Author Archives: pvanb

About pvanb

I am a tropical forest ecologist with a focus on spatial and temporal patterns and processes at population and ecosystem level. I am furthermore very interested in issues related to conservation and sustainable use of biodiversity and natural resources under current and future climates. I have worked in the Middle East (Syria and Lebanon) and South America (Brazil) and in Eastern Africa (Kenya).

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 the 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

Sampling raster values at point locations in QGIS – an update

In a by now fairly old post I described how to sample raster values at point location in QGIS. The method I described used the ‘Point Sampling Tool’ addon. However, the function creates a new point layer, which only contains the values extracted from the raster layer. None of the fields in the original point layer is copied to the new one. It is possible to join the attribute table of the new vector point layer with the original attribute table afterwards using a spatial join as explained in that post. However, this will not work if your point data includes points with exactly the same coordinates.

Since I wrote that post, QGIS has come a long way. 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.

 

Using GDAL from within QGIS: trouble shooting

Some notes to self about steps I had to take to make GDAL work from within QGIS. Both where compiled from source and run without problems. However, there are still a few issues with running gdal from the QGIS processing toolbox. This may have to do with the fact that I installed both in a non-default location (in the /usr/local/ folder), but in any case, the steps below solved the problem for me. Continue reading

Installing Google Earth on Ubuntu 14.04

Since Ubuntu 13.10 Google earth cannot be installed out of the box on Ubuntu 64-bit systems because it  requires the deprecated ia32-libs package. The previous solution I wrote about, for Ubuntu 13.10, did not work this time. I got Google Earth to run, but it crashed all the time.

I then found the googleearth-package which downloads the latest stable Google Earth installer from Google and creates a package for you. You can then install and remove the created package at will.

But the easiest solution, Continue reading

A new search engine to search the R documentation

Just to quickly share this great new website where you can search the documentation of all R packages and functions available on CRAN (6688 R packages and 136342 R functions at the moment of writing!). It offers instant or advanced search options in an easy interface, and there is even a package that allows you to use the search functionality from within R. Check it out on http://www.rdocumentation.org/.

A Zim-wiki export template for a adaptive website

I wrote before about Zim, a graphical text editor used to maintain a collection of wiki pages. Although mostly aimed at individual use, notebooks can also be shared as html files (and a few other formats) by exporting the notebook or individual pages as web pages, as explained here. And to give you an idea what you can get, see here an example of one of my notebooks.

For one of my projects I wanted to create a small web-site with fact sheets that provide a short description of vegetation types in eastern Africa. These fact sheets go together with vegetation maps we have created for various countries in the region. The idea was to keep the fact sheets as notes in a Zim notebook, and use the export function to create a small web-site. Continue reading

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