Archive for the ‘opensource’ tag
OpenSource Upgrades
Moving to new versions in OpenSource has in the past been like playing Russian roulette. Just now clicking on “Upgrade to WordPress 3.0″ I thought would lead to a greater understanding of the database schema, template inconsistencies, and plug-in idiosynchrocies of WordPress as I met an inevitable “Upgrade Failed. Please see log for details” message.
But no! Five seconds later, all was successful, and everything looked as before. There have been numerous bug fixes and improvements, but after a brief look through the list I didn’t see any “killer” new features.
In the world of GIS however there are a number of important new versions coming up this summer.
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Stack Overflow & OSGeo
Stack Overflow, as most developers will already know, is a question and answer site for programmers. It’s perfect for mainstream development questions in any programming language, and has also become the support site of choice for some newer programming communities such as Android developers. 
It can also be used as a barometer to see which current open source GIS projects have gained traction in the mainstream programming world. I took the full list of OSGeo projects from http://www.osgeo.org/ and ran queries on the site to see how many questions there were for each project. The results are as follows (as of May 2010):
Automated WMS Reports
This post details how the WMS GetCapabilities request can be used to create an automated report listing all the map layers available from a WMS server. The final sample page can be seen here.
The GetCapabilities Request
Web Mapping Services (WMS) is an open standard that all major GIS vendors implement in their server software (for example see the ESRI documentation). As a result applications built on these services are able to easily switch from one software package to another – allowing separation of code that allows for easier maintenance and reuse.
The GetCapabilities is one of three requests in the WMS specification. It “returns service-level metadata, which is a description of the service’s information content and acceptable request parameters.”
After eventually being able to see the results of a GetCapabilities request my aim was to generate a report listing the available map layers, and to check I had enetered all the required metadata. I had a look on the web to see if there were any stylesheets that would nicely format the data.
Mapfish JavaScript Toolbox
Mapfish is an open-source web mapping framework built using the Pylons Python web framework for “creating web services that allow querying and editing of geographic objects.” However the server-side functionality of the system I am currently working on is already handled by SQL Server 2008 Spatial and MapServer. What interested me more was that Mapfish “provides a complete RIA-oriented (Rich Internet Application) JavaScript toolbox.”
A couple of examples of the front-end interface can be found at the EU Inspire Geoportal, and the Marbled Murrelet Mashup. The Mapfish client combines three frameworks into one OpenLayers, GeoExt, and ExtJS.
The client JavaScript is available via downloaded from http://www.mapfish.org/downloads/. At the time of writing mapfish-client-1.2.tar.gz was the most recent version. The files can be unzipped using the open-source program 7-zip that handles both gzip and “tar ball” zip files. Once unzipped there are a number of samples that can be run and edited locally (look for the examples/map/index.html page). This alone is a huge step forward in creating a basic online mapping system that rivals proprietary offerings.
Further details on using the toolkit can be found at the Mapfish tutorial and this blog tutorial. I’ll also be writing some more technical posts, specifically around using Mapfish with Windows, as most of the current documentation assumes people are running Linux.
Quantum GIS and MapServer
One of the main barriers I had to using MapServer as a web GIS server was that layers had to be symbolised i
n a text editor, using a MAPFILE. It was cumbersome to keep editing and refreshing a browser, there was no easy way to check for errors, and you have to learn the syntax and keywords.
Whilst this is ok for smaller projects where I could make these myself, larger projects require non-programmers to gather data, symbolise it, and handle the map layouts and creation.
I’ve just discovered that another of the OSGeo‘s projects, Quantum GIS (often abbreviated to QGIS) has a tool that can take a map project created and symbolised in the desktop application, and export it to a MAPFILE which can be read by MapServer. This seems to be the missing link in a complete Open Source GIS stack.