Monday, 5 January 2015

Geomorphons - processing British Isles SRTM DEM with GRASS7 r.geomorphon extension

Some time ago I mentioned Geomorphons, a machine vision based approach to topographic analysis promoted by Stepinski and Jasiewicz.

If you don't know what a geomorphon is, here's a link to the Space Informatics Lab at University of Cinncinati, see also the papers: Stepinski+Jasiewicz 2011, Jasiewicz + Stepinski 2013 

At the time I first came across this I had some trouble getting GRASS7 to install and get the extension working in Linux so I tried running GRASS7 in windows inside a VM but it didn't really work well.

Now however I have a working GRASS7 installation on Linux and here's a few demonstration maps, which show the broad categories of landscape position. Geomorphons use a line of sight approach best explained by the links and papers above.

I have used a search distance of L = 1000m in these maps, using Shuttle Radar Topography Mission data for the British Isles. I've set a threshold for flatness as 0.2 degrees, which is probably too small because in flat areas I'm not confident of the reality of these interpretations.

Geomorphons have a different kind of scale-dependence than the usual differential geometry based approaches used, though it is not independent of scale, it is more so than a simple slope analysis.

Co-ordinates are OSGB all-numeric throughout.

West Cornwall

SE Cornwall

N Cornwall

Aberystwyth area in mid-Wales
Mid-wales the same as above but with flatness threshold of 1 degree
Changing the threshold for flatness to 1.0 degrees, flat areas such as Borth Bog are shown as such on the map.

A closeup with 5m data:

Nevertheless I keep search distance L=1000m.

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