Noțiuni de bază¶

Acest capitol oferă o privire de ansamblu rapidă asupra instalării QGIS, a descărcării unor date eșantion din pagina web QGIS și a rulării unei prime și simple sesiuni de vizualizare a straturilor raster și vectoriale.

Instalare¶

Instalarea QGIS este foarte simplă. Pentru MS Windows și Mac OS X sunt disponibile pachete de instalare standard. Pentru mai multe distribuții de pachete binare GNU/Linux (rpm si deb) există depozite software care pot fi adăugate la managerul de instalare. Cele mai recente informații cu privire la pachetele binare se pot obține de pe site-ul web QGIS la http://download.qgis.org.

Instalarea de la sursă¶

If you need to build QGIS from source, please refer to the installation instructions. They are distributed with the QGIS source code in a file called ‘INSTALL’. You can also find it online at http://htmlpreview.github.io/?https://raw.github.com/qgis/QGIS/master/doc/INSTALL.html

Instalarea pe un suport extern¶

QGIS allows to define a --configpath option that overrides the default path (e.g. ~/.qgis2 under Linux) for user configuration and forces QSettings to use this directory, too. This allows users to e.g. carry a QGIS installation on a flash drive together with all plugins and settings. Also compare with section System Menu.

Date eșantion¶

Ghidul utilizatorului conține exemple bazate pe setul de date exemplu, al QGIS .

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 can either

use GIS data that you already have;
download sample data from at http://download.osgeo.org/qgis/data/qgis_sample_data.zip; or
uninstall QGIS and reinstall with the data download option checked, only if the above solutions are unsuccessful.

For GNU/Linux and Mac OSX 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 ZIP archive from http://download.osgeo.org/qgis/data/qgis_sample_data.zip and unzip the archive on your system. The Alaska dataset includes all GIS data that are used as examples and screenshots in the user guide, and also includes a small GRASS database. The projection for the QGIS sample dataset is Alaska Albers Equal Area with unit 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 graphical frontend 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.

Start QGIS¶

Start QGIS by typing: “QGIS” at a command prompt, or if using precompiled binary, using 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.

Load raster and vector layers from the sample dataset¶

Click on the ^{Load Raster} icon.
Browse to the folder qgis_sample_data/raster/, select the ERDAS Img file landcover.img and click [Open].
If the file is not listed, check if the Filetype combobox at the bottom of the dialog is set on the right type, in this case “Erdas Imagine Images (*.img, *.IMG)”.
Now click on the ^{Load Vector} icon.
File should be selected as Source Type in the new Add Vector Layer dialog. Now click [Browse] to select the vector layer.
Browse to the folder qgis_sample_data/gml/, select “GML” from the filetype combobox, then select the GML file lakes.gml and click [Open], then in Add Vector dialog click [OK].
Zoom in a bit to your favorite area with some lakes.
Double click the lakes layer in the map legend to open the Properties dialog.
Click on the Style menu and select a blue as fill color.
Click on the Labels menu and check the Label this layer with checkbox to enable labeling and choose “NAMES” field as field containing labels.
To improve readability of labels, you can add a white buffer around them, by clicking “Buffer” in the list on the left, checking Draw text buffer and choosing 3 as buffer size.
Click [Apply], check if the result looks good and finally click [OK].

You can see how easy it is to visualize raster and vector layers in QGIS. Let’s move on to the sections that follow to learn more about the available functionality, features and settings and how to use them.

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 application 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 options File QGIS ‣ Quit, or use the shortcut Ctrl+Q.

Command Line Options¶

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 - 2.0.1-Dufour 'Dufour' (exported)
QGIS is a user friendly Open Source Geographic Information System.
    Usage: qgis [OPTION] [FILE]
      options:
        [--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
        [--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
        [--help]                        this text

      FILES:
        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

Tip

Example Using command line arguments

You can start QGIS by specifying one or more data files on the command line. For example, assuming you are in the qgis_sample_data directory, you could start QGIS with a vector layer and a raster file set to load on startup using the following command: qgis ./raster/landcover.img ./gml/lakes.gml

Command line option --snapshot

This option allows you to create a snapshot in PNG format from the current view. This comes in handy when you have a lot of projects and want to generate snapshots from your data.

Currently it generates a PNG-file with 800x600 pixels. This can be adapted using the --width and --height command line arguments. A filename can be added after --snapshot.

Command line option --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. A list of currently supported languages with language code and status is provided at http://hub.qgis.org/wiki/quantum-gis/GUI_Translation_Progress

Command line option --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 loaded described in the given file.

Command line option --extent

To start with a specific map extent use this option. You need to add the bounding box of your extent in the following order separated by a comma:

--extent xmin,ymin,xmax,ymax

Command line option --nologo

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

Command line option --noplugins

If you have trouble at startup with plugins, you can avoid loading them at startup. They will still be available in Plugins Manager after-wards.

Command line option --nocustomization

Using this command line argument existing GUI customization will not be applied at startup.

Command line option --optionspath

You can have multiple configurations and decide which one to use when starting QGIS using this option. See Options to check where does the operating system save the settings files. Presently there is no way to specify in which file where to write the settings, therefore you can create a copy of the original settings file and rename it.

Command line option --configpath

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

Projects¶

The state of your QGIS session is considered a Project. QGIS works on one project at a time. Settings are either considered as being per-project, or as a default for new projects (see Section Options). 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.

The kinds of information saved in a project file include:

Layers added
Layer properties, including symbolization
Projection for the map view
Last viewed extent

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 was updated several times compared to 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

Output¶

There are several ways to generate output from your QGIS session. We have discussed one already in Section Projects 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 or JPG format). A world file with extension PNGW or JPGW saved in the same folder georeferences the image.
Menu option Project ‣ New Print Composer opens a dialog where you can layout and print the current map canvas (see Section Print Composer).