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How to filter features in QGIS using the graphical processing modeler

This article describes a new algorithm for the processing modeler called feature filter algorithm. If you are already familiar with ETL concepts and the graphical modeler, you can directly jump to the section the feature filter algorithm. Building workflows for repetitive tasks When building workflows for simple or complex geodata infrastructures, one of the most common tasks one encounters is to extract some of the features and copy them to another destination. Sometimes they need Read more…

By Matthias Kuhn, ago

Marco becomes QGIS.org Co-chair

We are very proud to announce that one of our founders and directors Marco Bernasocchi was elected as QGIS.org project steering committee (PSC) co-chair. With over 10 years of involvement with QGIS (he started working with QGIS 0.6) Marco will serve for the next two years as one of the board members of the QGIS.org association. He is excited to get the chance to work together with the PSC and the fantastic QGIS community to Read more…

By Matthias Kuhn, ago

Porting QGIS plugins to API v3 – Strategy and tools

The Release of QGIS 3.0 was a great success and with the first LTR (3.4) scheduled for release this fall, it is now the perfect time to port your plugins to the new API. QGIS 3.0 is the first major release since September 2013 when QGIS 2.0 was released. During the release cycles of all 2.x releases, the QGIS Python API remained stable. This means that a plugin or script meant to be used in Read more…

By Marco Bernasocchi, ago

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