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
NASA offers access to its MODIS and ASTER data sets through Reverb|Echo. The data comes in HDF format and uses the Sinusoidal grid tiling system. If your gdal is compiled with HDF4 support (use ./configure –with-hdf4), you can use gdal, or any software that uses gdal, to open the downloaded MODIS tiles directly. For example in QGIS as explained here or in GRASS GIS.
A quick note (to myself mostly) about how to extract lines from a text file that end with a specific set of characters. In Linux, you can very easily do this using ‘grep’ or ‘sed’. But, first a little bit of background. Continue reading
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
NASA offers a very convenient web-based tool to select and download the tiles you need; Reverb / ECHO. The tiles are in HDF format and use the Sinusoidal grid tiling system (proj4 definition:
+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs). But you probably want to have the data in another data format and in another projection. NASA offers a very convenient cross-platform tool to reproject and convert the data (it also makes it very easy to mosaic tiles): the Modis Reprojection Tool (MRT).
Freeplane is a great mind mapping software. I use it e.g., to jot down and organize notes from articles I am reading, creating lists of software, relevant websites, etc.
One of the advantages of Freeplane is that you can export your mind map in many formats. This including different formats for online publishing, e.g., as java applet or a clickable map image version.The java applet offers a basic interface to your mindmap, including search and expanding / collapsing of the nodes. Continue reading
The development of open source spatial tools is amazing. A while ago I wrote how one could create mobile maps using a range of tools, including GRASS or QGIS, Maptiler, and Mobile Atlas Creator (MOBAC).
A short note on how to create a spatial table from a table with latitude and longitude coordinates in your SQLite / Spatialite database. In the example below, the table I am working with is ‘labels’. Continue reading
To create a Google earth map, I would normally export my raster layers as a geo-referenced png file and subsequently use maptiler (or gdal2tiles.py) to create the Google earth map (see here for more details). Because I want to create a map based on several layers, I can not simply export a raster layer. Instead, I need to create a map in QGIS map composer and georeference that map, following the steps described here.
Unfortunately, as it turns out there are limits in the size of the map you can create in QGIS map composer. Perhaps there is a way to increase this, but I am not sure how. An alternative solution is to smaller create sub-sets of the map. But how to get them together as one Google earth map again? Continue reading
In R to create a contingency table of the counts of the combination of two variables, I would normally resort to table(). But how fast is it? A question that becomes more relevant when working on large tables and when you have to run it very often. As you will see in the examples below, it isn’t terribly fast and there are other ways to create cross tables faster. Continue reading