Monthly Archives: April 2012

Creating polar diagrams with confidence intervals in R

The function r.polar in GRASS GIS allows you to create simple polar diagrams of e.g., the slope aspect or wind directions. These polar diagrams make it easy to spot directional bias, for example in the distribution of the slope aspect within vegetation Fb in Figure 1. The next step is to test whether the observed bias is significant. Continue reading

two-minutes video tutorials for R

I just came across this blog with (by the time of writing) sixty two-minutes video tutorials on how to do things in R. Especially nice for those who like to learn by watching and listening. But do pay attention while watching because one way the videos are kept short isĀ  really fast talking…

Here is the link: http://www.twotorials.com/2012/04/sixty-two-minute-r-twotorials-now.html

If you run out of memory, split up your data

Most functions of GRASS can handle very large data sets. With a few functions you might run out of RAM though. One of these is the r.random.cell. This is a function that generates a random sets of cells with spatial dependence, i.e., that are at least a user-defined distance apart.

When this process takes up too much RAM, the solution is to divide the raster layer in a set of tiles Continue reading

ReshapeGUI – a tool to learn to use reshape2

The package Reshape2 in R is a very powerful tool to flexibly restructure and aggregate data. For users familiar with the pivot table function in Excel or Libreoffice/Openoffice, this tool offers similar (and more) functionality, albeit from the command line.

It’s flexibility comes with a price, it may not be extremely intuitive for the beginner. Continue reading