Wow, thanks Maciek!
r.mapcalc sounds like a great tool for my needs!
Yah, looks like you understand my intent.
thanks again! I never get such thorough and clear answers on the
ArcGIS side.
Kudos to the GRASS community.
Mars
On 2-Jul-07, at 1:21 AM, Maciej Sieczka wrote:
Amagine wrote:
Thanks Martin, I'll have a look at terrain analysis in grass. See
what I can come up with.
I would like to be able to regulate the following parameters:
Minimum height of peak
A topographic "peak" will have an elevation, not a range of
elevations. So I'm not sure what you mean.
I should have elaborated further.
Minimum height of peak, meaning do not classify any peaks below a
set minimum threshold : 1000 m for instance.
You can use r.mapcalc for that, after r.param.scale, like:
r.mapcalc 'peaks_1km=if(dem>=1000,peaks,null())'
Minimum drop of surrounding peaks
Not sure what you mean here too.
Meaning a peak is not extracted if there are surrounding elevations
within a minimum drop amount eg. 50m or 100m (depending on accuracy
of DEM file and refinement desired of distinct peaks)
Maybe you could use slope, calculated from dem, to filter these out
with r.mapcalc?
summit points optional hierarchy...
I guess these are technical mountaineering terms? So again I'm not
sure what data you are hoping to extract.
Summit points.... The highest point on a peak.
pseudo-pseudo code:
r.cluster: create a raster map where each peak has a unique value
r.info -r: find out the number of peaks
for each summit do :
r.mask: set a mask to match one of the peak spots created by
r.cluster
r.mapcalc: extract the peak falling into this spot
r.info -r: find out it's max value
r.mapcalc: extract the reported max (summit) into another raster
done
r.patch: patch all summits, if needed
So a peak encompasses all vertical surface areas within the "Summit"
point based on the above two categories.
I suppose I define a peak as a categorical area, and a summit as a
point. Perhaps there are better definitions.
Hierarchy in my mind would be to classify peaks within peaks. Based
on the initial two parameters (Minimum height of peak, minimum drop
of surrounding peaks)
I suppose I should draw a picture :) probably make more sense.
I hope I got you right.
Best
Maciek
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