Terrain attribute selection in environmental studies

Exploring species-environment relationships is important for amongst others habitat mapping, biogeographical classification, conservation, and management. And it has become easier with (i) the advance of a wide range of tools, including many open source tools, and (ii) availability of more relevant data sources. For example, there are many tools with which it is relatively easy to create a wide range of derived terrain variables using digital elevation (DEM) or bathymetric (DBM) models. However, the ease of use of many of these tools, especially when used by non-experts, may lead to the selection of arbitrary or sub-optimal set of variables. In addition, derived variables will often be highly correlated (Lecours et al. 2017).

Continue reading “Terrain attribute selection in environmental studies”

The first release candidate of GRASS GIS 7.2.0 is out

I have been using the development version for some time now, and all I can say is that you definitely should give the new GRASS GIS 7.2.0RC1 release a try. It is, in my experience, very stable, and it provides more than 1900 stability fixes and manual improvements compared to the stable releases 7.0.x.

It also features a number of new modules. A favourite of mine is the new g.gui.datacatalog which makes it so much easier to browse, modify and manage GRASS maps across map sets and locations. Also very welcome is the new d.legend.vect module which can be used to display a vector legend in the active graphics frame. And for those that are into space-time analyses, there are also a number of new modules for the temporal framework.

For more information about all the improvements and changes, see the detailed announcement. And while you are at it, don’t forget to check out the add-ons, some great new ones have been added and updated in the last few months.

And last but not least, a big thanks to the developers!




Climate data sets, which one to select?

For species or vegetation modelling, one of the first choices to make is the selection of explanatory variables, which in most cases will include climatic or bioclimatic data sets. One of the most widely used global climate data sets in biogeographic and ecological research is from Worldclim (Hijmans et al., 2005). Alternative global rainfall data sets are from TAMSAT TARCAT (Maidment et al., 2014) and CHIRPS (Funk et al., 2014). The Worldclim data layers are based on an interpolation of average monthly climate data from weather stations. The other two data sets combine weather station data with satellite observations to improve accuracy where in situ rainfall measurements are sparse. All three data sets are available from the KITE resources website as part of the Africlim dataset (Platts et al. 2015). Continue reading “Climate data sets, which one to select?”

Use R to get gbif data into a GRASS database



The Global Biodiversity Information Facility (GBIF) is an international open data infrastructure that allows anyone, anywhere to access data about all types of life on Earth, shared across national boundaries via the Internet. GBIF provides a single point of access through http://www.gbif.org/ to species records shared freely by hundreds of institutions worldwide. The data accessible through GBIF relate to evidence about more than 1.6 million species, collected over three centuries of natural history exploration and including current observations from citizen scientists, researchers and automated monitoring programs.

There are various ways to import GBIF data, including directly from the website as comma delimited file (csv) and using the v.in.gbif addon for GRASS (I’ll post an example using this addon at a later stage). Here, however, I’ll use the rgbif package for R to obtain the data. In the link section some tutorials are listed that illustrate the use of other R packages. Continue reading “Use R to get gbif data into a GRASS database”

VIF stepwise variable selection


In modelling, multicollinearity in the set of predictor variables is a potential problem. One way to detect multicollinearity is the variance inflation factor analysis (VIF). In GRASS GIS, the VIF for a set of variables can be computed using the r.vif addon. This addon furthermore let’s you select a subset of variables using a stepwise variable selection procedure, in which variables are removed till the highest VIF values is less than a user-defined threshold value. In this post I introduce the addon and provide some examples how to use the addon. Continue reading “VIF stepwise variable selection”

Sample raster values at point location in QGIS – yet another way

A while back I wrote how one can sample raster values at point locations in QGIS using the Saga function ‘Add grid values to point’, which is available in the processing toolbox. Recently it was reported here that values uploaded from a floating raster layer are rounded up to an integer. I tried it myself in Saga, and it seems to work fine for me. But if you are running in problems with a function, it is good to remember that in QGIS you have have access to many libraries from multiple software tools. This means there are often more than one way to get things done.

And indeed, the processing toolbox offers another tool to sample raster values at point location; the GRASS GIS v.what.rast.points function. In this post I describe how to use this tool directly in GRASS, but you can use the tool in QGIS as well, as illustrated below. Continue reading “Sample raster values at point location in QGIS – yet another way”