1. 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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  2. 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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  5. 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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  6. Speeding up geoprocessing in QGIS

    Thu 01 April 2010
    cfarmer

    Last night I had an uncontrollable urge to make geopoprocessing in QGIS better, faster and more fun! I had come across a couple of posts (here, here) on the idea of a cascaded union operation, and since it has recently been added to GEOS (which QGIS uses for its geometry operations), I thought I’d give a much needed boost to the fTools union tool and related functions.

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  7. QGIS developer meeting update

    Wed 11 November 2009
    cfarmer

    Last week I attended the 2009 QGIS Developers Meeting in Vienna, Austria. We all had a really good time, met many new people, and actually got a lot done in the process. There have been updates about the meeting (hackfest) on the QGIS blog, and Tim Sutton has written a few words about our progress as well. I’m not going to repeat what others have said, but I would like to give a quick update on the work that I was doing at the meeting, and show off the new geoprocessing features now available to all QGIS developers (Python and C++).

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  8. Remote Sensing of Environment paper published

    Tue 06 October 2009
    cfarmer

    My latest article, “Identification of snow cover regimes through spatial and temporal clustering of satellite microwave brightness temperatures”, has recently been published on-line, with the journalRemote Sensing of Environment. For now, UPDATE: The article can be cited as:

    Farmer, C. J. Q., Nelson, T. A., Wulder, M.A. and Derksen, C. (2010). Identification of snow cover regimes through spatial and temporal clustering of satellite microwave brightness temperatures, Remote Sensing of Environment, 114 (1): 199-210.

    If you would like a copy, but do not have access to the article, please email me and I can forward you a PDF version.

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