Carson Farmer

For part of a traffic simulation project I am currently working on we need country-wide road network data for Ireland. In the past, getting decent road network data for an area this large was quite a task (not to mention expensive and time consuming), however, with OpenStreetMap we have access to this type of data instantly, and for free! In order to download full country coverage all at once, all I had to do was turn to this extremely useful site, which provides links for daily excerpts of OpenStreetMap data for any country in Europe plus several non-country regions such as the Alps region, as well as select countries outside of Europe. It currently also features special coverage of Haiti.

Now that I have the OSM data downloaded, it should be relatively easy to import it into my PostGIS database using pgRouting and the osm2pgrouting import tool. More to come on this topic once I get things working nicely…

Carson

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.

Read the rest of this entry »

In a recent post, I mentioned that I was testing the stability of clusters generated from a modified network partitioning algorithm using bootstrap resampling techniques. I also mentioned that I was doing this in R, using the very nice foreach package published by REvolution Computing. To show just how nice this package is, below is a minimal example of bootstrapping a network partitioning algorithm which takes advantage of a multicore processor:

Read the rest of this entry »

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.
Read the rest of this entry »

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++).
Read the rest of this entry »

Announcing an opportunity to learn about the leading edge free and open-source technologies for desktop and web-based mapping and data analysis. This is a two day Masterclass focusing on introducing participants to the wonderful world of open source geospatial software. Check out the announcement from the Postgraduate Statistics Centre at Lancaster University.

C

To create a nice bounded Voronoi polygons tessellation of a point layer in R, we need two libraries: sp and deldir. The following function takes a SpatialPointsDataFrame as input, and returns a SpatialPolygonsDataFrame that represents the Voronoi tessellation of the input point layer.
Read the rest of this entry »

One project I’m working on at the moment involves exploring a dynamic extension of the Isomap algorithm for visualising constantly varying real-world road networks. Currently, we are testing out the method on a small scale simulated road network, and most of the original code (written by Laurens van der Maaten, with updates by Alexei Pozdnoukhov), was done in Matlab. Since this work is eventually going to have to run on relatively large datasets, and probably behind the scenes on a server somewhere, we decided that Python was the way to go. The goal therefore was to reproduce the Matlab code using only Python libraries, and the fewer additional libraries required, the better.
Read the rest of this entry »

Two quicks notes to share:

Firstly, please check out this excellent introduction to GIS by Tim Sutton, Otto Dassau, and Marcelle Sutton in partnership with the Chief Directorate for Spatial Planning & Information, Department of Land Affairs, Eastern Cape, South Africa, and the Spatial Information Management Unit, Office of the Premier, Eastern Cape, South Africa. They use QGIS to present some basic GIS concepts and skills, and I particularly like their section on Coordinate Reference Systems.

Secondly, don’t forget to checkout the FOSS4G 2009 Free and open source software for geospatial conference in Sydney in October. There will be loads of excellent presentations and exhibitors, and the atmosphere is always very cool. I will be presenting some software that I’ve been developing for a while now, and will hopefully get a chance to represent QGIS there as well!

C

The other day I was loading a shapefile of approximately 11 million records into a PostGIS database (stay tuned for more on that later) and I wanted to know when shp2pgsql was done. Instead of continually checking the console, I decided to ‘watch’ the process using the *nix command watch. I discovered this handy tool a while ago, and have found that for long running processes, I can use watch to notify me when the process has finished, using the following command:

watch -ben 1 "ps u -C shp2pgsql"
Read the rest of this entry »