[GRASS-user] curve sketching

[Hamish]

Martin Wegmann wrote:
> Hello, 
> 
> I am looking for a function related to "curve sketching"
> (Kurvendiskussion in  german) - I think r.series would be the perfect
> place for it, but before  submitting a wish, I just wanted to ask if
> there already exists a module  which fullfills this task.
> 
> If would be very handy to have functions like:
> 
> - point of global maximum (already in r.series -> max_raster)
> - point of global minimum (already in r.series -> min_raster)
> - turning point  (Wendepunkt)
> - point of max./min. slope (e.g. growing season, senescence)
> - information about unimodal/bimodal etc. phenology (no idea how to
> add this)
> 
> Some functions are listed on the german Wikipedia (1) - the eng.
> pendant is  not as elaborated (2)
..
> (1) http://de.wikipedia.org/wiki/Kurvendiskussion
> (2) http://en.wikipedia.org/wiki/Curve_sketching


Here's a way:

eval `r.univar -g elevation.dem | grep ^max=`
r.mapcalc maxelev="if(elevation.dem == $max, elevation.dem, null())"
r.out.xyz maxelev    # in GRASS 6.2 use "r.stats -1gn"

(may get multiple points with the same elev)

see also r.param.scale param=feature  (and other param opts)
and r.slope.aspect


I have wondered how to impelement topographic prominence for a DEM:
  http://en.wikipedia.org/wiki/Topographic_prominence
  http://en.wikipedia.org/wiki/List_of_mountains_by_prominence



Hamish