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Getting Ready for Quantum GIS Plugin Development

Quantum GIS (QGIS) is a desktop GIS application that can be extended with Python plugins. We are going to use Plugin Builder from within QGIS. Plugin Builder is not installed by default. Start QGIS and follow these steps to install Plugin Builder:


Installing Plugin Builder

  1. Select Plugins->Fetch Python Plugins. A QGIS Python Plugin Installer dialog box will open.
  2. Select Repositories tab.
  3. Click on Add 3rd party repositories button. A confirmation dialog box will appear. Click Ok. Another dialog box will appear to fetch the repositories. The dialog box will close itself.
  4. Select Plugins tab.
  5. Select Plugin Builder from the list.
  6. Click on Install Plugin button.

Plugin Builder menu will appear in Plugins menu. Select Plugins->Plugin Builder->Plugin Builder to start the Plugin Builder. A QGIS Plugin Builder dialog box will appear.


Generating QGIS Python plugin file set


We use the Plugin Builder to generate a basic file set for our QGIS Python plugin. Fill in the QGIS Plugin Builder dialog box with our plugin details. Click Ok. Select the directory where we want to keep our plugin. The Plugin Builder will generate the files in the directory we chose and will give us the following instruction (assuming that we name our plugin myplugin):

  1. Copy the entire directory containing your new plugin to the QGIS plugin directory
  2. Compile the ui file using pyuic4 (refer to Compiling our plugin section below) 
  3. Compile the resources file using pyrcc4 (refer to Compiling our plugin section below) 
  4. Test the plugin by enabling it in the QGIS plugin manager (refer to Tesing our plugin section below)
  5. Customize it by editing the implementation file myplugin.py
  6. Create your own custom icon, replacing the default icon.png
  7. Modify your user interface by opening ui_myplugin.ui in Qt Designer (don't forget to compile it with pyuic4 after changing it)
  8. You can use the Makefile to compile your Ui and resource files when you make changes. This requires GNU make (gmake)

Compiling our plugin


See Setting Up PyScripter for Quantum GIS on how to open a command prompt window that we can use to compile our plugin.


1. Compiling resources.qrc into resources.py

pyrcc4 -o resources.py resources.qrc
2. Compiling ui_myplugin.ui into ui_myplugin.py

pyuic4 -o ui_myplugin.py ui_myplugin.ui
We can design our user interface (ui) using Qt Designer which is bundled in Qt SDK. Open ui_myplugin.ui from within Qt Designer. Once we make a ui change we need to recompile it with pyuic4.


Testing our plugin

  1. Compile resources.grc and ui_myplugin.ui.
  2. Select Plugins->Manage Plugins. A QGIS Plugin Manager dialog box will appear.
  3. Select our plugin from the list. Click Ok to install it.
  4. Our plugin menu will appear in Plugins menu. Click on it.

Note: Each time we make changes to our plugin we need to restart QGIS.

Comments

  1. AnonymousNovember 4, 2012 at 7:46 PM

    Wish I'd found this POST earlier. THANKS!!

    Only problem was I had to edit myplugin.py line 27 to change "import resources_rc" to "import resources" (i.e. remove the _rc on import of resources.

    ReplyDelete

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