OriginalniHranice" geometry column.

v.in.ogr input=20141130_ST_UKSH.xml.gz layer=Okresy geometry=OriginalniHranice

WARNINGS

If a message like "WARNING: Area size 1.3e-06, area not imported." appears, the min_area may be adjusted to a smaller value so that all areas are imported. Otherwise tiny areas are filtered out during import (useful to polish digitization errors or non-topological data).

If a message like "Try to import again, snapping with at least 1e-008: 'snap=1e-008'" appears, then the map to be imported contains topological errors. The message suggests a value for the snap parameter to be tried. For more details, see above in Topology Cleaning.

ERROR MESSAGES

DBMI-DBF driver error: SQL parser error: syntax error, unexpected DESC, expecting NAME processing 'DESC': indicates that a column name corresponds to a reserved SQL word (here: 'DESC'). A different column name should be used. The columns parameter can be used to assign different column names on the fly.
Projection of dataset does not appear to match the current location.: You need to create a location whose projection matches the data you wish to import. Try using location parameter to create a new location based upon the projection information in the file. If desired, you can then re-project it to another location with v.proj.

REFERENCES

OGR vector library
OGR vector library C API documentation

AUTHORS

Original author: Radim Blazek, ITC-irst, Trento, Italy
Location and spatial extent support by Markus Neteler and Paul Kelly
Various improvements by Markus Metz
Multiple geometry columns support by Martin Landa, OSGeoREL, Czech Technical University in Prague, Czech Republic

Last changed: $Date: 2017-08-21 14:52:37 -0700 (Mon, 21 Aug 2017) $

SOURCE CODE

Available at: v.in.ogr source code (history)