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Opening MODIS tiles in QGIS
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:...
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Reading GRASS GIS vector attribute tables into R
Linking GRASS GIS and R will give you a very powerful set of geo-spatial analytical tools. The spgrass6 offers a very convenient interface between GRASS GIS and R. You can read more about this package...
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Converting an ArcMap layer file into an SLD document
Most open source GIS programs can open all most common, and quite a few obscure data format (thanks to the gdal library). What they can’t open is the ArcMap layer files (.lyr). A layer file defines...
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New GRASS GIS Web Site
The GRASS GIS web team has created a whole new website. The goal was to create a simplified structure, general update and nicer experience. And they certainly succeeded, it looks great! And navigating...
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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...
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Extracting lines ending with specific character using sed or grep
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...
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Spatialite 4.0 is out
The release of Spatialite 4.0 was just announced on the Spatialite user group. You can download it from the Spatialite website. And while you are on the website, check out the page about switching to...
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Stratified random sampling in GRASS GIS
There are various options to create a vector or raster layers with random sample points, including v.random, r.random and r.random.cells. The first two generate random points within the defined region....
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Stratified random sampling in QGIS
In my previous post I described how you can create a random stratified sampling using GRASS GIS. Unlike in GRASS GIS however, QGIS has a dedicated tool to do this. You can find it under ‘research...
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Import MODIS data in GRASS using r.in.gdal
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...
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Check out the new Landcover Polygon overlay function in the LecoS QGIS plugin
The author of the QGIS plugin LecoS came up with a new feature which might come in handy for some of you: a polygon overlay tool. This tool can extract raster values and save them directly to the...
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Improved r.mask in GRASS GIS 7.0
I am mostly using GRASS GIS 7.0, which is the development version. Main reason I started to use this version was the better (faster) vector handling. But there are many other new features and...
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Calculating the raster cell area of an unprojected raster layer
What if you get a raster layer with number of people per raster cell, like for example the population layer from Afripop, and you want to convert it to a population density layer? Well, obviously, you...
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New release candidate for GRASS 6.4.3 is out
The second release candidate of stable release 6.4.3 is available now. It contains a good number of improvements and especially stability fixes, see here for more details.Filed under: GRASS GIS,...
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Looking for a pdf reader with good annotations options
I read my articles on my (Android) tablet or on my computer (Ubuntu 12.10). On both, I want to be able to add notes and underline and highlight text. For Android there are various apps that allow you...
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Find Latitude and Longitude Values in Google Maps
Getting the coordinates of a location on Google maps isn’t as straight forwards as one may expect. But, as usual, if you know how, it is easy enough. And, there are actually several ways. What’s here?...
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Sum up values of neighbouring polygons – a GRASS GIS approach
How to sum up values of neighbouring polygons in QGIS? This question was asked on gis.stackexchange, with two interesting answers. One answer explains how to use Spatialite and SQL to achieve this. The...
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A quick look at the new GRASS Map Swipe Tool
I have just been trying out the new GRASS Map Swipe tool For now it is available in GRASS 7.0 but I understand it will be backported to GRASS 6 after some testing. The tool allows GRASS users to...
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Point coordinates to polygon – part I
Articles about field studies sometimes (but not always unfortunately) contain coordinates delimiting the boundaries of the field study. What if you want to view those boundaries in e.g., Google Earth?...
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Point coordinates to polygon – part II
In my previous article, I showed how you can convert point coordinates into a polygon vector layer in QGIS. So how about GRASS GIS? Like in my previous post, let’s assume you have a text file with two...
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