4. Características

QGIS offers a wealth of GIS functions, provided by core features and plugins. The locator bar makes it easy to search for functions, datasets and more.

A short summary of six general categories of features and plugins is presented below, followed by first insights into the integrated Python console.

4.1. Visualização de dados

You can view combinations of vector and raster data (in 2D or 3D) in different formats and projections without conversion to an internal or common format. Supported formats include:

  • Spatially-enabled tables and views using PostGIS, SpatiaLite and MS SQL Spatial, Oracle Spatial, vector formats supported by the installed OGR library, including GeoPackage, ESRI Shapefile, MapInfo, SDTS, GML and many more. See section Trabalhando com Informação Vectorial.

  • Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction Library) library, such as GeoTIFF, ERDAS IMG, ArcInfo ASCII GRID, JPEG, PNG and many more. See section Trabalhando com Informação Matricial.

  • Mesh data (TINs and regular grids are supported). See Working with Mesh Data.

  • Vector tiles

  • GRASS raster and vector data from GRASS databases (location/mapset). See section Integração GRASS SIG.

  • Online spatial data served as OGC Web Services, including WMS, WMTS, WCS, WFS, and WFS-T. See section Working with OGC / ISO protocols.

    The QGIS authentication infrastructure helps you manage user/password, certificates and keys for web services and other resources.

  • Spreadsheets (ODS / XLSX)

Temporal data are supported.

4.2. Exploração de dados e compositores de mapas

You can compose maps and interactively explore spatial data with a friendly GUI. The many helpful tools available in the GUI include:

  • QGIS browser

  • Reprojecção On-the-fly

  • 2D and 3D map rendering

  • Gestor BD

  • Print layout

  • Report

  • Painel de Vista Global

  • Marcadores espaciais

  • Ferramentas de anotação

  • Identificar/seleccionar elementos

  • Editar/ver/procurar atributos

  • Data-defined feature labeling

  • Data-defined vector and raster symbology tools

  • Atlas map composition with graticule layers

  • North arrow, scale bar and copyright label for maps

  • Support for saving and restoring projects

4.3. Criar, editar, gerir e exportar dados

You can create, edit, manage and export vector and raster layers in several formats. QGIS offers the following:

  • Vector digitizing tools

  • Ability to create and edit multiple file formats and GRASS vector layers

  • Georeferencer tool to geocode vectors and images

  • GPS tools to import and export GPX format, and convert other GPS formats to GPX or down/upload directly to a GPS unit (on Linux, usb: has been added to list of GPS devices)

  • Support for visualizing and editing OpenStreetMap data

  • Ability to create spatial database tables from files with the DB Manager plugin

  • Tratamento melhorado de tabelas de bases de dados espaciais

  • Tools for managing vector attribute tables

  • Option to save screenshots as georeferenced images

  • DXF-Export tool with enhanced capabilities to export styles and plugins to perform CAD-like functions

4.4. Analyze data

You can perform spatial data analysis on spatial databases and other OGR-supported formats. QGIS currently offers vector analysis, raster analysis, sampling, geoprocessing, geometry and database management tools. You can also use the integrated GRASS tools, which include the complete GRASS functionality of more than 400 modules (see section Integração GRASS SIG). Or, you can work with the Processing plugin, which provides a powerful geospatial analysis framework to call native and third-party algorithms from QGIS, such as GDAL, SAGA, GRASS, OTB, R, and more (see section Introdução). All analysis functions are run in the background, allowing you to continue your work before the processing has finished.

The graphical modeller allows you to combine / chain functions into a complete workflow in an intuitive graphical environment.

4.5. Publicação de mapas na internet

QGIS can be used as a WMS, WMTS, WMS-C, WFS, OAPIF and WFS-T client (see section Working with OGC / ISO protocols), and QGIS Server (see Manual do utilizador QGIS Server) allows you to publish your data through the WMS, WCS, WFS and OAPIF protocols on the Internet using a webserver.

4.6. Extend QGIS functionality through plugins

QGIS can be adapted to your special needs with the extensible plugin architecture and libraries that can be used to create plugins. You can even create new applications with C++ or Python!

4.6.1. Módulos Core

Core plugins include:

  1. DB Manager (exchange, edit and view layers and tables from/to databases; execute SQL queries)

  2. Geometry Checker (check geometries for errors)

  3. Georeferencer GDAL (add projection information to rasters using GDAL)

  4. GPS Tools (load and import GPS data)

  5. GRASS (integrate GRASS GIS)

  6. MetaSearch Catalogue Client (interacting with metadata catalog services supporting the OGC Catalog Service for the Web (CSW) standard)

  7. Offline Editing (allow offline editing and synchronizing with databases)

  8. Processing (the spatial data processing framework for QGIS)

  9. Topology Checker (find topological errors in vector layers)

4.6.2. Módulos Externos Python

QGIS offers a growing number of external Python plugins that are provided by the community. These plugins reside in the official Plugins Repository and can be easily installed using the Python Plugin Installer. See Section The Plugins Dialog.

4.7. Consola Python

For scripting, it is possible to take advantage of an integrated Python console, which can be opened with: Plugins ► Python Console. The console opens as a non-modal utility window. For interaction with the QGIS environment, there is the qgis.utils.iface variable, which is an instance of QgisInterface. This interface provides access to the map canvas, menus, toolbars and other parts of the QGIS application. You can create a script, then drag and drop it into the QGIS window and it will be executed automatically.

For further information about working with the Python console and programming QGIS plugins and applications, please refer to QGIS Python console and Livro de Receitas para Programadores PyQGIS.

4.8. Known Issues

4.8.1. Number of open files limitation

If you are opening a large QGIS project and you are sure that all layers are valid, but some layers are flagged as bad, you are probably faced with this issue. Linux (and other OSs, likewise) has a limit of opened files by process. Resource limits are per-process and inherited. The ulimit command, which is a shell built-in, changes the limits only for the current shell process; the new limit will be inherited by any child processes.

You can see all current ulimit info by typing:

$ ulimit -aS

You can see the current allowed number of opened files per process with the following command on a console:

$ ulimit -Sn

To change the limits for an existing session, you may be able to use something like:

$ ulimit -Sn #number_of_allowed_open_files
$ ulimit -Sn
$ qgis

Alternatively, you can use the newer prlimit utility. More info: https://manpages.ubuntu.com/manpages/latest/man1/prlimit.1.html

To fix it forever

On most Linux systems, resource limits are set on login by the pam_limits module according to the settings contained in /etc/security/limits.conf or /etc/security/limits.d/*.conf. You should be able to edit those files if you have root privilege (also via sudo), but you will need to log in again before any changes take effect.

More info:

https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/ https://linuxaria.com/article/open-files-in-linux