1. Python Resources for QGIS Users

   Tue 18 March 2014

   cfarmer

   There’s a discussion thread on the QGIS LinkedIn Group page about Python tutorials and resources. There were a few good suggestions, so I thought I’d share these with others. It starts with a very common question from a GIS (or any software that supports scripting) user:

   I’m a real ‘end-user’ of qgis and I want to improve my skills a little… I’ve found many python tutorials online but I don’t know which are any good. Can anyone point me to some good resources?

   The responses were useful, but not exhaustive:

   • The PyQGIS Programmer’s Guide ...

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2. ftools is dead… long live ftools!

   Tue 15 October 2013

   cfarmer

   I recently decided to drop ftools.ca, since I hadn’t updated it in a very long time, and it was really just costing me money to keep a ‘dead’ website up and running. Additionally, with the new QGIS plugin infrastructure, hosting my own plugins (the website’s primary purpose) was no longer needed. The site has served me well for many years, and really helped get fTools (the plugin) into the QGIS core codebase. The website has served its purpose, and now that I have very little involvement with fTools and the QGIS Processing Toolbox that is poised to replace it, I’m moving on: ftools.ca is dead, long live ftools.ca!

   However, now that QGIS 2.0 has rolled out, it seems that at least one part of ftools.ca is missed: my old cartogram plugin. If I have some spare time, I’ll try to update the plugin to the latest and greatest QGIS 2.0 standards and upload it to the new QGIS plugins system. In the mean time, for those out there who would like to use it right away, you can get the original code from here or grab it from github. In fact, if someone is able and willing, they can grab the code from github, update it for QGIS 2.0, and submit a pull request which I will (more than likely) happily accept.

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3. manageR and rpy2 installation problems

   Sat 06 October 2012

   cfarmer

   Unfortunately, I haven’t had much time recently to update or work on manageR, but I’m hoping that will change in the next few months… Having said that, there are quite a few people out there that have been having trouble installing manageR (and the required rpy2) on their system to get things working at all! I have had some individuals provide possible fixes and suggestions on how to get things working properly on various platforms, and I’m going to use this post to amalgamate them, and hopefully create a one stop post for all your rpy2 and manageR needs. I’m also hoping that people will post potential fixes in the comments to help others with more specific problems?

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4. Adding direct editing of geometry fields in QGIS

   Sat 12 March 2011

   cfarmer

   Being able to add/remove attributes isn’t actually a very new feature for QGIS at this point. However, to date non of the fTools functions (Vector menu) have taken advantage of this capability. If a tool needed to create a new field in the input vector layer, it simply wrote a new version of the vector layer to disk with the additional fields added. There have been several requests to allow some tools to add/update attributes directly on the input layers, so I went ahead and created a script to test this functionality out. I’ve provided a copy here for anyone who would like to test it out before I add it to QGIS permanently. Basically, the script will replace/update three of the Vector menu tools, including Analysis \> Sum line lengths, Analysis \> Points in polygon, and Geometry tools \> Add/Export geometry info.

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5. pgRouting, OpenStreetMap, and QGIS

   Thu 14 October 2010

   cfarmer

   I mentioned a few posts back that there was a great resource for downloading OpenStreetMap data, and that it was relatively easy to import osm data into PostgreSQL/PostGIS for use with pgRouting to calculate shortest paths and various other network-based operations. In this post, I’ll outline the steps required to get all this up and going, and provide a quick example to show how this can be combined with QGIS to visualise the computed shortest path directly.

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6. Adding a bit of class(ification) to QGIS…

   Wed 29 September 2010

   cfarmer

   In my last post, I implemented several classification algorithms for quantitative data which could be used directly from the Python console in QGIS. While this was a handy addition to my PyQGIS toolkit, it wasn’t quite handy enough for me, so I decided to (re)implement the same algorithms in C++ so that they could be added directly to the QGIS API. Before I did that however, I wanted to fix a few issues, and speed things up a bit, particularly for the Jenks Natural Breaks algorithm, which can be quite slow for large datasets.

   After porting everything over ...

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7. Playing around with classification algorithms: Python and QGIS

   Thu 23 September 2010

   cfarmer

   Data visualization is part of my everyday work-flow. More often than not, I’m playing around with my data in a GIS to tease out interesting or informative spatial patterns, or to ensure that I’m getting the results that I’m expecting. As a result, I am constantly trying out different classification schemes to help me generalize spatial patterns, highlight outliers and/or patterns, or just plain mess around with my data.

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8. PostGIS ‘select’ statement as vector layer in QGIS

   Tue 27 April 2010

   cfarmer

   Several colleagues of mine have asked whether it is possible to visualise the results of a SELECT statement on a PostGIS database that returns spatial data in QGIS. In other words, can we map the results of something like:

   SELECT id, st_union(the_geom) FROM spatial_table GROUP BY id;
   

   My usual answer to this in the past has been “not yet…”, but now thanks to Giuseppe Sucameli and Jürgen E. Fischer, the answer is a resounding “yes!”. A recent patch to QGIS trunk now makes custom Postgres queries possible via the postgres data provider.

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