[GRASS-user] Peak point extraction from DEM

[Amagine]

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