PostGIS 2.0 is out and the awesomness continues! You can install PostGIS 2.0 on Ubuntu using packages which is exactly what I am going to show you here. Read on for details on how to get up and running and do your first simple raster analysis!
I’m running a training course next week and will be basing it on the nightly build of QGIS, so I wanted to quickly build an installer for use on the course. I simply ran these commands (starting in a checkout of the Quantum GIS source code).
sudo apt-get install nsis cd ms-windows/osgeo4w ./creatensis.pl qgis-dev cd ..
Now you should see the new installer listed:
1.1K 2012-05-03 13:56 python_plugins.nsh 25K 2012-02-01 09:01 QGIS-Installer.nsi 111M 2012-05-03 14:13 QGIS-OSGeo4W-1.8.0-14615-Setup.exe <-- new installer 9.4K 2011-06-05 00:54 QGIS-Packager.bat 744 2012-02-01 09:01 quickpackage.sh 11K 2011-06-05 00:54 README.html 7.1K 2011-06-05 00:54 ui.nsh
Be aware that the process takes some time and doesn’t really show much on the screen other than an dump of the nsis file created while it is happening. Just sit tight and wait for the command line prompt to return to you.
Its been two weeks now since I returned from the QGIS Hackfest in Lyond, France, but I haven’t had the time to write up my experiences yet….until now. Read on for more!
During the Zurich QGIS hackfest we had some extended discussions about migrating our documentation away from LaTeX to sphinx because the latter offers a more approachable syntax for casual documentation writers and has good support for internationalisation via gettext. This week I am going to our first 2012 QGIS hackfest (to be held in Lyon, France) and we will be spending some time and effort to move forward with the migration to sphinx. In order to get familiar with sphinx, I have slowly been moving my own documentation work from txt2tags (which I love for its simplicity, but it is not great for complex documents that need interdocument references) to sphinx (which is a little more complex but has many more bells and whistles). Sphinx provides a number of themes ‘out of the box’ for generated html content, but I don’t really like any of them much and I want my stuff to look a little more unique. So I have dipped my toes a little into the waters of sphinx theme creation. This weekend I decided to make my efforts public. There are still a number of layout issues I want to address (mainly in the TOC sidebar), and I want to add some more explicit markup for various sphinx constructs, but what I have is already usable and hopefully interesting for others to try out. Here is a little screenshot of what the theme looks like:
You can download the theme from its github project page (https://github.com/timlinux/linfiniti-sphinx-theme) – the accompanying README should give you enough info to get started with it. I am hoping that we can use a variant of this theme for the QGIS project documentation too. I look forward to any patches to make the theme better any of you html/css gurus out there may have to offer!
You probably looked at the GDAL Tools (under the raster menu in QGIS) and blissfully ignored that ‘Creation Options’ panel that appears near the bottom of some dialogs. This is definately a power user feature, but a very handy one. In this quick article I will show you how to compress the rasters you create (bits are a valuable resource right?) by adding in some options there.
One of the really cool features in QGIS that doesn’t get much press is the ability to run actions based on a feature selection. Under 1.7.4 this works by using the identify tool and then choosing an action from the action list in the identified feature(s) attributes. A new improvement in QGIS master (and should be in the upcoming 1.8) added by Giuseppe Sucameli adds an action map tool which allows you to click on any feature and run a related action. Actions can include tokens referencing feature attributes so that you can, for example, display a picture related to a feature using an external program, passing the program a file name taken from an attribute of the selected feature. Most people immediately grasp that you can just add the name of an external app e.g. firefox and pass attributes as parameters. There are some shortcomings with this approach in that it adds an unknowable dependency – will the end-user have the software required to execute the action on their system? Its easy to forget that QGIS sits on top of the incredibly powerful and versatile Qt4 library, and all that goodness is just a heartbeat away with a python line or two. Also, in QGIS actions can be arbitrary, tokenised (i.e. using variable information based on the contents of a field attribute) python commands! In this short article I will demonstrate how to use an a python action to show a web page. The url will be generated based on an attribute value and best of all, it requires no browser on the user’s system since it uses the Qt4 QWebView class (which is a webkit based html widget) to display the content in a pop up window.
Having a good world dataset is kind of essential for most GIS users to have as a standard reference dataset, give context to maps and so on. Anita Graser’s recent blog post about the Natural Earth Data project added another nice dataset to my world dataset collection. The Natural Earth Data set (I got the ‘full’ one) is provided as shapefiles. Of course as a PostGIS fan I’d rather have these in my geospatial database, so I wrote a one liner in bash to load all the datasets.
I often do this – I work away on my master branch and suddenly realise ‘damn I should have branched before I started this’. Usually this happens because what I think will be a trivial change snowballs into something much more sweeping. I thought I would record here how to deal with situations like this by retroactively creating a branch and rolling master back to a previous state. Note: backup your data first and this is only ideal if you haven’t pushed changes to a remote repo yet.
Here is a quick handy tip if you are using GIT and want to be able to quickly diff or checkout the code base from a week, month etc. ago.
Some time ago I spent at least a day trying to find a good quality, free world political borders and coastlines dataset. Each product I found had some limitation – incomplete coverage or poor resolution. Today by happenstance a client pointed me to quite a good one.