Sextante is quickly becoming the goto geoprocessing toolbox for me. I’ve been working with Sextante 1.0.8 on QGIS 1.8 and lately I’ve started looking into Sextante 1.1 for QGIS 2. This post highlights some of the main differences between the two versions. I’m sure there are many more hidden gems I have not discovered so far.

One thing you will notice if you have used previous versions of Sextante is that the new version comes with a simplified interface which groups tools into three categories: geoalgorithms, models, and scripts. If you prefer the old style grouping by algorithm source such as GDAL, GRASS, etc. you can switch to the Advanced interface.

advanced

simplified

Let’s start with the bad news: Models created in 1.0.8 are not compatible with 1.1 since many of the algorithms have been rearranged in new categories and Sextante cannot find them by their old names anymore, e.g.

1.0.8 … ALGORITHM:ftools:fixeddistancebuffer
1.1 … ALGORITHM:qgis:fixeddistancebuffer

The great news is that the modeler has been improved greatly. Model representations now show the flow of input and output data through the model steps much more clearly:

Sextante 1.0.8 modeler

Sextante 1.1 modeler

I also found the new modeler much more stable – no crashes so far. *fingerscrossed*

Another nice new feature is Sextante commander which can be started using the shortcut Ctrl+Alt+M. It’s a quick launch solution for all Sextante algorithms:

At FOSS4G, I’ll be presenting some work I did evaluation OSM using Sextante 1.0.8. I’d love to hear how you are using Sextante.

This post covers how to add you own tools to expand Sextante’s ftools toolbox.

I was looking through Sextante for a tool that inserts additional nodes into a linestring at intervals of my choice. I couldn’t find that exact tool but I found something similar: Densify Geometries in ftools which adds the same number of nodes to all line segments. So I decided to modify Densify Geometries to fit my requirements.

Ftools scripts (such as DensifyGeometries.py) are located in ~/.qgis/python/plugins/sextante/ftools. To create my modified version, I just copied the original and modified the code to accept a densification interval instead of a number of nodes. Since I didn’t know how to add my new tool to Sextante I contacted the developer mailing list and after a short coffee break I had the answer (thanks Alexander!):

The new algorithm has to be exposed in the provider FToolsAlgorithmProvider.py. To do that: Add an import statement for the new algorithm (using existing statements as examples) and add the algorithm to the list self.alglist in the __init__() method. That’s it!

Sextante automatically creates the input form you can see in above screenshot. Very handy! And the new tool can be added to geoprocessing models just like any of the original ones.