Blog

PostgreSQL back end solution for quality assurance and data archive

Did you know that the possibilities to make a full QGIS back end solution for quality assurance and archiving in PostgreSQL are immense? SQL has it’s well known limitations, but with a little bit creativity you can make quite nice solutions just using triggers and rules. In this post I’ll explain what we did lately based on a project with a customer. He needed to assure the consistency of data but still give his employees the possibility Read more

By Dave Signer, ago

Interlis translation

Lately, I have been confronted with the need of translating Interlis files (from French to German) to use queries originally developed for German data. I decided to create an automated convertor for Interlis (version 1) Transfer Format files (.ITF) based on the existing cadastral data model from the Swiss confederation (DM01AVCH). The ILI model file conversion has been achieved manually once. This was quite simple since the used model is an extension with little to Read more

By Mario Baranzini, ago

Best practices for writing Python QGIS Expression Functions

Recently there have been some questions and discussions about python based expression functions and how parameters like usesGeometry  need to be used. So I thought I’d quickly write down how this works. There is some intelligence If the geometry or a column is passed in as a parameter you do not need to request it manually, you can even specify explicitly that you do not require the geometry or a column here. @qgsfunction(args=’auto’, group=’Custom’, usesGeometry=False, referencedColumns=[]) def Read more

By Matthias Kuhn, ago

QGIS Expressions Engine: Performance boost

Expressions in QGIS are more and more widely used for all kinds of purposes. For example the recently introduced geometry generators allow drawing awesome effects with modified feature geometries on the fly. The last days at the QGIS developer meeting 2017, I spent some time looking into and improving the performance for expressions. This was something that was on my todo list for a while but I never got around to working on it. Short Read more

By Matthias Kuhn, ago

QGIS2 compatibility plugin

Lately I’ve been spending time porting a bigger plugin from QGIS 2.8 to 3 while maintaining 2.8 compatibility. You can find it at https://github.com/opengisch/qgis2compat/ and https://plugins.qgis.org/plugins/qgis2compat/ One code to rule them all. My target was to have to edit the source code as little as possible to simulate a lazy or busy coder that has to upgrade his/her plugins. Lots of work has already gone into 2.14 to support PyQt 4 and 5 with the Read more

By Marco Bernasocchi, ago

Updating PyQt signals that use lambda in QGIS with 2to3

Just for the sake of documenting things, when running qgis 2to3 on a plugin I encountered a tricky situation regarding signals. MYQGISDIR/scripts/2to3 -f signals -w my/plugin/path The original code: extra_arg = “my test argument” QObject.connect( action, SIGNAL( “triggered()”), lambda extra_arg=my_arg: show_extra_arg(extra_arg)) def do_load_project(extra_arg): print extra_arg # “my test argument” The generated code: extra_arg = “test_arg” action.triggered.connect( lambda extra_arg=my_arg: show_extra_arg(extra_arg)) def do_load_project(extra_arg): print extra_arg # False so in do_load_project we get False instead of “my test Read more

By Marco Bernasocchi, ago

QGIS: Qt5 and Python3 migration, current state

Behind the scenes a lot has happened to get ready for Qt5 and Python3. On the same codebase that is becoming the next release QGIS 2.16. This is really a great thing since we can focus work on a single master branch and I’m very happy that we got so far with this approach already. Testing At OPENGIS.ch we have put a huge effort into getting the Travis CI test infrastructure to test our code with Qt5 Read more

By Matthias Kuhn, ago

Prepare your plugins for QGIS 3

QGIS 3 is not yet there and there is still plenty of time to prepare and migrate. But I thought I would give some advice about things that you can keep in mind while working on your plugins to make your life easier when you will have to actually do the migration. It’s mostly about making your code prepared for Python 3 and PyQt5. Do not use star imports Don’t do from PyQt4.QtCore import * Read more

By Matthias Kuhn, ago

Increasing the stability of processing algorithms

Processing just got a new testing framework to improve the long-term stability of this important plugin. And you can help to improve it, even if you are not a software developer! This is yet another piece in our never-stopping crusade to improve the stability and quality of the best desktop GIS on the market. Processing You probably know processing. If you don’t: processing is the number one plugin to enable after every QGIS installation. It offers a Read more

By Matthias Kuhn, ago