So at least once a week I’m getting a phone call or an email on QGIS. This one was pretty awesome and it pointed out I need to cover geoprocessing in Class in a little more detail.
The question was “In our transition out of ESRI products we hit a snag. We want to merge or dissolve 925,000 polygons on an attribute. QGIS Hangs. Arcmap Completes it. Why doesn’t QGIS complete the task?” They took an abbreviated version of the QGIS class at FOSS4GNA back in the spring.
I thought about it and started running some tests. You can dissolve/merge the data two ways in QGIS and you can do it in PostGIS. ArcGIS people tend to get hung up on this as you have one way in ArcMap. So I listed out the three ways from Simplest to hardest (Finals: GRASS won for speediest answer, PostGIS won for cleanest answer, QGIS won for simplest answer).
If you think of Geoprocessing in QGIS you actually can get two “correct” answers. One deals with FWTools and one deals with the Toolbox. Yes – both QGIS and ESRI have Toolboxes. Before QGIS 2.14 you had FWtools in the vector menu. That software was there from the beginning or close and is derived from http://fwtools.maptools.org/ (FW is Frank Warmerdam). Sextante started making an appearance sometime in 2.0 as a plugin. Sextante combined a lot of tools into one menu system. Eventually it made it was as a part of the core release and became the Processing Toolbox. FWTools started getting out of date. Somewhere in 2.12 or earlier it was decided to replace FWTOOls with the Processing Toolbox
The fun is at the 2.14 release. It’s a Long term release. If you’re running an earlier version you will still see FWTools. As I’m sitting here looking at 2.14.6 It appears FWTools is gone. In 2.16 the vector menu at the top has regained all the functionality you remember from 2.1 or early versions of 2.14 – it just looks different. You now have unified processing tools in 2.16. No FWTools.
Back to the problem. The student from class was running 2.14.2. They still had FWTools and “googling” pointed them to the answer being in the FWTools toolset under vector. The merge didn’t work. The Dissolve in the processing toolbox finished in about 20 minutes. So my followup email in a few days will be – Did it work and do you feel better? Are you really dropping the other stuff? I’ve yet to suggest people ditch their commercial GIS system. I do have more and more people starting from scratch and going open source. It’s interesting.
The moral to the story – QGIS is evolving. If you decide “I’m going to sit at this one version for a year” you are missing out. You should at least think of upgrading like you would an ESRI Service pack. If you are on 2.14 – upgrade to the current LTR (Long Term Release) release (which is 2.14.6 as of this date of posting). If you want to live on the edge – go with 2.16 (I did but I’m weird that way).