PyGRASS equivalent of piping results from one function to another

When using GRASS commands on the command line, one very neat little trick is to ‘pipe’ results from one function directly to another. An example I used in an earlier post is:

r.category My_map | r.category My_map rules=-

So, how does that works in python using pygrass?
Continue reading “PyGRASS equivalent of piping results from one function to another”

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

Multivariate Environmental Similarity Surfaces (MESS) index in GRASS GIS

The Multivariate Environmental Similarity Surfaces (MESS) is an index that represents how similar a point in space is to a reference set of points, with respect to a set of predictor variables (Elith et al 2010). The function was first implemented as part of the Maxent software package, and is also available in the dismo package for R (see also here and here).

The latter works well on small and medium sized data sets. However, they take a long time to run on larger data sets, e.g., when working with 1km² raster grids covering eastern Africa. I therefore wrote a small R script to compute MESS in GRASS GIS. Continue reading “Multivariate Environmental Similarity Surfaces (MESS) index in GRASS GIS”

Start R inside GRASS but keep the terminal prompt

I often run R from within GRASS GIS. For example using R as a scripting language to automate GIS analysis. Or to use statistical models in R on spatial data in GRASS.

I used to open R in the terminal. However, I am using more and more RStudio instead. This has one drawback. When opening RStudio in the terminal (or any other program for that matter), you cannot use that command prompt anymore. Continue reading “Start R inside GRASS but keep the terminal prompt”

R/GRASS connection: more than the sum of its parts

GRASS GIS is a very powerfull GIS offering an extensive set of tools for geospatial data management and analysis, image processing, and spatial modeling. The possibility to directly interact with R further improves the geospatial analysis capabilities of GRASS (see R Spatial View). Continue reading “R/GRASS connection: more than the sum of its parts”

Finding and renaming long file names with R

I have never given it a though, but there is apparently a limit to the length of file names that can be handled by Windows Explorer of Windows XP. I found out when trying to copy my Zotero folder to a computer with Windows XP. I was getting error message of folders that could not be copied, suggesting that my HD was full. I checked a few of these folders and they all contained one or more files with very long file names (>250 characters). Continue reading “Finding and renaming long file names with R”