[GRASS-user] 回覆： Re: ridge extraction from DEM

[Markus Metz]

On Tue, Jun 12, 2012 at 11:28 AM, Margherita Di Leo <diregola at gmail.com> wrote:
> Hi,
>
> there is also r.convergence add-on:
> http://grass.osgeo.org/wiki/GRASS_AddOns#r.convergence

BTW, the topographic convergence index is also available in
r.watershed in GRASS 7.

Markus M

>
> Regards,
> madi
>
> On Tue, Jun 12, 2012 at 4:24 AM, Michael Barton <michael.barton at asu.edu>
> wrote:
>>
>> Invert the DEM by multiplying all values by -1 and adding the maximum
>> original height value. This makes the maximum height 0 and everything less
>> than that increasingly greater than 0
>>
>> Run r.watershed on the inverted DEM choosing stream segments as output.
>>
>> The stream segments from the inverted DEM are your ridgelines. You can
>> keep them in raster or thin them (r.thin) and convert them to vector
>> (r.to.vect).
>>
>> I've copied the GRASS user list again because this is a general question
>> that others might be interested in.
>>
>> Michael
>>
>>
>>
>> On Jun 11, 2012, at 7:29 PM, Thomaswplee wrote:
>>
>> How to make ridge vector line with reversed accumlated flow as in
>> watershed?
>>
>> Still reverse DEM plus vectorization of ridge raster?
>>
>> Thomas
>>
>>
>>
>> -------- Original message --------
>> Subject: Re: ridge extraction from DEM
>> From: Michael Barton <michael.barton at asu.edu>
>> To: thomaslee at starvision.com.hk
>> CC: grass-user grass-user <grass-user at lists.osgeo.org>
>>
>>
>> Thomas,
>>
>> I don't remember posting anything about r.ppa. I did a quick search and
>> found a post by Māris Nartišs
>> (http://lists.osgeo.org/pipermail/grass-user/2005-October/030883.html).
>>
>> r.param.scale will extract ridges. You will need to adjust the optional
>> parameters (especially processing window size) to get the ridges you want.
>>
>> An alternative method is to invert the DEM and run r.watershed on it,
>> extracting the 'streams'. The 'streams' of the inverted DEM will follow
>> ridges.
>>
>> Michael
>>
>>
>>
>> On Jun 11, 2012, at 9:26 AM, <thomaslee at starvision.com.hk>
>> wrote:
>>
>> > Dear Michael,
>> >
>> > I am interested in ridge extraction but not able to find the r.ppa
>> > mentioned by
>> >
>> >
>> > Chang, Y.C., Frigeri, A., 2002. Implementing the automatic
>> > extraction of ridge and valley axes using the PPA algorithm in
>> > Grass GIS. In: Open Source Free Software GIS GRASS
>> > Users Conference, 2002.
>> >
>> >
>> > Implementing the automatic extraction of ridge and
>> > valley axes using the PPA algorithm in Grass GIS
>> >
>> >
>> > Do you have any solution since your message in 2007 about ridge
>> > extraction.
>>
>> _____________________
>> C. Michael Barton
>> Visiting Scientist, Integrated Science Program
>> National Center for Atmospheric Research &
>> University Corporation for Atmospheric Research
>> 303-497-2889 (voice)
>>
>> Director, Center for Social Dynamics & Complexity
>> Professor of Anthropology, School of Human Evolution & Social Change
>> Arizona State University
>> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>>
>>
>> _____________________
>> C. Michael Barton
>> Visiting Scientist, Integrated Science Program
>> National Center for Atmospheric Research &
>> University Consortium for Atmospheric Research
>> 303-497-2889 (voice)
>>
>> Director, Center for Social Dynamics & Complexity
>> Professor of Anthropology, School of Human Evolution & Social Change
>> Arizona State University
>> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>>
>>
>>
>>
>>
>>
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>>
>
>
>
> --
> Dr. Margherita Di Leo
>
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