In a recent post Anita Graser (aka underdark) showed how to create illuminated or Tanaka contours in QGIS using various functions available in the toolbox and some custom functions.
Here I want to explore a slightly different way to achieve the same, using GRASS GIS to compute the azimuth, brightness and line width. I’ll use the command line, but you can do the same using the menu in GRASS, or the corresponding GRASS functions in the QGIS processing toolbox.
In R you can use system calls or the spgrass6 package to run GRASS GIS functions. To do this, you need to run R from within GRASS GIS. This is as simple as starting GRASS GIS and subsequently starting R from the command line. See the GRASS-wiki for a more detailed background.
The issue at hand
One of the user-cases is when you want to (1) run a GRASS function on e.g., a raster layer and (2) capture the console output in a R data frame. For example, you can run the following in R:
MyVariables <- execGRASS("r.stats", flags="c", input="MyMap", separator=",", intern=TRUE)
However, the output is not in a very convenient format. Continue reading
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 is really fast talking…
Here is the link: http://www.twotorials.com/2012/04/sixty-two-minute-r-twotorials-now.html
There are so many functions in GRASS GIS that it is easy to miss one or two. One functions I recently came across through this tutorial is the d.polar function.
This function draws a polar diagram of angle map such as aspect or flow directions. Continue reading
Outdoor sport or field work, a GPS has become indispensable. But what if you want to use your own maps? If you are using an Android smartphone and one of the map viewers available on android market, this is fairly easy. You’ll need your favorite GIS application (e.g., GRASS or QGIS), Maptiler, and Mobile Atlas Creator (MOBAC). Continue reading
I just came across the Dutch QGIS site: www.qgis.nl. The objective of the website is “to create a platform for native speakers AND to discuss / explore typical dutch ideas or problems”.
But the tutorials on this site will not only be useful for the Dutch (speaking) community. All tutorials (that I have seen) are available in both Dutch and English. Check it out…
Geospatial analysis guide
I just found, through this blog, a very nice text book on geospatial analysis; Geospatial Analysis – A comprehensive guide by M. de Smith, P. Longley and M. Goodchild. The book covers a wide range of topics such as “Conceptual Frameworks for Spatial Analysis”, “Data Exploration and Spatial Statistics”, “Statistical Methods and Spatial Data”, “Exploratory Spatial Data Analysis”, “Grid-based Statistics”, “Spatial Autocorrelation”, and “Network and Location Analysis”. Also very nice, it includes an overview of some of the main spatial statistical packages for R. Continue reading