Visualizing Terrain Surface Indicies with Scaled Arrows

Submitted by dylan on Sat, 2011-04-30 22:30.

Hamish Bowman recently posted a new GRASS module (d.barb) that can be used to depict the direction and magnitude components of some vector (e.g. wind) field along a raster surface or at points in space. An example (c/o Hamish):

The example above reminded me of an idea I once had, related to the depiction of potential
water/sediment fluxes along landscape gradients. In this case, the direction of the arrows would be determined by the dominant down-slope direction (aspect angle), and the magnitude of the arrows would be determined by some estimate of down-slope accumulation (CTI). It might look something like this:

Terrain shape indices depicted by scaled arrows: color describes mean curvature (red = convex, blue = concave), contours describe elevation surface, arrow direction is aspect angle, arrow magnitude is the comound topograpic index (CTI)Terrain shape indices depicted by scaled arrows: color describes mean curvature (red = convex, blue = concave), contours describe elevation surface, arrow direction is aspect angle, arrow magnitude is the comound topograpic index (CTI)

Curvature map

Dylan, can you tell me how do you get that curvature map? I already have a curvature map made from SAGA and SRTM data in a pixel basic, but i was trying to generate a more general one, like the one you have.

Regards!

Mean Curvature

Hi Guillermo,

Typically I generate slope and curvature maps using r.param.scale from GRASS GIS. This approach is nice in that it allows one to specify a window over which the terrain is generalized. See the manual pages for r.param.scale for ideas and citations. For the image used in this posting, the curvature was computed as part of an RST-interpolation of point data. I am not sure why, but curvatures computed as part of the RST interpolation are generally more generalized than what is typically generated via pixel-wise calculation.