QGIS has been designed with a plugin architecture. This allows new features/functions to be easily added to the application. Many of the features in QGIS are actually implemented as core or external plugins.
- Core Plugins are maintained by the QGIS Development Team and are automatically part of every QGIS distribution. They are written in one of two languages: C++ or Python. More information about core plugins are provided in Section 12.
- External Plugins are currently all written in Python.
They are stored in external repositories and maintained by the individual authors. They can be added to QGIS using the Plugin Installer. More information about external plugins are provided in Section 13.
Managing plugins in general means loading or unloading them using the Plugin Manager. External plugins first need to be installed using the Plugin Installer.
Loading a QGIS Core Plugin
Loading a QGIS Core Plugin is done from the main menu Plugins > mActionShowPluginManagerManage Plugins....<A NAME="24"></A>
The Plugin Manager lists all the available plugins and their status (loaded or unloaded),
including all core plugins and all external plugins that have been added using the Plugin Installer
(see Section external_plugins). Those plugins that are already loaded have a check mark
to the left of their name. Figure <A HREF="#fig:pluginmanager">42</A> shows the Plugin Manager dialog.
To enable a particular plugin, click on the checkbox to the left of the plugin name, and click OK.
When you exit the application, a list of loaded plugins is retained, and the next time
you run QGIS these plugins are automatically loaded.
Loading an external QGIS Plugin
<P> There are two steps required to integrate external plugins into QGIS:
- Download an external plugin from a repository using the Plugin Installer (Section <A HREF="node5.html#sec:python_plugin_installer">11.1.3</A>). The new external plugin will be added to the list of available plugins in the Plugin Manager.
- Load the plugin using the Plugin Manager.
Using the QGIS Python Plugin Installer
<P> In order to download and install an external Python plugin, click the menu Plugins > plugin_installerFetch Python Plugins.... The Plugin Installer window will appear (figure <A HREF="#fig:plugininstaller">43</A>) with the tab Plugins, containing a list of all locally installed Python plugins, as well as plugins available in remote repositories. Each plugin can be either:
- not installed - this means the plugin is available in the repository, but is not installed yet. In order to install it, select the plugin from the list and click the Install plugin button.
- new - this means that the plugin is newly available in the repository.
- installed - this indicates that the plugin is already installed. If it is also available in any repository the Reinstall plugin button will be enabled. If the available version is older than the installed version, the Downgrade plugin button will appear instead.
- upgradeable - this means that the plugin is installed, but there is an updated version available. In this case, the Upgrade plugin button will be enabled.
- invalid - this means that the plugin is installed, but is unavailable or broken. The reason will be explained in the plugin description field.
<P> Plugins tab
<P> To install a plugin, select it from the list and click the Install plugin button. The plugin is installed in its own directory.
- Linux and other unices:
- Mac OS X:
C:\Program Files\QGIS\ python\plugins
C:\Documents and Settings\$USERNAME\ .qgis\python\plugins
<P> If the installation is successful, a confirmation message will appear telling you to go to Plugins > mActionShowPluginManagerManage Plugins... to load the newly installed plugin.
<P> If the installation fails, the reason for the failure will be displayed in a warning dialog. Most often, errors are the result of connection problems and/or missing Python modules. In the former case you will likely need to wait before trying the install again, in the latter case, you should install the missing modules relevant to your operating system prior to using the plugin. For Linux, most required modules should be available via a package manager. For install instructions in Windows visit the module home page. If you are using a proxy, you may need to configure it under Edit > mActionOptionsOptions (Gnome, OSX) or Settings > mActionOptionsOptions (KDE, Windows) on the Proxy tab.
<P> The Uninstall plugin button is enabled only if the selected plugin is installed and is not a core plugin. Note that if you have installed an update to a core plugin, you can uninstall this update with the Uninstall plugin and revert to the version shipped with Quantum GIS. This default version however, cannot be uninstalled.
<P> Repositories tab
<P> The second tab Repositories, contains a list of plugin repositories available for the Plugin Installer. By default, only the QGIS Official Repository is enabled. You can add several user-contributed repositories, including the central QGIS Contributed Repository and other external repositories by clicking the Add 3rd party repositories button. The added repositories contain a large number of useful plugins which are not maintained by the QGIS Development Team. As such, we cannot take any responsibility for them. You can also manage the repository list manually, that is add, remove, and edit the entries. Temporarily disabling a particular repository is possible by clicking the Edit... button.
<P> Options tab
<P> The Options tab is where you can configure the settings of the Plugin Installer. The Check for updates on startup checkbox tells QGIS to automatically look for plugin updates and news. By default, if this feature is enabled all repositories listed and enabled in the Repositories tab are checked for updates each time the program is started. The frequency of update checking can be adjusted using the dropdown menu, and may be adjusted from once a day right up to once a month. If a new plugin or update is available for one of the installed plugins, a notification will appear in the Status Bar. If the checkbox is disabled, looking for updates and news is performed only when the Plugin Installer is manually launched from the menu.
<P> Some internet connections will cause problems when attempting to automatically check for updates. In these cases, a Looking for new plugins... indicator will remain visible in the Status Bar during your entire QGIS session, and may cause a program crash when exiting. In this case please disable the checkbox.
<P> In addition, you may specify the type of plugins that are displayed by the Plugin Installer. Under Allowed plugins, you can specify whether you would like to:
- Only show plugins from the official repository
- Show all plugins except those marked as experimental,
- or Show all plugins, even those marked as experimental.
<P> Data Providers are "special" plugins that provides access to a data store. By default, QGIS supports PostGIS layers and disk-based data stores supported by the GDAL/OGR library (Appendix appdx_ogr). A Data Provider plugin extends the ability of QGIS to use other data sources.
<P> Data Provider plugins are registered automatically by QGIS at startup. They are not managed by the Plugin Manager but used behind the scenes when a data type is added as a layer in QGIS.