Come Iniziare¶

Installazione¶

Installation of QGIS is very simple. Standard installer packages are available for MS Windows and Mac OS X. For many flavors of GNU/Linux, binary packages (rpm and deb) or software repositories are provided to add to your installation manager. Get the latest information on binary packages at the QGIS website at http://download.qgis.org.

Dati campione¶

The user guide contains examples based on the QGIS sample dataset.

The Windows installer has an option to download the QGIS sample dataset. If checked, the data will be downloaded to your My Documents folder and placed in a folder called GIS Database. You may use Windows Explorer to move this folder to any convenient location. If you did not select the checkbox to install the sample dataset during the initial QGIS installation, you may do one of the following:

• usare dati GIS che hai già;

• Download sample data from http://qgis.org/downloads/data/qgis_sample_data.zip
• Uninstall QGIS and reinstall with the data download option checked (only recommended if the above solutions are unsuccessful)

For GNU/Linux and Mac OS X, there are not yet dataset installation packages available as rpm, deb or dmg. To use the sample dataset, download the file qgis_sample_data as a ZIP archive from http://qgis.org/downloads/data and unzip the archive on your system.

The Alaska dataset includes all GIS data that are used for examples and screenshots in the user guide; it also includes a small GRASS database. The projection for the QGIS sample dataset is Alaska Albers Equal Area with units feet. The EPSG code is 2964.

PROJCS["Albers Equal Area",
GEOGCS["NAD27",
DATUM["North_American_Datum_1927",
SPHEROID["Clarke 1866",6378206.4,294.978698213898,
AUTHORITY["EPSG","7008"]],
TOWGS84[-3,142,183,0,0,0,0],
AUTHORITY["EPSG","6267"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,
AUTHORITY["EPSG","9108"]],
AUTHORITY["EPSG","4267"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["standard_parallel_1",55],
PARAMETER["standard_parallel_2",65],
PARAMETER["latitude_of_center",50],
PARAMETER["longitude_of_center",-154],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["us_survey_feet",0.3048006096012192]]

If you intend to use QGIS as a graphical front end for GRASS, you can find a selection of sample locations (e.g., Spearfish or South Dakota) at the official GRASS GIS website, http://grass.osgeo.org/download/sample-data/.

Sample Session¶

Now that you have QGIS installed and a sample dataset available, we would like to demonstrate a short and simple QGIS sample session. We will visualize a raster and a vector layer. We will use the landcover raster layer, qgis_sample_data/raster/landcover.img, and the lakes vector layer, qgis_sample_data/gml/lakes.gml.

Starting and Stopping QGIS¶

In section Sample Session you already learned how to start QGIS. We will repeat this here, and you will see that QGIS also provides further command line options.

• Assuming that QGIS is installed in the PATH, you can start QGIS by typing qgis at a command prompt or by double clicking on the QGIS application link (or shortcut) on the desktop or in the Applications menu.
• Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.
• Double click the icon in your Applications folder. If you need to start QGIS in a shell, run /path-to-installation-executable/Contents/MacOS/Qgis.

To stop QGIS, click the menu option File QGIS ‣ Quit, or use the shortcut Ctrl+Q.

Opzioni linea di comando¶

QGIS supports a number of options when started from the command line. To get a list of the options, enter qgis --help on the command line. The usage statement for QGIS is:

qgis --help
QGIS - 2.6.0-Brighton 'Brighton' (exported)
QGIS is a user friendly Open Source Geographic Information System.
Usage: /usr/bin/qgis.bin [OPTION] [FILE]
OPTION:
      [--snapshot filename]   emit snapshot of loaded datasets to given file
      [--width width] width of snapshot to emit
      [--height height]       height of snapshot to emit
      [--lang language]       use language for interface text
      [--project projectfile] load the given QGIS project
      [--extent xmin,ymin,xmax,ymax]  set initial map extent
      [--nologo]      hide splash screen
      [--noplugins]   don't restore plugins on startup
      [--nocustomization]     don't apply GUI customization
      [--customizationfile]   use the given ini file as GUI customization
      [--optionspath path]    use the given QSettings path
      [--configpath path]     use the given path for all user configuration
      [--code path]   run the given python file on load
      [--defaultui]   start by resetting user ui settings to default
      [--help]                this text

FILE:
  Files specified on the command line can include rasters,
  vectors, and QGIS project files (.qgs):
   1. Rasters - supported formats include GeoTiff, DEM
      and others supported by GDAL
   2. Vectors - supported formats include ESRI Shapefiles
      and others supported by OGR and PostgreSQL layers using
      the PostGIS extension

Opzioni linea di comando --snapshot

L’opzione consente di catturare una schermata in formato PNG della mappa. Utile quando hai molti progetti e vuoi generare schermate dai propri dati.

Il file PNG generato ha una risoluzione di 800x600 pixels. Puoi adattare la risoluzione grazie agli argomenti “–width” e “–height” da riga di comando. Puoi anche aggiungere il nome del file dopo l’argomento “–snapshot”.

Opzioni linea di comando --lang

Based on your locale, QGIS selects the correct localization. If you would like to change your language, you can specify a language code. For example, --lang=it starts QGIS in italian localization.

Opzioni linea di comando --project

Starting QGIS with an existing project file is also possible. Just add the command line option --project followed by your project name and QGIS will open with all layers in the given file loaded.

Opzioni linea di comando --extent

Per avviare QGIS con un specifica estensione devi aggiungere i confini della bounding box in questo ordine e separati da una virgola:

--extent xmin,ymin,xmax,ymax

Opzioni linea di comando --nologo

This command line argument hides the splash screen when you start QGIS.

Opzioni linea di comando --noplugins

Se all’avvio di QGIS si verificano problemi con i plugin puoi evitare di caricarli con questa opzione. I plugin rimarranno comunque disponibili nel Gestore plugin.

Opzioni linea di comando --customizationfile

Usando questa opzione puoi specificare un file di personalizzazione dell’interfaccia grafica che verrà caricato all’avvio.

Opzioni linea di comando --nocustomization

Usando questa opzione le personalizzazioni dell’interfaccia non verranno applicate all’avvio.

Opzioni linea di comando --optionspath

You can have multiple configurations and decide which one to use when starting QGIS with this option. See Opzioni dell’interfaccia grafica (GUI) to confirm where the operating system saves the settings files. Presently, there is no way to specify a file to write settings to; therefore, you can create a copy of the original settings file and rename it. The option specifies path to directory with settings. For example, to use /path/to/config/QGIS/QGIS2.ini settings file, use option:

--optionspath /path/to/config/

Opzioni linea di comando --configpath

This option is similar to the one above, but furthermore overrides the default path for user configuration (~/.qgis2) and forces QSettings to use this directory, too. This allows users to, for instance, carry a QGIS installation on a flash drive together with all plugins and settings.

Opzioni linea di comando --code

This option can be used to run a given python file directly after QGIS has started.

Per esempio, se hai un file python load_alaska.py con il seguente contenuto:

from qgis.utils import iface
raster_file = "/home/gisadmin/Documents/qgis_sample_data/raster/landcover.img"
layer_name = "Alaska"
iface.addRasterLayer(raster_file, layer_name)

Assuming you are in the directory where the file load_alaska.py is located, you can start QGIS, load the raster file landcover.img and give the layer the name ‘Alaska’ using the following command: qgis --code load_alaska.py

Progetti¶

The state of your QGIS session is considered a project. QGIS works on one project at a time. Settings are considered as being either per-project or as a default for new projects (see section Opzioni dell’interfaccia grafica (GUI)). QGIS can save the state of your workspace into a project file using the menu options Project ‣ Save or Project ‣ Save As....

Load saved projects into a QGIS session using Project ‣ Open..., Project ‣ New from template or Project ‣ Open Recent ‣.

If you wish to clear your session and start fresh, choose Project ‣ New. Either of these menu options will prompt you to save the existing project if changes have been made since it was opened or last saved.

Le informazioni salvate nel file di progetto includono:

• Layer aggiunti

• Which layers can be queried
• Layer properties, including symbolization and styles

• Proiezione usata per la mappa

• Ultima estensione della mappa

• Print Composers
• Print Composer elements with settings
• Print Composer atlas settings
• Digitizing settings
• Table Relations
• Project Macros
• Project default styles
• Plugins settings
• QGIS Server settings from the OWS settings tab in the Project properties
• Queries stored in the DB Manager

The project file is saved in XML format, so it is possible to edit the file outside QGIS if you know what you are doing. The file format has been updated several times compared with earlier QGIS versions. Project files from older QGIS versions may not work properly anymore. To be made aware of this, in the General tab under Settings ‣ Options you can select:

• Prompt to save project and data source changes when required
• Warn when opening a project file saved with an older version of QGIS

Whenever you save a project in QGIS a backup of the project file is made with the extension ~.

Output¶

There are several ways to generate output from your QGIS session. We have discussed one already in section Progetti, saving as a project file. Here is a sampling of other ways to produce output files:

• Menu option Project ‣ ^{Save as Image} opens a file dialog where you select the name, path and type of image (PNG,JPG and many other formats). A world file with extension PNGW or JPGW saved in the same folder georeferences the image.
• Menu option Project ‣ DXF Export ... opens a dialog where you can define the ‘Symbology mode’, the ‘Symbology scale’ and vector layers you want to export to DXF. Through the ‘Symbology mode’ symbols from the original QGIS Symbology can be exported with high fidelity.
• Menu option Project ‣ New Print Composer opens a dialog where you can layout and print the current map canvas (see section Compositore di stampe).