16.3. Lesson: Importul și Exportul

Desigur, o bază de date care nu dispune de o modalitate de a migra facil datele. în interiorul și în afara ei, nu ar fi de mare folos. Din fericire, există o serie de instrumente care vă permit mutarea cu ușurință a datelor în interiorul și în afara PostGIS.

16.3.1. shp2pgsql

shp2pgsql is a commandline tool to import ESRI Shapefile to the database. Under Unix, you can use the following command for importing a new PostGIS table:

shp2pgsql -s <SRID> -c -D -I <path to shapefile> <schema>.<table> | \
  psql -d <databasename> -h <hostname> -U <username>

Sub Windows, procesul de import trebuie efectuat în două etape:

shp2pgsql -s <SRID> -c -D -I <path to shapefile> <schema>.<table> > import.sql
psql psql -d <databasename> -h <hostname> -U <username> -f import.sql

Este posibil să întâlniți această eroare:

ERROR:  operator class "gist_geometry_ops" does not exist for access method

This is a known issue regarding the creation in situ of a spatial index for the data you’re importing. To avoid the error, exclude the -I parameter. This will mean that no spatial index is being created directly, and you’ll need to create it in the database after the data have been imported. (The creation of a spatial index will be covered in the next lesson.)

16.3.2. pgsql2shp

pgsql2shp is a commandline tool to export PostGIS Tables, Views or SQL select queries. To do this under Unix:

pgsql2shp -f <path to new shapefile> -g <geometry column name> \
  -h <hostname> -U <username> <databasename> <table | view>

Pentru a exporta datele folosiți o interogare:

pgsql2shp -f <path to new shapefile> -g <geometry column name> \
  -h <hostname> -U <username> "<query>"

16.3.3. ogr2ogr

ogr2ogr is a very powerful tool to convert data into and from postgis to many data formats. ogr2ogr is part of the GDAL library and has to be installed separately. To export a table from PostGIS to GML, you can use this command:

ogr2ogr -f GML export.gml PG:'dbname=<databasename> user=<username>
        host=<hostname>' <Name of PostGIS-Table>

16.3.4. DB Manager

You may have noticed another option in the Database menu labeled DB Manager. This is a tool that provides a unified interface for interacting with spatial databases including PostGIS. It also allows you to import and export from databases to other formats. Since the next module is largely devoted to using this tool, we will only briefly mention it here.

16.3.5. In Conclusion

Importing and exporting data to and from the database can be done in many various ways. Especially when using disparate data sources, you will probably use these functions (or others like them) on a regular basis.

16.3.6. What’s Next?

Apoi, vom vedea cum se interoghează datele pe care le-am creat mai înainte.