Category: QGIS

QGIS Multi Ring Buffer Plugin Version 1

After about 3 years of existing. I am releasing version 1 of the Multi Ring Buffer Plugin.

QGIS plugin repository.

With version 1 comes a few new features:

  • Ability to choose the layer to buffer after launching the plugin
  • Ability to supply buffer distances as comma separated text string
  • Ability to make non-doughnut buffers

    • Doughnut buffer:

    Non-doughnut buffer (regular):

    Works either in a sequential manner by buffering the resulting buffer and differencing the previous buffer, or a central manner by buffering the original feature with different distances. Also by default the buffer dissolves the features before buffering.

    Dissolving makes adjacent features behave in a better manner without overlapping buffers. The QGIS buffer feature has the logic behind this.

    Post:

    Buffering methodology

    Known issues:

    Help Guide

    Code:

    GitHub Code Base

    Issues and bug tracker:

    GitHub Issues

    Updating A Plugin From QGIS 2 to QGIS 3

    I have two plugins in the QGIS plugin repository, and with the release of QGIS 3 looming it was time to upgrade them for QGIS 3.

    There is a short guide by the QGIS dev team that is a good starting point at:
    https://github.com/qgis/QGIS/wiki/Plugin-migration-to-QGIS-3

    But I had not done any development on these plugins for a while so a more step by step guide was useful, so hopefully, write the guide for the first plugin and follow it step by step for the second.

    I am working on Windows, with OSGeo4W.

    Before we start we will need to insure a couple of extras are installed through the OSGeo4w Installer:
    Desktop:
    qgis-dev
    Libs:
    python-future

    Assuming GitHUB is the repo.
    In git shell:

    git clone https://github.com/HeikkiVesanto/QGIS_Multi_Ring_Buffer.git

    There is a conversion script for QGIS plugins provided by the QGIS devs in the main repo.

    UPDATE:
    The qgis2to3 packages can be found on pip now:

    https://github.com/opengisch/qgis2to3/

    We can download just the scripts folder using the following link:
    https://minhaskamal.github.io/DownGit/#/home?url=https://github.com/qgis/QGIS/tree/master/scripts

    Extract that into a location of your choice.

    Then we can run the 2to3 script from the OSGeo4W console (cd to the folder you extracted the script to):

    python 2to3 C:\path_to_plugin\QGIS_Multi_Ring_Buffer

    This will print out changes that need to be made to convert from QGIS2 to QGIS3.

    My first run resulted in many lines of:

    RefactoringTool: Line 31: could not convert: from PyQt4.QtCore import *
RefactoringTool: Cannot handle star imports.

    So my plugins line of:

    from PyQt4.QtCore import *

    Was impossible to convert with the tool, since I was not 100% sure what I needed from the QtCore library (I was young when I wrote the plugin). I commented out the line for the plugin in QGIS 2.8, booted up QGIS 2.8 and tried running the plugin.

    So python errors:
    NameError: global name ‘QVariant’ is not defined
    NameError: global name ‘Qt’ is not defined
    Later. I ended up expanding my other import from QtCore to:

    from PyQt4.QtCore import QSettings, QTranslator, qVersion, QCoreApplication, QVariant, Qt

    Running the 2to3 script again looked ok, with a number of changes required. These changes can be applied with –w flag:

    python 2to3 C:\path_to_plugin\QGIS_Multi_Ring_Buffer -w

    For the next step I booted up my favourite IDE PyCharm. I created a bat file that launched PyCharm with the QGIS dev environmental variables. So copying the “python-qgis-dev.bat” file from:

    I changed the final line of:

    "%PYTHONHOME%\python" %*

    To:

    start /d "C:\Program Files\JetBrains\PyCharm Community Edition 2017.2.1\bin\" pycharm64.exe

    Then from File> Settings> Project:> Project Interpreter> Set to “C:\OSGeo4W64\apps\Python36\python.exe”

    It takes a while to update the interpreter.

    I only had 2 errors, both for:
    QgsMapLayerRegistry.instance().addMapLayer(vl)

    There is a list of API breaks between QGIS 2 and QGIS 3 at:
    https://qgis.org/api/api_break.html

    Looks like QgsMapLayerRegistry was moved to QgsProject. So I edit it to:

    QgsProject.instance().addMapLayer(vl)

    Then we can edit the metadata.txt to QGIS 3:
    qgisMinimumVersion=3.0

    And increase the version number.

    Then we need to recompile the icon and ui for Python3 and QT5.

    I was struggling a bit with the environmental variables to get it working, and ended up using a great batch script form StackExchange:
    https://gis.stackexchange.com/questions/260743/how-to-compile-qtdesigner-user-interface-ui-and-resource-qrc-files-with-qg

    @ECHO OFF

set OSGEO4W_ROOT=C:\OSGeo4W64

set PATH=%OSGEO4W_ROOT%\bin;%PATH%
set PATH=%PATH%;%OSGEO4W_ROOT%\apps\qgis\bin

@echo off
call "%OSGEO4W_ROOT%\bin\o4w_env.bat"
call "%OSGEO4W_ROOT%\bin\qt5_env.bat"
call "%OSGEO4W_ROOT%\bin\py3_env.bat"
@echo off
path %OSGEO4W_ROOT%\apps\qgis-dev\bin;%OSGEO4W_ROOT%\apps\grass\grass-7.2.2\lib;%OSGEO4W_ROOT%\apps\grass\grass-7.2.2\bin;%PATH%

cd /d %~dp0

@ECHO ON
::Ui Compilation
call pyuic5 multi_ring_buffer_dialog_base.ui -o multi_ring_buffer_dialog_base.py          

::Resources
call pyrcc5 resources.qrc -o resources_rc.py

@ECHO OFF
GOTO END

:ERROR
   echo "Failed!"
   set ERRORLEVEL=%ERRORLEVEL%
   pause

:END
@ECHO ON

    So create the .bat file and run it in the folder of you plugin (editing where needed). Note: Your resources_rc may be called resource_rc or something slightly different.

    Move the plugin folder to:
    C:\\Users\\USERNAME\\AppData\\Roaming\\QGIS\\QGIS3\\profiles\\default\\python\\plugins\\

    Boot up QGIS2.99/3.

    I had a few more issues.

    It seems QGIS 3 deals with the icon slightly differently.

    icon_rc.py is no longer needed, and it seems was not used on my other plugin either.

    So I removed the reference to it in the main python script:
    from . import icon_rc

    I still had some errors.

    AttributeError: module ‘qgis.PyQt.QtGui’ has no attribute ‘QDialog’

    It seems QDialog has moved to PyQt.QtWidgets.

    So in my multi_ring_buffer_dialog.py file I needed to change some lines:

    Add:

    from qgis.PyQt.QtWidgets import QDialog, QDialogButtonBox

    Change:
    QtGui.QDialog
    to:
    QDialog
    In the two instances in that file.

    Working plugin!

    Commit the changes back to the repo. Cd to the directory in git shell.

    git add -A
git commit –m “Updated for QGIS 3”
git push

    Zip the plugin up.
    Upload to https://plugins.qgis.org/plugins/

    Second plugin:
    Same issue with import *
    1 error with QgsMapLayerRegistry
    My resources_rc file was called resource_rc so the batch script needed to be edited to:
    call pyrcc5 resources.qrc -o resource_rc.py
    Same issues with QtGui.QDialog

    Now time for some improvements.