DESCRIPTION

v.in.ogr imports vector data using OGR library to GRASS vector map. OGR (Simple Features Library) is part of the GDAL library, so you need to install GDAL to use v.in.ogr.

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).

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.

Supported OGR Vector Formats

OGR library supports various vector data formats including ESRI Shapefile, Mapinfo File, UK .NTF, SDTS, TIGER, IHO S-57 (ENC), DGN, GML, AVCBin, REC, Memory, OGDI, and PostgreSQL depend on the local installation, for details see OGR web site.

List of locally supported formats can be printed by -f flag.

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.

NOTES

The characters used for table column names are limited. 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 cnames 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 cnames 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.

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 bellow). 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.

Option key specifies 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".

EXAMPLES

The command imports various vector formats:

SHAPE files

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

Alternate method:

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

MapInfo files

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

E00 file

SDTS files

You have to select the CATD file.

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

TIGER files

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

PostGIS tables

Area example:

v.in.ogr dsn="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

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 cnames 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

Radim Blazek, ITC-irst, Trento, Italy
Location and spatial extent support by Markus Neteler and Paul Kelly
Markus Metz

Last changed: $Date$