Formatele de Date Acceptate¶

Loading a Shapefile¶

To load a shapefile, start QGIS and click on the ^{Add Vector Layer} toolbar button, or simply press Ctrl+Shift+V. This will bring up a new window (see figure_vector_1).

Figure Vector 1:

Add Vector Layer Dialog

From the available options check File. Click on [Browse]. That will bring up a standard open file dialog (see figure_vector_2), which allows you to navigate the file system and load a shapefile or other supported data source. The selection box Filter allows you to preselect some OGR-supported file formats.

You can also select the encoding for the shapefile if desired.

Figure Vector 2:

Open an OGR Supported Vector Layer Dialog

Selecting a shapefile from the list and clicking [Open] loads it into QGIS. Figure_vector_3 shows QGIS after loading the alaska.shp file.

Figure Vector 3:

QGIS with Shapefile of Alaska loaded

Once a shapefile is loaded, you can zoom around it using the map navigation tools. To change the style of a layer, open the Layer Properties dialog by double clicking on the layer name or by right-clicking on the name in the legend and choosing Properties from the context menu. See section Meniul Stilului for more information on setting symbology of vector layers.

Improving Performance for Shapefiles¶

To improve the performance of drawing a shapefile, you can create a spatial index. A spatial index will improve the speed of both zooming and panning. Spatial indexes used by QGIS have a .qix extension.

Folosiți acești pași pentru a crea indexul:

• Load a shapefile by clicking on the ^{Add Vector Layer} toolbar button or pressing Ctrl+Shift+V.
• Open the Layer Properties dialog by double-clicking on the shapefile name in the legend or by right-clicking and choosing Properties from the context menu.

• În fila General, faceți clic pe butonul [Create Spatial Index].

Problem loading a shape .prj file¶

If you load a shapefile with a .prj file and QGIS is not able to read the coordinate reference system from that file, you will need to define the proper projection manually within the General tab of the Layer Properties dialog of the layer by clicking the [Specify...] button. This is due to the fact that .prj files often do not provide the complete projection parameters as used in QGIS and listed in the CRS dialog.

For the same reason, if you create a new shapefile with QGIS, two different projection files are created: a .prj file with limited projection parameters, compatible with ESRI software, and a .qpj file, providing the complete parameters of the used CRS. Whenever QGIS finds a .qpj file, it will be used instead of the .prj.

Încărcarea unui fișier cu texte delimitate¶

Click the toolbar icon ^{Add Delimited Text Layer} in the Manage layers toolbar to open the Create a Layer from a Delimited Text File dialog, as shown in figure_delimited_text_1.

Figure Delimited Text 1:

Delimited Text Dialog

First, select the file to import (e.g., qgis_sample_data/csv/elevp.csv) by clicking on the [Browse] button. Once the file is selected, QGIS attempts to parse the file with the most recently used delimiter. To enable QGIS to properly parse the file, it is important to select the correct delimiter. You can specify a delimiter by activating Custom delimiters, or by activating Regular expression delimiter and entering text into the Expression field. For example, to change the delimiter to tab, use \t (this is a regular expression for the tab character).

Once the file is parsed, set Geometry definition to Point coordinates and choose the X and Y fields from the dropdown lists. If the coordinates are defined as degrees/minutes/seconds, activate the DMS coordinates checkbox.

Finally, enter a layer name (e.g., elevp), as shown in figure_delimited_text_1. To add the layer to the map, click [OK]. The delimited text file now behaves as any other map layer in QGIS.

There is also a helper option that allows you to trim leading and trailing spaces from fields — Trim fields. Also, it is possible to Discard empty fields. If necessary, you can force a comma to be the decimal separator by activating Decimal separator is comma.

If spatial information is represented by WKT, activate the Well Known Text option and select the field with the WKT definition for point, line or polygon objects. If the file contains non-spatial data, activate No geometry (attribute only table) and it will be loaded as an ordinal table.

Additionaly, you can enable:

• Se folosește un index spațial pentru a îmbunătăți performanța afișării și pentru selectarea spațială a entităților.

• Folosește indexul subsetului.

• Watch file to watch for changes to the file by other applications while QGIS is running.

Încărcarea Vectorilor OpenStreetMap¶

QGIS integrates OpenStreetMap import as a core functionality.

• To connect to the OSM server and download data, open the menu Vector ‣ Openstreetmap ‣ Load data. You can skip this step if you already obtained an .osm XML file using JOSM, Overpass API or any other source.
• The menu Vector ‣ Openstreetmap ‣ Import topology from an XML file will convert your .osm file into a SpatiaLite database and create a corresponding database connection.
• The menu Vector ‣ Openstreetmap ‣ Export topology to SpatiaLite then allows you to open the database connection, select the type of data you want (points, lines, or polygons) and choose tags to import. This creates a SpatiaLite geometry layer that you can add to your project by clicking on the ^{Add SpatiaLite Layer} toolbar button or by selecting the Add SpatiaLite Layer... option from the Layer menu (see section Straturile SpatiaLite).

Crearea unei conexiuni stocate¶

The first time you use a PostGIS data source, you must create a connection to the PostgreSQL database that contains the data. Begin by clicking on the ^{Add PostGIS Layer} toolbar button, selecting the Add PostGIS Layer... option from the Layer menu, or typing Ctrl+Shift+D. You can also open the Add Vector Layer dialog and select Database. The Add PostGIS Table(s) dialog will be displayed. To access the connection manager, click on the [New] button to display the Create a New PostGIS Connection dialog. The parameters required for a connection are:

• Name: Un nume pentru această conexiune. Acesta poate fi identic cu cel al Bazei de Date.

• Service: Service parameter to be used alternatively to hostname/port (and potentially database). This can be defined in pg_service.conf.
• Host: Name of the database host. This must be a resolvable host name such as would be used to open a telnet connection or ping the host. If the database is on the same computer as QGIS, simply enter ‘localhost’ here.

• Port: Numărul portului pe care îl ascultă serverul bazei de date PostgreSQL. Portul implicit este 5432.

• Database: Numele bazei de date.

• SSL mode: How the SSL connection will be negotiated with the server. Note that massive speedups in PostGIS layer rendering can be achieved by disabling SSL in the connection editor. The following options are available:

  • Disable: Se încearcă doar o conexiune SSL necriptată.

  • Allow: Se încearcă o conexiune SSL. Dacă aceasta nu reușește, se încearcă o conexiune non-SSL.

  • Prefer (implicit): Se încearcă o conexiune SSL. Dacă aceasta nu reușește, se încearcă o conexiune non-SSL.

  • Require: Se încearcă doar o conexiune SSL.

• Username: Numele utilizatorului care va fi utilizat pentru conectarea la o bază de date.

• Password: Parola utilizată împreună cu Numele de utilizator pentru conectarea la baza de date.

Opțional, puteți activa următoarele casete:

• Salvare Nume de utilizator

• Salvare Parolă

• Căutare numai în coloanele_de_geometrie ale tabelului

• Nu se rezolvă tipul coloanelor nerestricționate (GEOMETRY)

• Căutare numai în schema ‘public’

• De asemenea, se listează tabelele fără geometrie

• Folosește metadatele tabelei de estimare

După ce s-au setat toți parametrii și toate opțiunile, puteți testa conexiunea, făcând clic pe butonul [Test Connect].

Încărcarea unui strat PostGIS¶

Once you have one or more connections defined, you can load layers from the PostgreSQL database. Of course, this requires having data in PostgreSQL. See section Importarea Datelor în PostgreSQL for a discussion on importing data into the database.

Pentru a încărca un strat PostGIS, efectuați următorii pași:

• If the Add PostGIS layers dialog is not already open, selecting the Add PostGIS Layer... option from the Layer menu or typing Ctrl+Shift+D opens the dialog.

• Alegeți conexiunea din lista verticală și faceți clic pe [Connect].

• Selectați sau deselectați De asemenea, se listează tabelele fără geometrie.

• Optionally, use some Search Options to define which features to load from the layer, or use the [Build query] button to start the Query builder dialog.

• Găsiți strat(urile) pe care doriți să le adăugați în lista de straturi disponibile.

• Select it by clicking on it. You can select multiple layers by holding down the Shift key while clicking. See section Constructorul de Interogări for information on using the PostgreSQL Query Builder to further define the layer.

• Clic pe butonul [Add] pentru a adăuga stratul la hartă.

Unele detalii despre straturile PostgreSQL¶

This section contains some details on how QGIS accesses PostgreSQL layers. Most of the time, QGIS should simply provide you with a list of database tables that can be loaded, and it will load them on request. However, if you have trouble loading a PostgreSQL table into QGIS, the information below may help you understand any QGIS messages and give you direction on changing the PostgreSQL table or view definition to allow QGIS to load it.

QGIS requires that PostgreSQL layers contain a column that can be used as a unique key for the layer. For tables, this usually means that the table needs a primary key, or a column with a unique constraint on it. In QGIS, this column needs to be of type int4 (an integer of size 4 bytes). Alternatively, the ctid column can be used as primary key. If a table lacks these items, the oid column will be used instead. Performance will be improved if the column is indexed (note that primary keys are automatically indexed in PostgreSQL).

If the PostgreSQL layer is a view, the same requirement exists, but views do not have primary keys or columns with unique constraints on them. You have to define a primary key field (has to be integer) in the QGIS dialog before you can load the view. If a suitable column does not exist in the view, QGIS will not load the layer. If this occurs, the solution is to alter the view so that it does include a suitable column (a type of integer and either a primary key or with a unique constraint, preferably indexed).

QGIS offers a checkbox Select at id that is activated by default. This option gets the ids without the attributes which is faster in most cases. It can make sense to disable this option when you use expensive views.

DB Manager¶

QGIS comes with a core plugin named ^{DB Manager}. It can be used to load shapefiles and other data formats, and it includes support for schemas. See section Plugin-ul DB Manager for more information.

shp2pgsql¶

PostGIS includes an utility called shp2pgsql that can be used to import shapefiles into a PostGIS-enabled database. For example, to import a shapefile named lakes.shp into a PostgreSQL database named gis_data, use the following command:

shp2pgsql -s 2964 lakes.shp lakes_new | psql gis_data

This creates a new layer named lakes_new in the gis_data database. The new layer will have a spatial reference identifier (SRID) of 2964. See section Lucrul cu Proiecții for more information on spatial reference systems and projections.

ogr2ogr¶

Besides shp2pgsql and DB Manager, there is another tool for feeding geodata in PostGIS: ogr2ogr. This is part of your GDAL installation.

Pentru a importa un strat în PostGIS, efectuați următorii pași:

ogr2ogr -f "PostgreSQL" PG:"dbname=postgis host=myhost.de user=postgres
password=topsecret" alaska.shp

This will import the shapefile alaska.shp into the PostGIS database postgis using the user postgres with the password topsecret on host server myhost.de.

Note that OGR must be built with PostgreSQL to support PostGIS. You can verify this by typing (in )

ogrinfo --formats | grep -i post

If you prefer to use PostgreSQL’s COPY command instead of the default INSERT INTO method, you can export the following environment variable (at least available on and ):

export PG_USE_COPY=YES

ogr2ogr does not create spatial indexes like shp2pgsl does. You need to create them manually, using the normal SQL command CREATE INDEX afterwards as an extra step (as described in the next section Îmbunătățirea Performanței).

Îmbunătățirea Performanței¶

Retrieving features from a PostgreSQL database can be time-consuming, especially over a network. You can improve the drawing performance of PostgreSQL layers by ensuring that a PostGIS spatial index exists on each layer in the database. PostGIS supports creation of a GiST (Generalized Search Tree) index to speed up spatial searches of the data (GiST index information is taken from the PostGIS documentation available at http://postgis.refractions.net).

Sintaxa pentru crearea unui index GIST este:

CREATE INDEX [indexname] ON [tablename]
  USING GIST ( [geometryfield] GIST_GEOMETRY_OPS );

Note that for large tables, creating the index can take a long time. Once the index is created, you should perform a VACUUM ANALYZE. See the PostGIS documentation (POSTGIS-PROJECT Literatură și Referințe Web) for more information.

Următorul este un exemplu de creare a unui index GIST:

gsherman@madison:~/current$ psql gis_data
Welcome to psql 8.3.0, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

gis_data=# CREATE INDEX sidx_alaska_lakes ON alaska_lakes
gis_data-# USING GIST (the_geom GIST_GEOMETRY_OPS);
CREATE INDEX
gis_data=# VACUUM ANALYZE alaska_lakes;
VACUUM
gis_data=# \q
gsherman@madison:~/current$

Utilizare¶

• Importați datele în PostGIS (Importarea Datelor în PostgreSQL) folosind, de exemplu, plugin-ul DB Manager.

• Use the PostGIS command line interface to issue the following command (in this example, “TABLE” is the actual name of your PostGIS table): gis_data=# update TABLE set the_geom=ST_Shift_Longitude(the_geom);
• If everything went well, you should receive a confirmation about the number of features that were updated. Then you’ll be able to load the map and see the difference (Figure_vector_5).

Crearea unui nou strat SpatiaLite¶

Dacă doriți să creați un nou strat SpatiaLite, vă rugăm să consultați secțiunea Crearea unui nou strat SpatiaLite.

Crearea unei conexiuni stocate¶

The first time you use an Oracle Spatial data source, you must create a connection to the database that contains the data. Begin by clicking on the ^{Add Orcale Spatial Layer} toolbar button, selecting the Add Orcale Spatial Layer... option from the Layer menu, or typing Ctrl+Shift+O. To access the connection manager, click on the [New] button to display the Create a New Oracle Spatial Connection dialog. The parameters required for a connection are:

• Name: Un nume pentru această conexiune. Poate fi identic cu cel al Bazei de Date.

• Database: SID-ul sau SERVICE_NAME-ul instanței Oracle.

• Host: Name of the database host. This must be a resolvable host name such as would be used to open a telnet connection or ping the host. If the database is on the same computer as QGIS, simply enter ‘localhost’ here.

• Port: Numărul portului pe care îl monitorizează serverul bazei de date Oracle. Portul implicit este 1521.

• Username: Numele utilizatorului care va fi utilizat pentru conectarea la baza de date.

• Password: Parola utilizată împreună cu Numele de utilizator pentru conectarea la baza de date.

Opțional, puteți activa următoarele casete:

• Save Username Indicates whether to save the database username in the connection configuration.
• Save Password Indicates whether to save the database password in the connection settings.
• Only look in meta data table Restricts the displayed tables to those that are in the all_sdo_geom_metadata view. This can speed up the initial display of spatial tables.
• Only look for user’s tables When searching for spatial tables, restrict the search to tables that are owned by the user.

• De asemenea, se listează tabelele fără geometrie Indică faptul că, de asemenea, tabelele fără geometrie ar trebui să fie enumerate în mod implicit.

• Use estimated table statistics for the layer metadata When the layer is set up, various metadata are required for the Oracle table. This includes information such as the table row count, geometry type and spatial extents of the data in the geometry column. If the table contains a large number of rows, determining this metadata can be time-consuming. By activating this option, the following fast table metadata operations are done: Row count is determined from all_tables.num_rows. Table extents are always determined with the SDO_TUNE.EXTENTS_OF function, even if a layer filter is applied. Table geometry is determined from the first 100 non-null geometry rows in the table.

• Listează doar tipurile de geometrie existente Va lista doar tipurile de geometrie existente și nu propune adăugarea altora.

După ce s-au setat toți parametrii și toate opțiunile, puteți testa conexiunea, făcând clic pe butonul [Test Connect].

Încărcarea Stratului Oracle Spatial¶

Once you have one or more connections defined, you can load layers from the Oracle database. Of course, this requires having data in Oracle.

Pentru a încărca un strat Oracle Spatial, efectuați următorii pași:

• If the Add Oracle Spatial layers dialog is not already open, click on the ^{Add Oracle Spatial Layer} toolbar button.

• Alegeți conexiunea din lista verticală și faceți clic pe [Connect].

• Selectați sau deselectați De asemenea, se listează tabelele fără geometrie.

• Optionally, use some Search Options to define which features to load from the layer or use the [Build query] button to start the Query builder dialog.

• Găsiți strat(urile) pe care doriți să le adăugați în lista de straturi disponibile.

• Select it by clicking on it. You can select multiple layers by holding down the Shift key while clicking. See section Constructorul de Interogări for information on using the Oracle Query Builder to further define the layer.

• Clic pe butonul [Add] pentru a adăuga stratul la hartă.