Thursday, 28 August 2014

Analysis of Crater Greg using LandSerf

I had some trouble with geomorphons, because I couldn't get the GRASS 7 extension to compile in Linux for unclear reasons, so I was limited to using the Windows version inside a virtual machine, and it decided to crash when presented with Mars data, although it was OK with Earth DTMs...

I have however been using LandSerf to generate curvature layers, and a feature classification, so here we are, for the well known (at least to Martian glaciologists) crater "Greg":

I hope you're not too confused by the use of transparency...

Units are in metres.

Some of the glaciers form a channel as they are constrained by topography, but not all channels are glaciers.....

Using longitudinal curvature calculated in LandSerf, showing negative curvature where a slope starts off steep and shallows as it goes down, which the Martian glaciers in Greg and elsewhere generally do, (Bryn Hubbard et al.):

Using RSGISLib to segment a layerstack consisting of nadir image, elevation, slope, aspect, and curvature layers:

Selecting all slopes above 15 degrees

Sunday, 24 August 2014

Geomorphons of mid-Wales

Following the machine-vision based method of topographic analysis, "Geomorphons" by Stepinski and Jasiewicz, here's an example of the method applied to mid-Wales:

The authors argue that the method can make a useful analysis of topography at differing scales, in a better way than typical differential-geometry based methods do.

A close-up of the Aberystwyth area:

The method is available either as an extension to version 7 of the open-source GRASS GIS software, or, for small datasets, as an online interface.

After a number of hours, a wider search area can be made to match the scale of Stepinski and Jasiewicz's map of Poland in their paper , in which the authors used a DEM at 30m resolution at a search radius of 50 cells.

Hopefully I'll have something useful from this method applied to Mars in time to go in my dissertation....

Website: Space Informatics Lab - University of Cincinnati

Thursday, 7 August 2014

Segmenting with LandSerf: Wales DEM

Using some more SRTM tiles, I will try segmenting the DEM of Wales, using the elevation, slope, aspect, and several curvature layers generated in LandSerf:

 Here is an example segmentation showing the mid-Wales area with RSGISlib with a minimum object size of 80 pixels (0.2sqkm):

Sunday, 3 August 2014

Segmenting Topography with LandSerf and RSGISLib

As a training for segmenting Martian topography, I have done a little work on Earth.

Using the software LandSerf  by Prof. Jo Wood (the website appears to be down at the moment), I created a number of derived topograhic layers from Shuttle Radar Topography mission data, i.e. slope, aspect, and plan, longitudinal,  cross-sectional, profile and mean curvature. I then layerstacked these files (taking the aspect in degrees from north-facing).

Using RSGISlib to segment these (using min 128px sized objects where a pixel is ~ 72m) I get results like this:

The curvature layers seem to enable it to segment along ridge and valley lines and it can sometimes be seen how the topography is orientated spatially.