Category Archives: GRASS GIS

Access GRASS 7 data in QGIS

QGIS supports GRASS in two different ways. 1) For those working with GRASS databases, there is the GRASS toolbox, which basically offered an alternative GUI to GRASS. For those working with other data types, most GRASS functions are now available through the processing toolbox.

I do most of my spatial analysis in GRASS, while I use QGIS amongst others to create maps based on the results. So I mostly used the GRASS toolbox. Unfortunately, the GRASS toolbox doesn’t work (yet) in QGIS 2.6. So what now? Well, as it turns out, QGIS can access GRASS raster layers through the QGIS browser. Continue reading

GRASS GIS 7.0.0 beta 3 is out, bringing further fixes and improvements

GRASS 7 sports very significant improvements and numerous new functions. For example, the improved graphical user interface makes it much easier to carry out complex GIS operations and handling of vector data has become much faster and more efficient with very large files. There is a large number of new analytical raster and vector modules and existing modules are now much faster (some even 1000 x faster). Beta 3 ships 390 fixes and improvements with respect to beta 2. For more details, go to http://grass.osgeo.org/news/37/15/GRASS-GIS-7-0-0-beta3/.

Exporting your GRASS raster using r.out.gdal? Check the createopt options!

GRASS GIS can export your raster layer in most common (and quite a few less common) data formats using theĀ r.out.gdal function (menu: file – export raster map – common raster formats). Exporting is so simple that you may forget that depending on the output format there are different options to optimise your output raster layer. Continue reading

Stable GRASS GIS 6.4.4 released

A new stable version GRASS GIS 6.4.4 has been released. It sports various bug fixes and a number of new features. Go here for more information.

You may be aware that there is also a GRASS GIS version 7. So which version should you go for? Well, it depends. Is long-term support, backward-compatibility with the GRASS 6 line and stability important to you. Or do you use the QGIS GRASS GIS toolbox a lot (which is not yet compatible with GRASS 7)? Go for the new GRASS 6.4 series.

Are you always looking for the latest of the latests, or is speed or the ability to handle very large data sets important to you? Have a look at list of new and improved features in GRASS 7. It is still in beta, so in theory less stable. But I should add that I am using this version for some time now (on Linux) and in my experience it is very stable.

Of course, you can also install both, they should run happily next to each other.

 

Creating a raster layer with a weighted random sample of points (or, my first attempt to create a python script)

I needed to create a raster map layer with a weighted random sample of all raster cells, using the percentage of crop land as weight. I couldn’t find a function to create such a weighted sample, so I decided to create a script to do this for me. Continue reading

One of those handy GRASS GIS functions I didn’t know about

Recently I needed to create a series of temporally interpolated rasters in between two input raster maps, viz., a suitability distribution map under climate conditions in 2000 and under projected climate conditions in 2020. I though this would be a good time to try out the new temporal database in GRASS GIS and use the t.rast.gapfill function, which replaces gaps in a space time raster data-set with interpolated raster maps using linear interpolation. Continue reading