[GRASS-user] Peak point extraction from DEM

[Maciej Sieczka]

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