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Noțiuni de bază

This chapter gives a quick overview of installing QGIS, some sample data from the QGIS web page, and running a first and simple session visualizing raster and vector layers.

Instalare

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.

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 them online at http://htmlpreview.github.io/?https://raw.github.com/qgis/QGIS/master/doc/INSTALL.html

Instalarea pe un suport extern

QGIS allows you to define a --configpath option that overrides the default path for user configuration (e.g., ~/.qgis2 under Linux) and forces QSettings to use this directory, too. This allows you to, for instance, carry a QGIS installation on a flash drive together with all plugins and settings. See section Meniul Sistemului for additional information.

Date eșantion

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

win 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:

nix osx 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.

Start QGIS

  • nix Start QGIS by typing “QGIS” at a command prompt, or if using a precompiled binary, by using the Applications menu.
  • win Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.
  • osx Double click the icon in your Applications folder.

Load raster and vector layers from the sample dataset

  1. Click on the mActionAddRasterLayer Add Raster Layer icon.

  2. Răsfoiți folderul qgis_sample_data/raster/, selectând fișierul landcover.img și făcând clic pe [Deschidere].

  3. If the file is not listed, check if the Files of type selectstring combo box at the bottom of the dialog is set on the right type, in this case “Erdas Imagine Images (*.img, *.IMG)”.
  4. Now click on the mActionAddOgrLayer Add Vector Layer icon.
  5. radiobuttonon File should be selected as Source Type in the new Add vector layer dialog. Now click [Browse] to select the vector layer.
  6. Browse to the folder qgis_sample_data/gml/, select ‘Geography Markup Language [GML] [OGR] (.gml,.GML)’ from the Filter selectstring combo box, then select the GML file lakes.gml and click [Open]. In the Add vector layer dialog, click [OK]. The Coordinate Reference System Selector dialog opens with NAD27 / Alaska Alberts selected, click [OK].
  7. Zoom in a bit to your favorite area with some lakes.

  8. Dublu clic pe stratul lakes din legenda hărții pentru a deschide fereastra de dialog Properties.

  9. Clic pe fila Stil, apoi selectați albastru ca și culoare de umplere.

  10. Click on the Labels tab and check the checkbox Label this layer with checkbox to enable labeling. Choose the “NAMES” field as the field containing labels.
  11. To improve readability of labels, you can add a white buffer around them by clicking “Buffer” in the list on the left, checking checkbox Draw text buffer and choosing 3 as buffer size.

  12. Clic [Aplicare]. Verificați dacă rezultatul arată bine, iar apoi faceți clic pe [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.

  • nix 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.
  • win Start QGIS using the Start menu or desktop shortcut, or double click on a QGIS project file.
  • osx 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 nix win File osx QGIS ‣ Quit, or use the shortcut Ctrl+Q.

Opțiunile liniei de comandă

nix 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

Tip

Exemplu de folosire a argumentelor în linia de comandă

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

Opțiunea liniei de comandă --snapshot

Această opțiune vă permite să creați o captură, în format PNG, a vizualizării curente. Acest lucru este foarte util atunci când aveți o mulțime de proiecte și doriți să generați capturi din datele proprii.

În prezent, se generează un fișier PNG cu 800x600 pixeli. Acest lucru se poate face din linia de comandă utilizând argumentele --width and --height. Un nume de fișier poate fi adăugat după --snapshot.

Opțiunea liniei de comandă --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.

Opțiunea liniei de comandă --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.

Opțiunea liniei de comandă --extent

Pentru a începe cu o extindere de hartă specifică, folosiți această opțiune. Trebuie să adăugați valorile casetei de încadrare, separate prin virgulă, în ordinea următoare:

--extent xmin,ymin,xmax,ymax

Opțiunea liniei de comandă --nologo

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

Opțiunea liniei de comandă --noplugins

Dacă aveți probleme la pornire cu plugin-urile, puteți evita încărcarea lor la lansare, folosind această opțiune. Acestea vor fi în continuare disponibile din Managerul de Plugin-uri.

Opțiunea liniei de comandă --customizationfile

Folosind acest argument în linia de comandă, puteți defini un fișier de personalizare GUI, care va fi utilizat la pornire.

Opțiunea liniei de comandă --nocustomization

Folosind acest argument în linia de comandă, personalizarea existentă a GUI-ului nu va fi aplicată la pornire.

Opțiunea liniei de comandă --optionspath

You can have multiple configurations and decide which one to use when starting QGIS with this option. See Opţiuni 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/

Opțiunea liniei de comandă --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.

Opțiunea liniei de comandă --code

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

De exemplu, atunci când aveți un fișier Python numit load_alaska.py, cu următorul cuprins:

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

Proiecte

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 Opţiuni). QGIS can save the state of your workspace into a project file using the menu options Project ‣ mActionFileSave Save or Project ‣ mActionFileSaveAs Save As....

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

If you wish to clear your session and start fresh, choose Project ‣ mActionFileNew 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.

Tipurile de informații salvate într-un fișier proiect includ:

  • Straturile adăugate

  • Straturile care pot fi interogate

  • Proprietățile stratului, inclusiv simbolizarea și stilurile

  • Proiecția pentru vizualizarea hărții

  • Ultima extindere vizualizată

  • Compozitoare de Hărți

  • Elementele Compozitorului de Hărți cu setări

  • Setările Atlasului Compozitorului de Hărți

  • Setări de digitizare

  • Relațiie Tabelei

  • Macrocomenzile Proiectului

  • Stiluri implicite ale proiectului

  • Setările Plugin-urilor

  • Setările QGIS server din fila de setări OWS a proprietăților proiectului

  • Interogările stocate în 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:

  • checkbox Prompt to save project and data source changes when required
  • checkbox 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 ~.

Rezultat

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

  • Menu option Project ‣ mActionSaveMapAsImage 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 ‣ mActionNewComposer New Print Composer opens a dialog where you can layout and print the current map canvas (see section Compozitorul de Hărți).